Unveiling the Potential of Reduced Graphene Oxide in Self-Powered Photodetectors.

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Learn more: PMC Disclaimer | PMC Copyright Notice Chemphyschem . 2026 Apr 10;27(7):e202500382. doi: 10.1002/cphc.202500382 Search in PMC Search in PubMed View in NLM Catalog Add to search Unveiling the Potential of Reduced Graphene Oxide in Self‐Powered Photodetectors Bitap Raj Thakuria Bitap Raj Thakuria 1 Department of Chemistry, Gauhati University, Guwahati, Assam, India Find articles by Bitap Raj Thakuria 1 , Indranee Hazarika Indranee Hazarika 2 Morigaon Polytechnic, Morigaon, Assam, India Find articles by Indranee Hazarika 2 , Bedanta Gogoi Bedanta Gogoi 3 Department of Chemical Sciences, Tezpur University, Tezpur, Assam, India Find articles by Bedanta Gogoi 3, ✉ , Amreen Ara Hussain Amreen Ara Hussain 4 Institute for Plasma Research, Gandhinagar, Gujarat, India 5 Homi Bhabha National Institute, Mumbai, India Find articles by Amreen Ara Hussain 4, 5, ✉ Author information Article notes Copyright and License information 1 Department of Chemistry, Gauhati University, Guwahati, Assam, India 2 Morigaon Polytechnic, Morigaon, Assam, India 3 Department of Chemical Sciences, Tezpur University, Tezpur, Assam, India 4 Institute for Plasma Research, Gandhinagar, Gujarat, India 5 Homi Bhabha National Institute, Mumbai, India * Bedanta Gogoi: ( [email protected] ), Amreen Ara Hussain: ( [email protected] ) ✉ Corresponding author. Revised 2026 Jan 29; Received 2025 May 29; Accepted 2026 Feb 24; Issue date 2026 Apr 14. © 2026 The Author(s). ChemPhysChem published by Wiley‐VCH GmbH This is an open access article under the terms of the http://creativecommons.org/licenses/by-nc-nd/4.0/ License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. PMC Copyright notice PMCID: PMC13068507  PMID: 41963105 Abstract Self‐powered photodetectors have emerged as advanced devices, gathering significant attention in the field of optoelectronics, particularly for their potential in power‐scarce environments. These devices can detect light and generate an electrical current with minimal or no external power supply. However, designing self‐powered photodetectors presents challenges, particularly in material development, as not all materials can generate photocurrent without an external power source. The ability to convert light energy into electrical energy depends on the material's intrinsic properties. In this context, reduced graphene oxide (rGO) has proven to be a promising candidate due to its high electrical conductivity, tunability, photoconductive properties, scalability, environmental stability, and self‐powered capability. These properties can be further optimized through the controlled reduction of graphene oxide. Utilizing these attributes, rGO‐based self‐powered photodetectors can achieve high performance and practicality, making them suitable for various optoelectronic applications, from wearable electronics to environmental monitoring. This review revisits recent advancements in rGO‐based self‐powered photodetectors, focusing on their efficiency and device architecture. Additionally, a comprehensive overview of their synthesis methods is provided. The review also discusses prospects and the challenges associated with designing self‐powered photodetectors. Keywords: reduced graphene oxide (rGO), optoelectronics, photodetector, self‐powered 1. Introduction Photodetectors are vital components in the realm of optoelectronics, functioning as transducers that convert incident light (photons) into electrical signals, either in the form of current or voltage [ 1 ]. This photon‐to‐electron conversion is facilitated by several fundamental physical mechanisms, including the photoconductive effect , photovoltaic (PV) effect , photo‐thermoelectric effect, and bolometric effect [ 2 ]. These effects govern the behavior of photodetectors under illumination and determine the nature of the output electrical signal in response to varying light intensities and wavelengths. At the heart of a photodetector lies a semiconducting material, whose electronic structure enables it to absorb photons with energies equal to or greater than its bandgap. When the photodetector is illuminated, photons are absorbed by the semiconductor, leading to the excitation of electrons from the valence band to the conduction band. This process creates electron–hole pairs, also known as photo‐generated charge carriers. The generation rate of these carriers depends on several factors including the intensity and wavelength of the incident light, the absorption coefficient of the semiconductor, and the thickness of the active layer. Once generated, these charge carriers must be efficiently separated and transported to the electrodes for external collection, resulting in the generation of a photocurrent. In traditional photodetectors, an external bias voltage is applied across the device to establish an electric field that aids in the directional drift of these carriers, i.e., electrons toward the anode and holes toward the cathode. This externally driven separation mechanism ensures high efficiency in charge collection and is particularly useful in enhancing the speed and sensitivity of the device. However, the reliance on an external power source introduces significant limitations, especially for applications where power accessibility is constrained or where device miniaturization and autonomy are required. For instance, in portable electronics , wearable sensors , remote sensing systems, or space‐borne devices, it is often challenging to maintain a continuous external power supply. Furthermore, in hazardous or extreme environments, wiring for external biasing may not be feasible, and energy efficiency becomes a critical design criterion. Consequently, these constraints have driven a surge in research aimed at developing self‐powered photodetectors, devices capable of operating without external electrical power [ 3 ]. These next‐generation detectors utilize built‐in electric fields, typically present in specially engineered junctions, to autonomously separate and drive photo‐generated carriers, thereby enabling photocurrent generation under illumination alone. Based on their operating mechanisms and structural configurations, self‐powered photodetectors can be broadly classified into three categories: (i) p–n junction photodetectors , which utilize the built‐in electric field at the interface between p‐type and n‐type semiconductors to separate charge carriers [ 4 ]; (ii) Schottky junction photodetectors , which exploit the barrier potential formed at the metal–semiconductor interface for carrier separation [ 5 ]; and p hoto‐electrochemical ( PEC ) photodetectors , where photon absorption in a semiconductor immersed in an electrolyte leads to redox reactions that generate photocurrent [ 6 , 7 ]. The evolution toward self‐powered operation not only enhances the energy efficiency of photodetectors but also expands their applicability in a broad spectrum of real‐world scenarios where traditional power‐reliant devices fall short. The performance evaluation of photodetectors is crucial for determining their suitability for specific applications and is based on several key parameters. Among the most important of these is the photocurrent magnitude, which refers to the amount of current generated under illumination and provides a direct measure of the device's light sensitivity. Another essential parameter is photo‐responsivity (R), typically expressed in amperes per watt (AW −1 ), which quantifies the output electrical signal (current or voltage) per unit of incident optical power. It is represented as R λ = I ph / P opt , where I ph = I Light − I Dark refers to the photocurrent and P opt is the incident optical power on the effective illuminated area of the device. (If the illumination is reported as power density P, and S is the effective illuminated area of the device, then P opt = PS and the definition reduce to R ( λ ) = I ph /(PS).) Higher photoresponsivity indicates that the device can generate more electrical signal from a given amount of light, thereby enhancing sensitivity. Another critical metric is specific detectivity (D), usually expressed in Jones (cm Hz 1/2 W −1 ), which reflects the ability of a photodetector to detect weak optical signals amidst background noise. It is calculated using the relation D * = R λ /(√2 e × I Dark ). Another vital parameter to assess photodetectors is external quantum efficiency (EQE), representing the efficiency of converting photons into electrons. It is represented as EQE = ( h c/ eλ ) R λ × 100%. Here, h , c , λ are the Planck constant, the speed of light, and the applied wavelength λ , respectively [ 8 , 9 ]. It considers not only the responsivity but also the noise level and active area of the detector, thus serving as a comprehensive measure of performance under low‐light conditions. Response time, which includes both rise time and fall time, determines the speed at which the photodetector can react to changes in light intensity. Fast response times are essential for applications such as optical communication and imaging, where rapid detection and processing of optical signals are necessary. A distinguishing advantage of self‐powered photodetectors lies in their exceptionally low dark current, i.e., the residual current that flows through the device even in the absence of light. In conventional photodetectors, dark current can be a significant source of noise, reducing the signal‐to‐noise ratio and limiting the device's performance, particularly in low‐light scenarios. In contrast, self‐powered photodetectors, due to their intrinsic junction‐based operation and absence of external bias, often exhibit minimal leakage currents, enhancing both sensitivity and energy efficiency. In addition to low dark current, these devices are characterized by high photo‐responsivity, fast photo‐response and recovery times, and substantial light on/off ratios (the ratio of photocurrent under illumination to the current in the dark), which are indicative of sharp switching behavior and operational precision. These features collectively make self‐powered photodetectors highly attractive for a wide range of practical and emerging applications. In terms of application areas, self‐powered photodetectors are finding increasing adoption across diverse technological sectors. Their autonomous operation and minimal energy demands make them ideal candidates for remote sensing systems, especially in environments where continuous power sources are unavailable, such as in space exploration, environmental monitoring, and disaster management. They are also integral to security surveillance systems, where continuous, real‐time monitoring is required. In nondestructive testing, self‐powered detectors enable the assessment of materials or structures without causing damage, particularly useful in the aerospace, construction, and manufacturing industries. In optical communication networks, the fast response characteristics of these devices support high‐speed data transfer. Moreover, they are increasingly used in biomedical diagnostics, such as wearable health sensors and imaging systems, and in environmental applications such as air and water quality monitoring, where remote operation and minimal maintenance are crucial. From a materials engineering perspective, the selection of semiconducting materials plays a pivotal role in the overall performance and stability of photodetectors. Within the class of carbon‐based nanomaterials, reduced graphene oxide (rGO) has gained substantial attention as a versatile and tunable functional material. Compared to graphene oxide (GO), rGO contains fewer oxygen‐containing functional groups, which translates into enhanced electrical conductivity, better thermal stability, and greater environmental resistance. These properties enable rGO to effectively serve as a conductive channel or active material in photodetector architectures. Furthermore, rGO can form heterojunctions with a wide range of semiconducting materials, such as metal oxides (MOs) (e.g., ZnO, TiO 2 ), transition metal dichalcogenides (TMDCs) (e.g., MoS 2 , MoSe 2 ), and perovskite materials, giving rise to hybrid nanocomposites that combine the advantages of multiple material systems. Such rGO‐based composites enhance several aspects of photodetector performance, including broadband light absorption, efficient photocarrier generation, rapid carrier transport, and low recombination rates. These synergies are particularly beneficial in self‐powered configurations, where optimizing internal electric fields and charge separation mechanisms is critical. As a result, rGO and its hybrid systems are increasingly being explored in next‐generation optoelectronic devices, including photodetectors, solar cells, and flexible electronic components. The discovery and subsequent research on graphene have revolutionized the field of materials science and nanotechnology. In 2010, Professors Andre Geim and Konstantin Novoselov were awarded the Nobel Prize in Physics for their pioneering work on the isolation and characterization of monolayer graphene—a two‐dimensional (2D) allotrope of carbon with exceptional mechanical, electronic, and thermal properties [ 10 ].This recognition not only validated the significance of their discovery but also triggered a massive global wave of research focused on developing graphene derivatives with tunable properties to suit a wide array of technological applications. Among these derivatives, GO and rGO have emerged as particularly attractive materials due to their ease of synthesis, functional versatility, and compatibility with other nanomaterials. While GO is rich in oxygen‐containing functional groups and offers good dispersibility in aqueous media, rGO exhibits superior electrical conductivity, thermal stability, and chemical inertness due to the partial restoration of the π‐conjugated sp 2 carbon network. These characteristics make rGO highly desirable for integration into various device architectures. Over the past decade, GO and rGO have been successfully employed in a multitude of applications, including photonics, nanoelectronics, energy storage and harvesting, electrocatalysis, biomedicine, and sensing. Their appeal lies in their combination of high electron mobility, large specific surface area, optical transparency, and exceptional mechanical strength, all of which are critical for developing high‐performance functional materials and devices [ 11 ]. rGO has several advantages over GO due to its high C/O ratio, which enhances its electrical and thermal conductivity. Additionally, rGO possesses a greater specific surface area and higher mechanical strength, which makes it suitable for diverse applications as depicted in Scheme 1 . SCHEME 1. Open in a new tab Various applications of rGO. Because the electronic/defect landscape of rGO depends strongly on the reduction route, differences in synthesis often translate into different work function, conductivity, and interfacial band alignment ultimately changing zero‐bias charge separation and photodetector figures of merit. For clarity, we summarize common GO→rGO reduction routes and their reported property–performance links in Table 1 . TABLE 1. Linking rGO reduction routes to electronic properties, interfacial band alignment, and photodetector performance metrics. Sl. no. Material/system rGO preparation/reduction Electronic/materials properties (rGO) Device physics link Metrics References 1 SnSe 2 ‐rGO/MoS 2 /Si (bulk heterojunction) Solvothermal GO→rGO (EG, 180°C, 24 h) WF (lit.) ~4.7 eV; conductive pathway (qual.) Built‐in field; bulk heterojunction R : 13.75 A/W @900 nm [ 12 ] D *: 5.08 × 10 12 Jones t r / t f : ~110/110 ms 2 LSG/CsPbBr 3 Laser GO→LSG (450 nm; ~200 mW opt.) Conductive pathway; contact R < 0.25 kΩ PTE dominated Range: 405 nm–118 µm [ 13 ] R : ~100 mA/W @405 nm ( R max 135 mA/W) D *: 1.6 × 10 11 Jones t r / t f : 32/18 ms NEP min : ~10 pW Hz −1/2 3 WS 2 /rGO Hydrothermal in situ (200°C, 12 h) Conductive pathway (qual.) PEC interface field R : 9.3→5.7 µA/W [ 14 ] I on / I off : ~1.23 J(0 V): ~0.67 µA cm −2 J photo : 0.24→4.32 µA cm −2 (0→0.8 V) Stability: 100 cycles 4 Se microtube/rGO (p–p) Thermal (150°C, 260 min, N 2 ) WF ~ 4.12 eV; O/C ratio decreases; E g 2.29→1.02 eV Type‐II p–p, depletion R : 168.1 mA/W @368 nm [ 15 ] D *: 1.48 × 10 11 Jones t r / t f : 18 µs/4.76 ms on/off: 1049 V oc : ~0.2 V I dark : ~3 pA NEP: ~4.1 × 10 −14 W Hz −1 ′ 2 5 ZrO 2 ‐rGO NFs/n‐Si Electrospinning (rGO powder); calcine 500°C, 1 h p‐type role (qual.) p–n depletion field R : 3 mA/W (Vis, −2 V); 0.63 A/W (365 nm, −2 V) [ 16 ] D *: 2.33 × 10 10 (Vis); 1.04 × 10 10 (365 nm) RR: 3.7384 × 10 4 (±2 V, dark) on/off: 6135 (Vis, −2 V); 5.5 × 10 3 (365 nm, −2 V) V oc : up to 0.42 V I sc : up to 278 µA (150 mW cm −2 ) I s (dark): 1.8 × 10 −10 A at −2 V 6 Ag/rGO‐SnO 2 NRs GO (Hummers)→rGO during Ag anchoring Raman I D / I G 1.08 (Ag/rGO) PEC + Ag‐LSPR + transport Range: 365 nm [ 17 ] t r / t f : 0.341/0.068 s (Ag/rGO‐SnO 2 ); 0.072/0.05 s (TiCl 4 ‐treated) on/off: 195 (vs 66); 1441 (TiCl 4 ) J sc : 0.29 vs 0.14 mA cm −2 (0 V); 5.4 mA cm −2 (TiCl 4 ) 7 rGO/n‐Si Hydrazine reduction (90°C), drop‐cast Raman D/G ~ 1.4; WF (lit.) 4.66 eV Built‐in field (qual.) Range: 365–1200 nm [ 18 ] R : 1.52 A/W @600 nm t r / t f : 2/3.7 ms on/off: >10 4 I dark : ~1 nA V bi : ~0.4 eV (deduced) 8 rGO–PVP NFs HI reduction (100°C, 1 h), electrospun R s = 17.0 Ω/sq; σ = 164.5 S/cm PV @0 V + reverse photoconductive D *: 3.6 × 10 10 (30 mW cm −2 ); 4.5 × 10 10 (15 mW cm −2 ) [ 19 ] on/off: 3.9 × 10 5 →1.5 × 10 6 RR: 1121 (dark) Φ B : 0.750→0.652/0.630 eV n : 1.60→3.92/4.43 Φ B (C–V): ~0.69 eV 9 Curcumin:rGO/Si Electrochemical reduction + codeposition E g ~ 3.41 eV Depletion built‐in field R : ~1.39 mA/W (max) [ 20 ] D *: ~5.5 × 10 8 Jones RR: 8.6094 × 10 4 V oc : 220–370 mV I sc : 0.48–12.18 µA EQE: 21% (365 nm); 14.6% (395 nm) Φ B (C–V): 0.96–1.04 eV 10 PVA‐rGO nanofibers/n‐Si Hydrazine reduction (95°C, 12 h), electrospun Depletion field; UV + IR R : 688 mA/W @365 nm [ 21 ] D *: 1.15 × 10 15 Jones on/off: 2.49 × 10 6 RR: ~2.4 × 10 6 V oc : ~0.4 V EQE: 234% (reported) Φ B ~ 0.81 eV n ~ 1.94 11 Pd‐rGO‐Ti Thermal (Ar/H 2 , 200–1000°C) WF 4.9→4.5 eV; R s 2493.8→42.7 Ω/sq PTE (asymmetric contacts) Range: UV–THz (reported) [ 22 ] R V : 137–142 mV/W D *: 1.06–15.80 × 10 6 cm Hz 1 2 W −1 t r / t f : ~100–200 ms NEP: 0.02–0.49 × 10 −6 W Hz −1 2 12 CdS NRs/rGO Spin‐coat GO; reduce Ar/H 2 (450°C, 3 h) Raman I D / I G ≈1.72 Schottky + piezo‐phototronic Range: 365–1450 nm [ 23 ] R : 0.58 mA/W @365 nm D *: 7.2 × 10 11 Jones t r / t f : 1.3/1.7 ms I light / I dark : >10 5 I dark : ~10 pA Strain: ~11% R increase at 4% compressive strain 13 Au@rGO/GaN NRs EDA reduction (90°C, 5 h) + Au WF(rGO) ~4.80 eV Schottky + Au LSPR Range: UV–Vis (examples) [ 24 ] R : 33.40 A/W (0 V) t r / t f : 0.43/0.38 s (UV) 14 GaN/rGO:Ag NPs Spray + anneal 150°C (N 2 , 120 min) WF 4.66 eV; E g 0.42 eV; high traps p–n built‐in field + LSPR Range: 360–980 nm [ 25 ] R : 266 mA/W (UV max); 73 mA/W @565 nm; 17 mA/W (NIR min) D *: 2.62 × 10 11 Jones t r / t f : 0.68/0.70 s (UV); 0.68/1.07 s (Vis) RR: ~10 5 on/off: 7000/300/2 (UV/Vis/NIR, 0 V) n : ~4 15 Bi 2 Te 3 /rGO Hydrothermal in EG (200°C, 4.5 h) Raman I D / I G 0.91; residual O (XPS) PEC + rGO transport Range: 365–850 nm [ 26 ] R : 6.072 mA/W @365 nm D *: 2.406 × 10 10 Jones t r / t f : 29/68.8 ms I ph / I dark : 412 V oc : ~162 mV I ph : ≈90.58 µA 16 Free‐standing rGO film Thermal (Ar/H 2 , 200–1000°C, 3 h) I D / I G 1.8875→1.44; n‐type Hall; Rch 4251→54 Ω PTE self‐powered Range: UV–THz (reported) [ 27 ] R V : up to 87.3 mV/W D *: up to 4.23 × 10 6 cm Hz 1 2 W −1 t r / t f : 13.5–49.7 ms NEP: best 20 nW Hz −1 2 17 SnSe 2 ‐rGO/MoS 2 Solvothermal GO→rGO (EG, 180°C, 24 h) WF (lit.) ~4.7 eV; θ ~0.64 (traps) Built‐in potential heterojunction R : 13.75 A/W @900 nm; 2.63 A/W @650 nm [ 12 ] D *: 5.08 × 10 12 (900 nm); 1.05 × 10 12 (650 nm) t r / t f : ~110/110 ms 18 RGO‐MoS 2 /pyramid Si Two‐step anneal (280°C Ar→600°C Ar/H 2 ) rGO transport role (qual.); θ ~ 0.6 3D built‐in field (KPFM‐supported) Range: 350 nm–4.3 µm [ 28 ] R : 21.8 A/W @808 nm (100 nW) D *: 3.8 × 10 15 (808 nm); 2.04 × 10 12 (1310 nm); 1.83 × 10 12 (1550 nm) t r / t f : 2.8/46.6 µs KPFM Δ V : ~200 mV (vs ~ 80 mV) 19 MAPbBr 3 /N‐rGO Hydrothermal lysine (160°C, 6 h) E F ~ −4.4 eV (band discussion); N, doping (XPS) Strong coupling; bias‐driven (ohmic) R : 3.6 × 10 4 A/W [ 29 ] D *: ~0.98 × 10 12 Jones t r / t f : 30/100 ms EQE: ~0.9 × 10 5 % LDR: 94.4 dB Open in a new tab Abbreviations: μ, mobility; Φ B , Schottky barrier height; σ , conductivity; D *, specific detectivity (Jones); I dark , dark current; I on / I off or on/off, light/dark current ratio; R , responsivity; R s , sheet resistance; R c , contact resistance; R V , voltage responsivity; t r / t f , rise/fall time; V bi , built‐in potential; V oc / I sc , opencircuit voltage/shortcircuit current; and J sc / J photo , (photo)current density. “qual.” denotes qualitative evidence (the paper describes the effect but does not report a numerical value). “lit. means the value is taken from literature”. O/C is the oxygen‐to‐carbon atomic ratio (typically from XPS), used as a proxy for reduction level in GO/rGO. E g is the optical bandgap (usually extracted from absorption/Tauc analysis). Raman I D / I G is the intensity ratio of the D band to the G band, indicating defect/disorder level in (r)GO. R ch is the channel resistance (device resistance of the rGO conduction channel). EG refers to ethylene glycol (solvent in solvothermal synthesis). E F is the Fermi level (energy referenced to vacuum or band edges as stated in the source). LDR is the linear dynamic range (typically in dB), quantifying the range of incident power over which the photoresponse remains linear; NEP, noiseequivalent power; p, hole concentration; PSD, noise power spectral density; RR, rectification ratio; WF, work function. Among the most actively researched areas is the use of rGO‐based composite materials in optoelectronic devices, particularly photodetectors. The integration of rGO with various MOs, TMDCs, metal selenides, and perovskite materials has opened new avenues for constructing highly responsive and energy‐efficient devices. The role of rGO in such composites is multifaceted: it acts as a conductive channel, charge transport layer, or interfacial modifier, thereby enhancing light absorption, photocarrier separation, and charge transport, which are crucial for efficient photodetection. Despite the extensive body of literature on rGO‐based photodetectors, the development of high‐performance self‐powered photodetectors remains relatively limited. Self‐powered devices are those that can generate photocurrent without requiring an external power source, making them ideal for portable, wearable, or remote sensing applications. In this review, we aim to specifically highlight the recent progress in rGO‐based self‐powered photodetectors, focusing on composite systems that incorporate rGO with other semiconducting materials to achieve enhanced device performance. Although a large number of reviews have discussed 2D materials and photodetectors in general, the present review is intentionally narrowed and differentiated in scope and analysis. Rather than surveying broad 2D‐material photodetectors, we focus specifically on rGO‐integrated self‐powered photodetector architectures, where rGO is not merely an additive but a functionally active interfacial component that can tune junction energetics and carrier dynamics. In many device stacks, rGO's reduction level, oxygen functional groups, and defect density directly influences interface engineering, charge–transfer pathways, and energy‐band alignment, thereby controlling the builtin electric field, zero‐bias carrier separation, dark current, response speed, and operational stability. We synthesize performance trends and recurring limitations (such as trap‐mediated photogating, interfacial recombination, hysteresis, and bandwidth tradeoffs) across rGO‐coupled systems, including MOs, TMDCs, selenides, and perovskites. In this review, we provide a focused and integrated discussion of rGO‐based self‐powered photodetectors, emphasizing rGO's active role in controlling interfacial energetics and carrier extraction under zero bias. To highlight what is distinct about rGO‐integrated architectures, we compare device classes based on the coupled semiconductor family (MOs, TMDCs, selenides, and perovskites) and relate performance metrics to band alignment, charge–transfer pathways, and interface quality. Additionally, we adopt a mechanismfirst taxonomy (PV/PEC/PTE) and map each rGO‐based heterostructure to its dominant zero‐bias driving force, while noting multifunctional hybrids where secondary effects strengthen the primary mechanism. Below, we first summarize representative recent demonstrations and then use them to extract the broader design rules, performance trends, and recurring limitations of self‐powered operation. Some notable examples of such systems include rGO–MO heterojunctions, which exploit the internal electric field at the interface for effective carrier separation:ZrO 2 –rGO nanocomposites demonstrating improved photoconductivity under UV illumination [ 16 ]. rGO–ZnO nanorod arrays, which exhibit enhanced charge transfer and stability under solar irradiation [ 30 ]. Ag/rGO hybrid structures integrated with plasmon‐enhanced SnO 2 , yielding increased responsivity through localized surface plasmon resonance (LSPR) effects [ 17 ]. Additionally, rGO–TMDC heterostructures, which benefit from the synergistic interaction between 2D‐layered materials such as SnSe 2 –rGO bulk heterojunctions, enable broadband photodetection with excellent light absorption and carrier mobility [ 12 ]. RGO–MoS 2 /Pyramid Si heterojunctions, which leverage the multi‐interface charge dynamics for enhanced self‐powered operation [ 28 ]. Likewise, rGO–perovskite composites, known for their strong light‐harvesting capabilities and tunable bandgaps, for instance, perovskite/N‐doped rGO hybrids, demonstrate increased stability and improved carrier extraction in photodetector applications [ 29 ]. rGO/halide perovskite composites, such as laser‐rGO LSG/CsPbBr 3 , where the rGO matrix enhances charge mobility and reduces trap states [ 13 ]. CsPbI 3 , graphene, and poly(vinylidene fluoride‐trifluoroethylene) CsPbI 3 /rGO/P(VDF‐TrFE) composites, which utilize ferroelectric effects and rGO‐mediated conductivity to improve photodetection performance under ambient conditions [ 31 ]. These examples illustrate the vast potential of rGO‐based materials in next‐generation photodetector technologies, particularly in enabling self‐powered operation. The heterojunction engineering, band alignment, and interface optimization between rGO and its conjugate materials are key factors that govern the efficiency of charge separation and transport. In this review, we provide a comprehensive overview of the current advancements in rGO‐based self‐powered photodetectors, classifying them according to the types of secondary materials (MOs, TMDCs, selenides, and perovskites) with which rGO is coupled. Furthermore, we delve into the challenges associated with these devices, such as interfacial recombination, material compatibility, environmental stability, and scalability for industrial production. Finally, we outline the prospects and potential strategies for overcoming these limitations, aiming to pave the way toward the realization of commercially viable, energyefficient, and miniaturized photodetection systems. 2. Conceptual Framework for rGO‐Based Self‐Powered Photodetectors Self‐powered photodetectors based on rGO can be organized along two complementary axes: (i) the operating mechanism that enables zerobias photocurrent generation and (ii) the material stack or heterojunction geometry that implements that mechanism in practice. In this review, we use a mechanismfirst framework, classifying devices into PV, photoelectrochemical (PEC), and photothermoelectric (PTE) architectures, and then mapping each rGO‐based heterostructure to the most physically appropriate class. Because many modern stacks intentionally combine multiple internal driving forcesbuiltin fields, polarization, strain, photogating, and thermal gradients. We also identify multifunctional hybrids where a dominant mechanism is strengthened by a secondary control channel. 2.1. Photovoltaic Architectures In PV architectures, a built‐in electric field at a solid‐state junction (Schottky, p–n, or p–p) separates photogenerated electron–hole pairs and drives them toward opposite electrodes at zero external bias. In rGO‐based devices, this internal field is typically engineered through workfunction tuning, interfacial dipoles, depletion control, and deliberate management of trapmediated photogating. Most rGO‐based self‐powered photodetectors discussed in this review fall within this PV class. 2.2. rGO/Si and rGO/Oxide‐Si Heterojunctions A large and technologically important family exploits junctions between rGO (or rGO‐based nanofibers/composites) and crystalline silicon, sometimes with an oxide or organic interlayer to tune band alignment and suppress interfacial recombination. The rGO/p‐In 2 Se 3 /n‐Si trilayer is a representative vertical PV stack in which the builtin field is distributed across the p‐In 2 Se 3 /n‐Si junction and the rGO contact, enabling self‐powered broadband response [ 32 ].The classic rGO/n‐Si p–n heterojunction similarly uses rGO as a conductive, work‐functiontunable p‐type layer on n‐Si, producing strong internal fields and high zerobias responsivity [ 18 ]. Structuring rGO into high‐area networks can amplify junctiondriven separation; for example, electrospun rGO/polyvinyl pyrrolidone (PVP) nanofibers on n–Si behave as a textured p–n architecture where the rGO–polymer network increases junction area, strengthens depletion‐driven separation, and supports high rectification and EQE in the self‐powered regime [ 19 ]. Interlayers and composite shells are frequently used to improve optical coupling and interfacial electronic quality. ZrO 2 ‐rGO/n‐Si nanofiber heterojunctions combine a wide‐bandgap transparent oxide with rGO to form a composite p‐type network on n‐Si, and the resulting interfacial field drives UV‐dominant PV response with high detectivity [ 16 ]. PVA‐rGO/n‐Si nanofiber devices follow a related strategy where a polymer–rGO composite forms a conformal p‐type coating on n‐Si, again operating as a depletion‐driven PV junction with strong zerobias figures of merit [ 21 ]. Organic additives can also introduce gain channels without changing the PV backbone; in curcumin:rGO/n‐Si, curcumin contributes dipoles and trap states, so the device remains fundamentally PV while photogatinglike effects can enhance gain, often at the cost of slower dynamics [ 20 ]. In addition to direct rGO/Si junctions, the review also covers silicon‐based PV stacks where rGO couples Si to a second absorber or transport layer. For example, the rGO/MoS 2 /pyramid‐Si architecture is best understood as a PV device in which pyramid texturing enhances light trapping, while rGO and MoS 2 improve interfacial extraction and bandoffset‐assisted separation at zero bias [ 28 ]. Across these Si‐based systems, the dominant mechanism is PV: rGO primarily acts as a tunable workfunction contact, a lateral transport layer, and an interfacial ‘quality controller’ through dipole formation and trap management. These devices are therefore directly comparable to graphene/Si Schottky photodetectors that serve as established solid‐state PV self‐powered baselines [ 30 ]. They also retain practical relevance for device integration and processing in silicon compatible platforms [ 10 ]. In particular, the ability to engineer barrier heights and depletion fields at graphene‐family/Si interfaces is well established [ 11 ]. 2.3. rGO/Metal Oxide and rGO/Chalcogenide Heterojunctions In this group, rGO is combined with wide bandgap oxides or chalcogenides to form Schottky like or p–n junctions. The built in potential is typically established at the oxide–rGO interface (or across a composite network), and defect states can introduce photogating contributions that enhance gain while trading off response speed [ 1 ]. Thermally reduced rGO–ZnO hybrid nanostructures are representative PV junctions in which thermal treatment reduces GO to rGO while simultaneously modifying ZnO and the rGO/ZnO interface to support diodelike self‐powered operation [ 33 ]. BaTiO 3 /rGO (BTO/rGO) heterostructures remain PV at their core, but ferroelectric polarization can further modulate the internal junction field and strengthen zerobias separation [ 34 ]. Plasmon or metal assisted oxide/rGO designs still map naturally onto PV operation when the decisive driving force remains the junction field. In the Ag/rGO‐SnO 2 plasmon‐enhanced oxide composite discussed in this review, optical enhancement can increase carrier generation, but the zero‐bias photocurrent is ultimately collected through the builtin field at the rGO/oxide interface [ 17 ]. Chalcogenide/rGO junctions in this subsection are also dominantly PV. In Se/rGO p–p heterojunctions, asymmetric work functions and interfacial band bending generate a builtin potential that drives broadband self‐powered response with fast dynamics [ 15 ]. In CdS nanorod array/rGO devices, the rGO/CdS interface operates as a PV junction, while the piezoelectric nature of CdS enables straintunable modulation of depletion and band alignment (piezo‐phototronic control) on top of the PV baseline. More broadly, many oxide/chalcogenide‐rGO stacks exhibit trap‐assisted photogating as an auxiliary gain mechanism that must be balanced against speed and stability [ 23 ]. Recombination pathways in optoelectronic devices are determined by the interplay between intrinsic band to band processes and extrinsic defect mediated channels, where defect assisted losses often surpass intrinsic recombination and dominate device behavior under operating conditions. Bulk and interfacial recombination processes critically determine charge carrier dynamics and thus the overall performance of semiconductor and rGO hybrid optoelectronic devices. In semiconducting layers, bulk recombination is predominantly governed by Shockley Read Hall mechanisms arising from deep and shallow defect states within the bandgap, which reduce minority carrier lifetimes and diffusion lengths, leading to enhanced dark current and voltage losses. Numerical and experimental studies by Sherkar et al. have shown that bulk defect densities on the order of 10 15 –10 17 cm −3 can reduce carrier lifetimes by more than an order of magnitude, directly impacting open circuit voltage and fill factor [ 35 ]. At rGO semiconductor junctions, interface recombination becomes particularly severe due to the presence of interfacial trap states associated with residual oxygen functional groups, lattice mismatch, and chemical disorder. First principles calculations (DFT) by Gillespie and Martsinovich demonstrate that epoxy and hydroxyl groups at TiO 2– rGO interfaces introduce localized mid gap states that act as efficient electron traps, facilitating non radiative recombination and Fermi level pinning [ 36 ]. Experimentally, this manifests as suppressed photovoltage and reduced charge extraction efficiency, with studies reporting order of magnitude increases in dark current when interface trap densities are not adequately controlled [ 37 ]. Furthermore, trap‐assisted recombination is strongly exacerbated by oxygen functional groups, carbon vacancies, and grain boundaries within rGO and polycrystalline semiconductor films. Oxygen‐related defects disrupt the sp 2 network in rGO, generating localized states that enable multistep capture emission processes, while vacancies and grain boundaries serve as recombination hot spots that dominate under low to moderate injection conditions [ 38 ]. Collectively, these findings emphasize that minimizing bulk defect density, passivating rGO semiconductor interfaces, and controlling oxygen functionalization and microstructural disorder are essential to suppress recombination losses and approach intrinsic performance limits in rGO‐based hybrid devices. 2.4. Moderate Trap Densities can Enhance Photogain via Carrier Trapping Moderate trap densities can beneficially enhance photogain in photoconductive and hybrid optoelectronic devices by prolonging the effective lifetime of one type of photogenerated carrier while allowing the opposite carrier to circulate multiple times through the external circuit. In this regime, traps originating from surface states, oxygen functional groups, vacancies, or shallow grain boundary defects temporarily immobilize minority carriers (often holes), thereby suppressing recombination and extending the lifetime. Studies on rGO and TMDC hybrid photodetectors report responsivities exceeding 10 3 –10 5 A W −1 under moderate trap densities, where trapping‐induced photogain outweighs mobility loss [ 39 ]. However, this work consistently shows that excessive trap densities eventually become detrimental, leading to slow response times, hysteresis, and enhanced dark current. Therefore, an optimal, moderate trap density represents a performance sweet spot in which controlled trapping enhances photogain without severely compromising speed or noise, highlighting the dual and nonmonotonic role of defects in photodetector operation. 2.5. Excessive Defects Increase Dark Current and Slow Response Times Excessive defect densities are widely recognized as a major limitation to optoelectronic device performance, as they simultaneously increase dark current and severely slow temporal response through enhanced trap‐assisted transport and recombination pathways. In rGO and graphene hybrid photodetectors, residual oxygen groups and vacancy clusters have been shown to act as long‐lived trapping centers that trap one carrier species while the opposite carrier circulates, producing slow rise and fall times despite high apparent photogain [ 38 ]. Singh et al. found that poorly controlled oxygen related interfacial trap states lead to an ≈ 25 fold increase in dark current, rising from 20 nA to 496 nA, highlighting the critical role of interfacial trap in governing leakage behavior [ 37 ]. Moderate trap densities may enhance photogain, but excessive defects shift device operation into a regime dominated by leakage current, slow detrapping kinetics, and degraded signal to noise ratio, underscoring the necessity of stringent defect control and interface passivation to achieve low noise, fast response optoelectronic devices. 2.6. Reduction Induced Trap Passivation Improves Detectivity and Speed Reduction induced trap passivation is a critical strategy for simultaneously improving detectivity and dynamic response in rGO based and hybrid semiconductor photodetectors, as it directly suppresses deep trap states responsible for dark current leakage and slow carrier detrapping. Controlled chemical or thermal reduction of GO partially removes oxygen functional groups (epoxy, hydroxyl, and carbonyl species) that disrupt the sp 2 network and introduce mid gap trap states, thereby lowering trap density while restoring carrier mobility. Experimental studies show that optimized reduction leads to a substantial decrease in dark current often by one to two orders of magnitude resulting in enhanced specific detectivity due to reduced noise current while simultaneously accelerating rise and decay times by mitigating long lived trapping and persistent photoconductivity. Chang et al. showed that tuning the reduction conditions of GO enables controlled modulation of oxygen functional groups and vacancy like structural defects in rGO, which directly governs infrared optoelectronic transport and photocurrent generation. Notably, rGO‐based photoconductors exhibited an external responsivity of ≈ 0.7 A W −1 , exceeding that of pristine graphene by more than an order of magnitude, underscoring the beneficial role of defect mediated photogain [ 40 ]. For instance, Minitha et al. demonstrated that progressive reduction of GO systematically decreases oxygen related trap density, yielding improved conductivity and faster photoresponse [ 38 ]. From a theoretical perspective, first principles studies by Gillespie and Martsinovich show that removal of specific oxygen moieties at rGO semiconductor interfaces eliminates localized mid gap states, thereby suppressing interface recombination and trap‐assisted transport. Collectively, these works establish that while moderate trapping can enhance photogain, reduction‐induced passivation shifts device operation toward a low noise, fast response regime by suppressing deep traps, enabling high detectivity without sacrificing bandwidth an essential requirement for practical, high speed optoelectronic applications. 2.6.1. rGO/TMDC and Multi‐Component Bulk Heterojunctions Layered semiconductors (TMDCs and related materials) combine strong light absorption with tunable bandgaps, making them natural partners for rGO‐based extraction networks and interface engineering [ 41 ]. In these stacks, self‐powered behavior typically follows from type II band alignment and depletion fields across multiple interfaces. The SnSe 2 ‐rGO/MoS 2 /Si bulk heterojunction is a representative multi‐interface PV architecture in which layered SnSe 2 , rGO, and MoS 2 are integrated on Si, and charge separation is strengthened by the combined band offsets across rGO–TMDC interfaces and the TMDC/Si junction. Other rGO/TMDC devices discussed in the review (for example, MoS 2 or MoSe 2 ‐based hybrids) likewise rely on type‐II alignment at rGO/TMDC junctions, with defect‐assisted photogating often acting as an added gain channel [ 12 ]. 2.6.2. rGO/Perovskite and Ferroelectric Composites Perovskite–rGO devices in this review primarily function as PV photodiodes where the perovskite is the main absorber and rGO serves as a transparent electrode or extraction/transport layer that suppresses interfacial recombination and improves carrier collection. A key multifunctional example is CsPbI 3 /rGO/P(VDF‐TrFE), where the device remains fundamentally PV, while ferroelectric polarization provides an internal field modulation handle that can tune responsivity and detectivity at zero bias [ 8 ]. The review also includes perovskite/rGO variants where rGO is intentionally modified; in perovskite/N‐doped rGO stacks, doping shifts rGO's work function and interfacial energetics, thereby influencing barrier heights, depletion widths, and builtin field strength [ 19 ]. 2.6.3. rGO with GaN and Other Semiconductors Several high‐performance UV to broadband devices combine rGO with GaN and related wide bandgap semiconductors. In these stacks, the GaN/rGO interface is best described as a Schottky like PV junction whose builtin field drives self‐powered operation [ 24 ]. In Au@rGO/GaN heterostructures, plasmonic Au nanoparticles (NPs) extend the spectral response toward the visible through local field enhancement and hot‐carrier processes, while the separating and collecting force remains the junction field at the GaN/rGO interface [ 24 ]. In GaN/rGO designs incorporating plasmonic Ag NPs and transparent Au nanowire electrodes, the same PV backbone is retained, with plasmonic elements mainly acting to improve absorption and carrier generation [ 25 ]. 2.6.4. Pure rGO Thin‐Film Architectures A smaller but conceptually important category involves rGO devices without a conventional semiconductor junction. Freestanding rGO membranes discussed in this review can generate a self‐powered response through internal potential gradients, contact asymmetry, and defect controlled transport within the rGO network [ 27 ].Because such devices can show mixed signatures (photoconductive, PVlike, and thermoelectric), they are best interpreted as junction‐free architectures where builtin lateral fields and nonuniform carrier landscapes provide the dominant zero‐bias driving force [ 27 ]. 2.6.5. Photoelectrochemical Architectures In PEC architectures, the active junction is formed at the semiconductor electrolyte interface, and photocurrent is generated through light‐driven redox processes. rGO typically improves charge transport, suppresses recombination, and can broaden absorption by acting as a conductive, optically active partner. The review includes a WS 2 ‐rGO photoanode in aqueous electrolyte as a representative PEC self‐powered detector, where separation is driven by the semiconductor electrolyte interfacial potential and rGO provides a fast extraction pathway that improves zero‐bias photocurrent [ 14 ]. A second PEC example is the Bi 2 Te 3 /rGO topological‐insulator heterojunction used for broadband self‐powered PEC photodetection, where Bi 2 Te 3 serves as a narrow bandgap absorber and rGO contributes conductivity and broadband optical response [ 26 ]. 2.6.6. Photothermoelectric Architectures PTE architectures exploit light‐induced temperature gradients to generate photovoltage via the Seebeck effect. rGO is well suited for PTE operation when combined with asymmetric contacts, suspended geometries, or hybrid absorbers that localize heating [ 22 ]. The laser‐scribed rGO/CsPbBr 3 (LSG/CsPbBr 3 ) composite discussed in this review is treated as a flexible ultra‐broadband device where laser‐scribed rGO forms a thermoelectric network and CsPbBr 3 nanocrystals act as strong absorbers; while PV contributions can coexist, the geometry‐dependent photovoltage supports a substantial PTE component [ 13 ]. The suspended Pd‐rGO‐Ti device is a clearer PTE architecture, where asymmetric contacts and a suspended rGO bridge are deliberately used to maximize thermal gradients and Seebeck asymmetry, producing zero‐bias photovoltage primarily through the PTE effect [ 22 ]. Freestanding rGO membranes can also exhibit strong PTE signatures because substrate‐free geometries enhance heating and reduce dielectric screening [ 27 ]. 2.6.7. Piezo‐Phototronic and Multifunctional Hybrid Architectures Some devices intentionally integrate mechanical degrees of freedom or ferroelectric polarization with PV operation, creating a tunable modulation channel for band alignment, depletion width, and internal field strength. In CsPbI 3 /rGO/P(VDF‐TrFE), ferroelectric polarization provides internal‐field modulation on top of a PV baseline, enabling multifunctional operation (for example, combined pressure and light sensing) without losing self‐powered PV separation [ 31 ]. In CdS nanorod array/rGO stacks, strain can tune depletion and band offsets at the CdS/rGO interface through the piezo‐phototronic effect, while the underlying self‐powered mechanism remains PV [ 23 ]. In many ferroelectric oxide/rGO systems, polarization similarly acts as a practical handle to strengthen or tune the builtin PV field [ 34 ]. 2.6.8. Architectures Outside the rGO‐Based Classification For completeness, the review also cites nonrGO benchmark devices that are useful baselines but fall outside the strict rGO‐based map. Graphene/Si (Gr/Si) Schottky photodetectors are self‐powered PV devices that use pristine graphene instead of rGO as the transparent electrode on Si [ 42 ]. Pioneering work by Periyanagounder et al. demonstrated the potential of Gr/Si van der Waals heterostructures for self‐powered photodetection, showing Schottky‐junction behavior with a barrier height of 0.76 eV, high responsivity (510 mA/W), fast response time (130 μs), and an on/off ratio of 10 5 , consistent with efficient photocarrier separation at the 2D/3D interface [ 43 ]. Perovskiteonly photodetectors without rGO are included as reference points to contextualize what rGO contributes to interfacial recombination control and charge extraction [ 44 ]. 2.7. rGO/Metal Oxide‐Based Self‐Powered Photodetectors The fabrication of high‐performance optoelectronic devices, particularly photodetectors, fundamentally relies on the use of materials that exhibit excellent charge carrier mobility. Efficient carrier transport is essential because, during photo‐excitation, the absorption of light by the photoactive material leads to the generation of electron–hole pairs. For a measurable photocurrent or photo‐voltage to be produced, these photo‐generated charge carriers must be rapidly and effectively separated and transported to the device electrodes. However, if the carrier mobility within the photoactive layer is insufficient, there is a high probability that the electrons and holes will recombine before reaching the electrodes, thereby diminishing the device performance or entirely quenching the photocurrent. To mitigate this issue, modern photodetector architectures often incorporate auxiliary transport layers, namely electron transport layers and hole transport layers. These functional layers serve to selectively extract and transport electrons and holes, respectively, while also acting as barriers to prevent recombination at the interface. The inclusion of such transport layers is particularly critical in multilayer or hybrid device configurations where the photoactive material alone cannot ensure adequate charge extraction efficiency. Nonetheless, even with such engineered layers, the interfacial recombination of photo‐generated carriers within or at the boundary of the photoactive material remains a significant challenge. This necessitates the incorporation of additional supporting materials that can complement the optoelectronic functionality of the primary active layer. In this context, MOs have emerged as outstanding candidates due to a confluence of desirable properties. MOs such as ZnO, SnO 2 , TiO 2 , Ga 2 O 3 , In 2 O 3 , and indium tin oxide (ITO) possess inherently high electron mobility, which facilitates rapid transport of photogenerated carriers. Notably, many of these oxides maintain efficient charge transport characteristics in both their amorphous and crystalline phases, which is advantageous for scalable and low‐temperature fabrication processes. Beyond their excellent charge transport behavior, MOs offer additional benefits, including mechanical robustness and environmental stability, enabling device longevity and resistance to physical stress [ 45 ]. Wide bandgap and high optical transparency of MOs ensure minimal interference with incident light and maximizes photon absorption in the underlying photoactive layer. Finally, its compatibility with a wide range of photoactive materials, both organic (e.g., polymers, small molecules) and inorganic (e.g., perovskites, quantum dots), facilitating their integration into diverse device architectures. As a result, MOs are not only used as charge transport layers, but also frequently serve as interfacial layers, barrier layers, and even photoactive components in UV photodetectors. Their tunable surface properties and facile processability make them highly suitable for applications in flexible, transparent, and self‐powered photodetector technologies. Zhan et al . developed a self‐powered visible‐light photodetector using thermally reduced rGO–ZnO hybrid nanostructures [ 33 ]. The device operates without external bias, functioning like a PV cell. Thermal treatment simultaneously reduces GO to rGO and carbon‐dopes ZnO, enhancing its visible‐light photo‐response. ZnO is typically used for designing UV photodetectors, and it is not efficient in the visible region due to the wide band gap. There are countless reports to transform its optical absorption from UV to the visible region. Zhan et al . successfully demonstrated the transformation by incorporating rGO into ZnO nanostructures that facilitates charge transfer from rGO to carbon‐doped ZnO. They have used a very simple method of photodetector device fabrication by spin coating rGO–ZnO nanostructures in isopropanol on a silicon substrate. The substrates were patterned with gold electrodes (20 nm Ti/200 nm Au) for making electrical contacts. Similarly, Liu et al . reported a hybrid nanostructure composed of a ZnO nanowire array and a rGO film, which demonstrated enhanced PV response from the visible to near‐infrared (NIR) range [ 22 ]. Compared to pure ZnO or rGO alone, the hybrid showed significantly faster and stronger broadband photoresponse, attributed to the formation of interfacial Schottky junctions between ZnO and rGO. With the combination of rGO, they have achieved a PV responsivity of 0.55 mV/W, which is much higher than 0.07 mV/W for only ZnO nanowires. The required rGO was deposited using the electrophoresis technique with two‐electrode system of ITO‐coated glass covered by ZnO nanowires. 2.8. rGO/TMDC‐Based Self‐Powered Photodetectors TMDCs, such as MoS 2 , WS 2 , SnS 2 , and SnSe 2 , have recently attracted significant attention in the field of materials science due to their exceptional photophysical properties. These materials exhibit high charge carrier mobility, tunable bandgaps dependent on their layer thickness, and ease of heterostructure fabrication. These advantages make TMDCs highly suitable for a wide range of advanced applications including optoelectronic devices [ 8 ], photocatalysis [ 47 ], energy storage systems [ 48 ], field‐effect transistors (FETs) [ 49 ], and chemical or biological sensors [ 50 ]. Among TMDCs, molybdenum disulfide (MoS 2 ) stands out as a particularly promising candidate for next‐generation optoelectronic applications. MoS 2 offers a high carrier mobility of ≈ 500 cm 2 V −1 s −1 and covers a broad light absorption range from 350 nm to 950 nm [ 51 , 52 ]. Structurally, MoS 2 exists in layered forms and can be exfoliated down to monolayers or even synthesized as NPs and 2D sheets. One of its unique features is the dimensionality‐dependent electronic bandgap: monolayer MoS 2 exhibits a direct bandgap of ~1.8 eV, while multilayer MoS 2 exhibits an indirect bandgap of ~1.3 eV [ 53 ]. This tunable bandgap property allows for precise control over optical and electronic behavior, making MoS 2 an ideal material for designing high‐performance photodetectors and other optoelectronic devices. Similarly, tungsten disulfide (WS 2 ) has emerged as another promising TMDC for self‐powered and energy‐efficient photodetection systems. In a study conducted by Tao et al. (2019), a novel hybrid nanostructure comprising WS 2 nanosheets (NS) and rGO was developed to fabricate a self‐powered photoanode for PEC photodetectors. The synthesis involved a two‐step process: first, WS 2 NSs were prepared via lithium‐ion intercalation followed by exfoliation; then, these NSs were combined with GO and subjected to hydrothermal reduction to obtain the WS 2 –rGO hybrid material as shown in Figure 1a . FIGURE 1. Open in a new tab (a) Schematic illustration of the hydrothermal synthesis process of the WS 2 –rGO hybrid. (b) Photoresponse of the WS 2 –rGO hybrid under varying light intensities, measured at a constant bias voltage of 0.5 V. (c) Light conversion efficiency of the WS 2 –rGO hybrid as a function of irradiation intensity, along with the corresponding fitting curve. Reproduced with permission from [ 14 ] Copyright 2019, Springer Nature. Unlike traditional photodetectors that rely on FET architecture, the PEC device designed by Tao et al. utilizes a semiconductor–electrolyte interface to drive photo‐induced electrochemical reactions. The built‐in potential at this interface enables efficient charge separation of photo‐generated electron–hole pairs. The incorporation of rGO plays a crucial role by providing high‐conductivity pathways that facilitate fast charge transport and significantly suppress recombination losses. The photocurrent performance of the WS 2 –rGO photo‐anode was benchmarked under different conditions. At zero bias, the WS 2 –rGO device showed a significantly higher photocurrent compared to pristine WS 2 NSs, highlighting the synergistic effect of the hybrid structure. Moreover, the photocurrent remained stable during repetitive light‐on/off cycles at a 10‐second interval, demonstrating excellent operational stability and fast response. Interestingly, when an external bias was applied (up to 0.8 V), the photocurrent of the WS 2 –rGO composite showed a substantial increase, about 200% compared to the zero‐bias condition. This enhancement was attributed to the additional electric field, which further assists in separating and transporting charge carriers. The study also presented a spectral photocurrent analysis as a function of applied bias, revealing an exponential rise in current from 0.24 to 4.32 μA cm −2 , indicating strong photoelectric conversion efficiency under increasing external potentials. Additionally, cycling durability tests confirmed the robustness of the WS 2 –rGO composite. The device retained its performance over 100 operational cycles with negligible degradation, confirming its potential for long‐term use in practical optoelectronic systems. The authors concluded that the integration of rGO significantly improves carrier separation and minimizes recombination, thereby enhancing the overall efficiency and durability of the PEC photodetector [ 14 ]. Figure 1b indicates the photoresponse of the WS 2 –rGO hybrid under varying light intensities. It showed maximum photoresponse at 150 mW of light irradiation. The corresponding photocurrent density as a function of power density is shown in Figure 1c . This study exemplifies how hybridizing TMDCs with conductive carbon‐based materials like rGO can significantly advance the design of efficient, self‐powered photodetectors for next‐generation technologies. A notable advancement in the field of rGO‐based self‐powered photodetectors was introduced by Kumawat et al . in 2021 [ 12 ], who developed a bulk heterojunction photodetector combining SnSe 2 , rGO, and MoS 2 . This innovative design harnesses the synergistic properties of these layered 2D materials to fabricate a high‐performance, broadband self‐powered photodetector. The device architecture is strategically engineered for efficient photoresponse and autonomous operation. The fabrication process involves two key steps: synthesis of SnSe 2 –rGO composite NSs via a solvothermal route, resulting in a homogenous dispersion of rGO within SnSe 2 . Deposition of a MoS 2 thin film onto a silicon substrate using pulsed laser deposition (PLD) ensures high‐quality, uniform films with excellent adhesion and crystallinity. Following synthesis, the SnSe 2 –rGO composite is drop‐cast onto the predeposited MoS 2 layer, forming a multicomponent heterojunction on the Si substrate, Figure 2a . Though the fabrication process is relatively sophisticated, requiring precise control during solvothermal synthesis and PLD, the resulting tri‐layered heterostructure presents exceptional advantages for optoelectronic applications. SnSe 2 is known for its high optical absorption coefficient (>10 4 cm −1 ) and thickness‐dependent bandgap, which makes it ideal for harvesting light over a broad spectrum. As evident from Figure 2b , the device showed significant responsivity over a range of wavelengths, though a maximum responsivity was observed at around 900 nm. The corresponding optical absorbance is shown in Figure 2c . rGO, with its high conductivity and large surface area, functions as a rapid charge transport medium while also helping to suppress electron–hole recombination. MoS 2 , a well‐known TMDC, contributes high carrier mobility and strong absorption in the visible to NIR regions. The crux of the device's performance lies in the favorable band alignment and built‐in electric field at the SnSe 2 –rGO/MoS 2 interface, which drives efficient charge separation even in the absence of an external bias, as shown in Figure 2d , which is a key requirement for self‐powered operation. The interpenetrating network of SnSe 2 and rGO enhances the interfacial contact area, thereby shortening the exciton diffusion length, increasing the rate of carrier separation, and facilitating efficient charge transport to the electrodes. FIGURE 2. Open in a new tab (a) SnSe 2 – rGO/MoS 2 device configuration. (b) Responsivity vs wavelength of the device. (c) Absorbance spectrum of SnSe 2 –RGO composite, (d) I–V characteristics under dark and 900 nm light irradiation. Reproduced with permission from [ 12 ] Copyright 2021, American Chemical Society. These structural advantages culminate in a broadband photoresponse ranging from ultraviolet (UV) to NIR regions. Experimental results show a strong photocurrent response, particularly at 900 nm, where the responsivity peaks, correlating well with the material's absorption spectrum. Responsivity was measured across 300–1100 nm under zero bias conditions, demonstrating the true self‐powered nature of the device. The I – V characteristics under 900 nm illumination revealed a sharp increase in photocurrent at 0 V, confirming the effectiveness of the built‐in electric field for carrier separation without any external power source. The device also showed excellent spectral coverage, high sensitivity, and potential for low‐power, large‐area photodetection applications. Quantitative parameters explicitly reported alongside the schematic Figure 3a enable a first‐pass band alignment map for the SnSe 2 –rGO/MoS 2 device. The authors adopt literature work functions of Φ(RGO) ≈ 4.7 eV, Φ(SnSe 2 ) ≈ 4.8 eV, and Φ(MoS 2 ) ≈ 4.2 eV (energies referenced to vacuum), implying a ~0.5–0.6 eV work‐function mismatch between MoS 2 and the donor components (SnSe 2 /rGO). Upon contact, the Fermi level equilibrates and the resulting band bending/built‐in potential across the interpenetrating SnSe 2 –rGO network drives exciton dissociation and carrier drift in the absence of external bias. Under illumination, photons are absorbed in SnSe 2 ( E g ≈ 0.92 eV) and MoS 2 ( E g ≈ 1.3 eV), creating excitons that diffuse to the bulk heterojunction and separate via the built‐in field; the band alignment is described as energetically favoring carrier transport toward the electrodes, Figure 3b . Consistent with this picture, at zero external bias under 900 nm irradiation, the SnSe 2 –rGO/MoS 2 heterostructure shows a responsivity of 5.62 A W −1 , which is 216× higher than the corresponding rGO/MoS 2 device (0.026 A W −1 ). At 650 nm (0.075 mW cm −2 , zero bias), the reported responsivity and detectivity are 2.63 A W −1 and 1.05 × 10 12 Jones, with rise/decay times of 106/106 ms. FIGURE 3. Open in a new tab (a) Energy band diagram of SnSe 2 ‐RGO/MoS 2 device. (b) Schematic showing charge carrier separation process at the bulk heterojunction. Reproduced with permission from [ 12 ]. Copyright 2021, American Chemical Society. Despite the somewhat complex fabrication methodology, the study underscores the immense potential of combining SnSe 2 , rGO, and MoS 2 to design next‐generation, self‐powered photodetectors. The approach not only offers a scalable pathway to broadband, energy‐efficient devices but also exemplifies how the judicious combination of 2D materials with complementary electronic and optical properties can yield high‐performance optoelectronic platforms. 2.9. rGO/Perovskite‐Based Self‐Powered Photodetectors rGO and perovskite‐based materials have emerged as key building blocks for the development of next‐generation self‐powered photodetectors, offering a compelling combination of efficiency, versatility, and sustainability in light detection technologies [ 54 ]. These materials, when strategically combined, give rise to synergistic properties that significantly enhance the optoelectronic performance of devices without the need for external power sources. Halide perovskites, notably those based on lead halides, are well‐known for their exceptional optoelectronic properties, including high absorption coefficients, long carrier diffusion lengths and lifetimes, bandgap tunability across the visible spectrum, and solution‐processability for low‐cost fabrication. Incorporating rGO into perovskite structures serves multiple functions: it enhances carrier mobility, reduces trap‐state recombination due to its high electrical conductivity, and aligns favorably in terms of work function, thereby facilitating efficient charge extraction at the interface [ 55 ]. This combination is particularly advantageous in PV‐mode photodetectors, where built‐in electric fields, rather than external biases, are responsible for charge separation and transport [ 56 ]. Typical rGO/perovskite heterojunctions exploit vertical or lateral designs and often incorporate asymmetric metal contacts or interfacial engineering techniques to maximize responsivity and detectivity under self‐powered operation [ 57 ]. A pioneering example was demonstrated by Li et al., who reported a flexible, self‐powered ultra‐broadband photo‐thermoelectric photodetector based on a laser‐scribed rGO/CsPbBr 3 (LSG/CsPbBr 3 ) composite [ 13 ]. In this method, rGO was produced during the device fabrication process. For that, they have deposited GO on cleaned PET substrate by spin coating and allowed it to dry at room temperature. After that, a 450 nm laser was used for the reduction of GO to rGO. To control the degree of reduction, the power of the laser was changed from 237.5, 208.4, 204.2, 200, to 196 mW. This process is termed as photothermal effect, where GO converts light absorption into heat and eliminates its oxygen‐containing functional groups, resulting in the formation of rGO. Afterwards, CsPbBr 3 crystal was spin‐coated over the rGO layer. For electrical contacts, gold electrodes were thermally evaporated using a shadow mask with a channel width of 100 μm and a channel length of 2.5 mm. The unique combination of thermoelectric and photoelectric effects allowed the device to exhibit a broad photoresponse ranging from UV to terahertz (THz) wavelengths at room temperature, an unprecedented spectral range for a single material system. Figure 4b provides the quantitative band‐alignment inputs for the rGO/perovskite heterojunction: Φ(Au) ≈ 5.1 eV and Φ(LSG) ≈ 4.6 eV, while CsPbBr 3 has CBM ≈ 3.6 eV and VBM ≈ 5.9 eV (thus χ ≈ 3.6 eV and E g ≈ 2.3 eV). Schottky–Mott estimates then give electron barriers Φ Bn (LSG/CsPbBr 3 ) ≈ 1.0 eV and Φ Bn (Au/CsPbBr 3 ) ≈ 1.5 eV, and hole barriers Φ Bp (LSG/CsPbBr 3 ) ≈ 1.3 eV and Φ Bp (Au/CsPbBr 3 ) ≈ 0.8 eV. Upon contact, Fermi‐level equilibration implies band bending at each interface, defining the carrier‐selective injection/extraction landscape. Figure 4a,c–g further show that the self‐powered signal is dominated by the PTE mechanism: local laser heating creates a spatial temperature gradient (Δ T ), producing a finite V PTE (ΔV PTE in the I–V curves) and a prompt Δ I response at zero external bias. This example therefore links quantitative Φ/χ/band‐edge positions and expected barriers to zero‐bias carrier separation, while emphasizing that misalignment (larger opposing barriers or weaker internal driving force) would promote recombination‐dominated behavior. The device achieves broadband detection (405 nm to 118 μm) with responsivity of 135 mA/W (UV) and 10 mA/W (THz) at zero bias, with fast response time (18 ms). FIGURE 4. Open in a new tab (a) Mechanism schematic for PTE effect; (b) schematic of photocurrent generation process of the device; (c) temperature profile of active location under dark and 532 nm illumination; inset, infrared imaging temperature distribution map of the device under 532 nm illumination; (d) increased temperature profile of the device under 532 nm laser illumination; (e,f) current voltage ( I – V ) characteristics of the device under 532 and 1177 nm laser irradiation, respectively; (g) photocurrent and temperature variation curves of the device under 532 nm laser illumination. Reproduced with permission from [ 13 ]. Copyright 2020, Optica Pubishing Group. In another novel approach, Zhu et al. designed a flexible, self‐powered composite sensor by integrating CsPbI 3 , rGO, and P(VDF‐TrFE) to create a multifunctional piezo‐phototronic photodetector [ 19 ]. For the fabrication of the device, a viscous slurry of the materials was coated onto a glass substrate using the spin‐coating method and dried at 70°C. After that, the substrate was immersed in water for 2 min to obtain a freestanding CsPbI 3 /rGO/P(VDF‐TrFE) hybrid film. The film was cut into 10 mm × 8 mm rectangles and sandwiched between two PDMS substrates, followed by copper wire electrodes connection for electrical measurements. The device operated by coupling mechanical pressure sensing with light detection, enabled by the piezoelectric and photonic properties of the composite structure. The sensor displayed enhanced thermal, water, and chemical stability. A peak open‐circuit voltage of 12.5 V and a current density of 425 nA were achieved. The piezo‐phototronic effect improved performance by 3.26 times, confirming the efficacy of mechanical modulation in tuning optoelectronic responses. Such hybrid devices hold promise for integration into flexible, multifunctional systems for smart wearable electronics, environmental monitoring, and health diagnostics. Yu et al. introduced a novel p–p Se/rGO heterojunction photodetector utilizing highly crystalline selenium microtubes (Se‐MT) and rGO NSs fabricated via a straightforward spin‐coating technique [ 15 ]. The Se‐MTs, with lengths up to 3 mm, allow facile electrode integration, while the bandgap tuning of rGO (achieved via thermal reduction of GO) provides optimal alignment for charge separation. The Se/rGO photodetector achieved a remarkable responsivity of 168.1 mA/W and a specific detectivity of 1.48 × 10 11 Jones, representing 14× and 135× enhancements, respectively, over pure Se‐MT devices. The device exhibited broadband photoresponse (280–1000 nm) and rapid transient characteristics: 18 μs rise time and 4.76 ms decay time. At 1000 nm, responsivities were 19.5 mA/W (Se/rGO) and 12.1 mA/W (Se/GO), vastly superior to the Se‐MT baseline (~0.05 mA/W). These results underscore the effectiveness of rGO in amplifying broadband responsivity, especially under self‐powered conditions, making the architecture viable for advanced NIR imaging and communication systems. Figure 5a,b shows the change in the responsivity and detectivity of the materials with increasing wavelength. The corresponding band diagrams of the materials are shown in Figure 5c–f . FIGURE 5. Open in a new tab (a) Responsivity and (b) specific detectivity of Se–MT photodetector (PD) measured at a 0.2 V bias, compared with Se/rGO and Se/GO photodetectors operating under zero bias. (c,d) Energy band diagrams of the Se/rGO (c) and Se/GO (d) photodetectors prior to contact. (e,f) Schematic energy band representations of the Se/rGO (e) and Se/GO (f) photodetectors under light illumination, illustrating carrier dynamics. Reproduced with permission from [ 15 ] Copyright 2024, American Chemical Society. In yet another demonstration of rGO's versatility, Padhi et al. (2024) reported a self‐powered UV photodetector combining ferroelectric barium titanate (BaTiO 3 , or BTO) with an rGO nanolayer [ 34 ]. The ferroelectric property of BTO provides intrinsic polarization fields, which effectively drive charge separation in the absence of an external bias. BTO was synthesized via a hydrothermal transformation of a TiO 2 film grown on flexible Ti foil. An rGO layer was spin‐coated to enhance charge mobility and reduce recombination. The device achieved a responsivity of 29.4 A/W, a rise time of ~8.57 ms, and a decay time of ~5.25 ms, with an on/off switching ratio of 28.5. Interestingly, performance was found to be temperature‐dependent and varied with the direction of polarization, in up‐poled mode, photocurrent decreased with rising temperature (from 300–120 nA across 40–80°C). In down‐poled mode, photocurrent remained stable, suggesting a thermally robust polarization state. The hybrid rGO/BTO architecture holds promise for flexible, low‐power UV photodetectors, particularly in wearable and high‐temperature environments. However, consistency in device performance necessitates precise control over rGO coverage and ferroelectric switching characteristics. Collectively, these studies demonstrate that the strategic integration of rGO with perovskites, TMDCs, or ferroelectrics can yield self‐powered photodetectors with exceptional performance across diverse spectral regions from UV to THz. The advances in hybrid device architectures, interfacial engineering, and material processing continue to push the boundaries of zero‐bias photodetection, making rGO‐based hybrids a focal point in the evolution of future sustainable, flexible, and wearable optoelectronics. 2.10. rGO/Silicon Heterojunction‐Based Self‐Powered Photodetectors Silicon (Si), a cornerstone of modern semiconductor technology, remains indispensable across electronic and optoelectronic platforms owing to its well‐established fabrication infrastructure, excellent thermal stability, and favorable charge carrier mobility (~1400 cm 2 V −1 s −1 for electrons). Despite its indirect bandgap of ~1.1 eV, which limits its efficiency in radiative recombination processes, Si exhibits broad spectral absorption (300–1100 nm), making it a key material in applications such as PVs, photodetectors, FETs, and hybrid device systems [ 58 , 59 , 60 , 61 , 62 ]. To overcome limitations associated with its indirect bandgap, silicon is frequently integrated with low‐bandgap or direct‐bandgap materials to boost photocarrier generation and separation. Among these, rGO has emerged as a particularly promising candidate due to its high electrical conductivity, tunable electronic structure, and compatibility with solution processing techniques. This integration yields a synergistic platform wherein silicon serves as a robust broadband absorber while rGO facilitates efficient charge transport and carrier collection. Pioneering work by Periyanagounder et al. demonstrated the potential of graphene/silicon (Gr/Si) van der Waals heterostructures for self‐powered photodetection. Their device exhibited Schottky junction characteristics with a barrier height of 0.76 eV, high responsivity (510 mA/W), fast response time (130 μs), and a substantial on/off switching ratio of 10 5 . The performance attributes are driven by the efficient photocarrier separation at the 2D/3D interface [ 43 ]. Further reviewed by Iqbal et al . in 2023, Gr–Si junctions were recognized for their versatility in high‐speed optoelectronics, ranging from ultrafast photodetectors to integrated plasmonic systems while simultaneously addressing material challenges related to band alignment and carrier recombination [ 63 ]. Building upon these findings, the use of rGO in place of pristine graphene introduces enhanced functional flexibility. Li et al. reported a solution‐processed rGO/n–Si vertical heterojunction photodetector exhibiting strong self‐powered operation. A built‐in electric field at the interface facilitated efficient carrier separation without external bias, yielding high responsivity (1.52 A/W at 600 nm), fast rise (~2 ms) and decay (~3.7 ms) times, and an on/off current ratio of 10 4 [ 18 ]. The photoresponse extended across the UV–NIR range due to the combined absorption capabilities of rGO and Si, while the short carrier transit distance in the vertical geometry enhanced speed. To obtain the vertical geometry, a pair of source–drain Ti/Au electrodes was deposited on the top of Si/SiO 2 layer with the help of the sputtering method. The SiO 2 layer between the electrodes was removed by photoetching and reactive ion etching methods. On top of the exposed n‐Si layer, rGO thin film was drop‐casted and partially contacted with one Ti/Au electrode. The performance and spectral coverage of rGO–Si devices can be further improved by introducing additional semiconducting or organic components. For example, Xiao et al. (2018) engineered a 3D rGO–MoS 2 –pyramid Si heterojunction. This multilayered architecture exploited the broadband absorption of pyramid‐structured Si, defect‐tuned MoS 2 , and high‐conductivity rGO to achieve remarkable detectivity (3.8 × 10 15 Jones), responsivity (21.8 A/W), and an ultra‐broad spectral range (~350 nm to 4.3 μm) with response times as low as 2.8 μs [ 28 ]. Further diversifying the design, Khalili et al . (2021) electrospun a composite of rGO and PVP nanofibers onto p‐type Si, forming a highly rectifying heterojunction. This configuration achieved a rectification ratio of 1121 (±1 V, dark), a strong photosensitivity (~10 10 Jones), and operational stability exceeding 100 days [ 19 ]. The enhanced interfacial area and built‐in electric field facilitated effective charge separation and photocurrent generation under zero bias. In a bio‐inspired approach, Dogan et al . (2022) synthesized a hybrid heterojunction using curcumin (CU) and rGO on n–Si. The optimized CU:rGO ratio (1:1.5) achieved a rectification ratio of ~86,000 and photosensitivity of ~10 5 under intense illumination (~150 mW/cm 2 ), attributed to π–π interactions that inhibited rGO aggregation and improved band alignment at the CU–rGO/n–Si interface [ 20 ]. Yıldırım et al. extended electrospinning‐based photodetector designs in 2023 and 2024 by introducing ZrO 2 –rGO [ 16 ] and poly vinyl alcohol PVA–rGO [ 21 ] nanofiber heterojunctions on n–Si. The ZrO 2 –rGO system leveraged the wide bandgap and transparency of ZrO 2 with rGO's conductivity, achieving a rectification ratio of ~3.7 × 10 4 , responsivity up to 630 mA/W in the UV range, and detectivity of ~10 10 Jones. Besides, the PVA–rGO/n–Si device is a prototypical rGO/Si heterojunction in which self‐powered operation originates from Fermi‐level equilibration and the resulting built‐in electric field across the depletion region. When n–Si and PVA–rGO are brought into contact Figure 6a , electrons flow from n–Si ( χ Si ≈ 4.05 eV, E g ≈ 1.12 eV, EF ≈ 0.2 eV below E c ) into the PVA–rGO layer (Φ rGO ≈ 4.66 eV, effective bandgap ≈ 0.11 eV at O/C ≈ 6.4%) until their Fermi levels align, which produces band bending and an internal electric field that separates photogenerated carriers even at zero external bias. Using the Schottky–Mott picture for an n‐type junction, this corresponds to an electron barrier height φ Bn ≈ Φ rGO − χ Si ≈ 0.61 eV and a complementary hole barrier φ Bp ≈ E g − φ Bn ≈ 0.51 eV, in line with the substantial band bending sketched in the energy‐band diagram, Figure 6b . FIGURE 6. Open in a new tab (a) Schematic and energy‐band diagram of PVA‐RGO/n‐Si device under light exposure (Δ E c , Δ E v , E g and V b are energy difference between conduction bands, difference between valence bands, band gap and energy built‐in voltage, respectively), (b) Schematic representation of current conduction mechanism in heterojunction under light, (c) Variations of barrier height and ideality factor obtained from thermionic emission theory with respect to light intensity, and (d) Variation of the rectification ratio with light intensity for ±2.0 V. Reproduced with permission from [ 21 ] Copyright 2024, IOP publishing. Illumination further modulates this junction: the fitted barrier height decreases from about 0.80 eV in the dark to roughly 0.69 eV at high intensity, while the ideality factor increases from ~2.0 to ~3.5 as shown in Figure 6c signatures of growing trap‐assisted transport and barrier inhomogeneity under strong photogeneration. Consistently, the rectification ratio falls from ~10 6 (dark) to ~10 2 at ~150 mW cm −2 , Figure 6d , indicating that intense photocarrier injection partially flattens the effective barrier and enhances reverse current. Spectral analysis shows that UV photocurrent mainly arises from excitation in the PVA‐rGO layer, whereas the visible‐IR response is associated with interfacial traps and the Si substrate, underlining that band alignment and interfacial states together decide whether the junction operates in a built‐in field dominated, efficient zero‐bias regime or shifts toward recombination‐dominated behavior when traps and barrier lowering prevail. In this favorable alignment regime, the device achieves strong self‐powered performance responsivity of 688 mA W −1 and detectivity of 1.15 × 10 15 Jones at 365 nm, with characteristic response times on the order of 34 ms at zero bias. At higher optical powers, the photoresponse can deviate from linearity and the incremental responsivity may roll off (or saturate) as trap states progressively fill, recombination increases at high carrier density, and the effective junction barrier becomes increasingly screened. These effects constrain the usable linear operating window, which is best captured by the linear dynamic range (LDR) and is critical for imaging and sensing applications. The evolution of rGO‐Si heterostructures for self‐powered photodetectors demonstrates an exciting trajectory from planar Schottky junctions to sophisticated 3D, nanofiber, and hybrid configurations. The consistent trend of leveraging rGO's tunable properties—via chemical reduction, composite formation, and interface engineering—has yielded devices with ultra‐broadband spectral sensitivity, ultrafast response, and high detectivity. Looking forward, key challenges include enhancing reproducibility, minimizing interfacial defects, and achieving scalable, uniform nanomaterial integration. Nonetheless, the unique confluence of silicon's spectral breadth and rGO's electrical agility positions these hybrid architectures as frontrunners in energy‐autonomous optoelectronics for applications spanning wearable sensors, optical communication, and environmental monitoring. 2.11. rGO/Metal Self‐Powered Photodetector Expanding the functional landscape of rGO in optoelectronics, Hu et al. (2021) introduced a novel class of self‐powered photodetectors leveraging the photo‐thermoelectric effect (PTE). Their device architecture employs a freestanding, suspended rGO film asymmetrically contacted with palladium (Pd) and titanium (Ti) electrodes to induce differential carrier doping at the two contact interfaces, as shown in Figure 7 . For the device fabrication, the GO film was placed in an atmosphere composed of 95% argon and 5% hydrogen and annealed at different temperatures, such as 200°C, 400°C, 600°C, 800°C, and 1000°C for 3 h. The heating process produces rGO during the device fabrication [ 22 ]. This asymmetry breaks the spatial carrier symmetry in the rGO layer and enables efficient photo‐generated carrier separation without the need for an externally applied bias voltage. In this configuration, light irradiation across the device induces a localized thermal gradient within the suspended rGO film. Due to rGO's low thermal conductivity and the spatial separation of the metal contacts, incident photons cause uneven heating, leading to a Seebeck voltage, a hallmark of the PTE effect. Hot carriers diffuse from the high‐temperature region toward the cooler electrode, generating a measurable voltage that is inherently energy‐efficient and self‐powered. As shown in Figure 8 , for the photodetectors annealed at 200°C and 400°C, the photovoltages changed from negative to positive, while for the photodetectors annealed at 600°C, 800°C, and 1000°C, the photovoltages were positive. The IV characteristics of the photodetector annealed at 200°C possess a net photocurrent ( I SC ) at zero applied bias along with the open circuit voltage ( V OC ). This property is claimed as the typical PTE signature of the device. The Pd–rGO–Ti photodetector exhibits broadband photoresponse, covering an extraordinary spectral window from UV (365 nm) to terahertz radiation (up to 118.8 mm or 2.52 THz). Such an extensive detection range is largely enabled by rGO's continuous energy band structure and the PTE mechanism, which does not rely on traditional band‐to‐band transitions. Key performance metrics include responsivities ranging from 1.82 to 142.08 mV/W, depending on the spectral region and device geometry, and a detectivity peaking at ~1.58 × 10 7 Jones. In addition to wideband sensitivity, the device offers moderate response times in the range of 100–200 ms, which are adequate for many practical applications such as passive imaging, motion tracking, and IR sensing. Notably, the fabrication process is remarkably straightforward: the rGO films are drop‐cast and thermally reduced under an Ar/H 2 atmosphere, followed by shadow‐mask evaporation of ultra‐thin Pd and Ti contacts. The absence of complex lithography or doping steps makes this approach cost‐effective and scalable. FIGURE 7. Open in a new tab Fabrication process for the PdrGO‐Ti photodetectors. Reproduced with permission from [ 22 ] Copyright 2021, RSC Publishing. FIGURE 8. Open in a new tab Scanning photovoltage measurement of photodetectors annealed at (a) 200°C, (b) 400°C, (c) 600°C, (d) 800°C, and (e) 1000°C, under illumination at 532 nm. (f) I–V curve of the Pd‐rGO‐Ti photodetector, annealed at 200°C, with (red line) and without (black line) laser illumination. Reproduced with permission from [ 22 ] Copyright 2021, RSC Publishing. Importantly, the responsivity and detectivity of the device can be systematically tuned by adjusting key parameters such as the annealing temperature of the rGO film, which influences its Seebeck coefficient and carrier mobility, and by modifying the device geometry, especially the channel length and width. These optimizations allow for flexible design tailored to specific spectral ranges and application demands. Collectively, the Pd–rGO–Ti hybrid photodetector represents a significant advancement in self‐powered, broadband detection technologies. Its reliance on the PTE effect rather than PV mechanisms makes it particularly suitable for ultra‐broadband, low‐light, and low‐energy applications, including next‐generation infrared imaging, terahertz communications, and wearable environmental sensors. The integration of such systems with flexible or suspended substrates further opens avenues for miniaturized and conformal optoelectronic platforms. 2.12. rGO/Nanomaterial Composites‐Based Self‐Powered Photodetectors Yu et al. (2018) introduced a novel self‐powered, ultra‐broadband photodetector based on a vertically aligned CdS nanorod (NRs) array/rGO heterojunction that synergistically utilizes both Schottky‐based carrier separation and the piezo‐phototronic effect [ 23 ]. In this architecture, CdS, a direct bandgap semiconductor (~2.4 eV), not only provides strong UV‐visible photoresponse but also contributes piezoelectric properties essential for piezo‐phototronic enhancement. The narrow bandgap and high carrier mobility of rGO complement CdS, enabling broadband detection spanning 365–1450 nm, all under zero external bias. The device was fabricated by hydrothermally growing CdS NRs on an FTO substrate, over which a spin‐coated GO layer was thermally reduced to rGO. Carbon paste and silver paste served as the top and bottom electrodes, respectively. A Schottky junction forms at the CdS–rGO interface, generating a built‐in electric field that drives efficient carrier separation even in the absence of bias. Impressively, the device achieved a dark‐to‐light current ratio of ~10 5 , a detectivity of ~7.2 × 10 11 Jones, and fast switching characteristics with rise and decay times of 1.3  and 1.7 ms, respectively. Additionally, the application of compressive strain (up to 4%) enhanced the responsivity due to band modulation induced by the piezo‐phototronic effect, increasing the responsivity by ~11%. This work highlights an effective strategy for achieving strain‐tunable, rapid, and broadband photodetection by combining a piezoelectric semiconductor with rGO, offering significant potential for next‐generation adaptive optoelectronic systems. In 2019, Reddeppa et al . developed a solution‐processed hybrid photodetector comprising gold NP‐decorated rGO (Au@rGO) layered over gallium nitride nanorods (GaN NRs), enabling self‐powered detection over both UV and visible spectra. GaN, with its wide bandgap (~3.4 eV), offers excellent chemical and thermal stability, making it ideal for harsh environment applications. However, intrinsic challenges such as spontaneous and piezoelectric polarization often degrade its optoelectronic performance [ 24 ]. To mitigate these issues, the integration of Au@rGO was employed to simultaneously enhance charge transport and introduce LSPR from the embedded Au NPs. The hybrid device demonstrated a dramatic enhancement in zero‐bias responsivity—from a modest 0.00154 A/W for rGO/GaN to 33.40 A/W for Au@rGO/GaN, marking a significant advancement in self‐powered photodetection. Furthermore, response times improved considerably, with rise and decay times reduced to 0.43 s and 0.38 s, respectively. These enhancements were attributed to improved carrier separation at the rGO–GaN interface and plasmon‐induced hot carrier injection from Au NPs, which extended light absorption into the visible region and lowered device resistance. Although long‐term stability remains a concern, this work underscores the effectiveness of plasmonically active, solution‐processed rGO functionalization in transforming wide‐bandgap semiconductors like GaN into broadband, self‐powered photodetectors. Sarkar et al. (2019) presented another high‐performance approach to broadband photodetection using a GaN/rGO:Ag NP heterostructure capped with a transparent Au nanowire electrode [ 25 ]. For device fabrication, n‐doped GaN layer was grown using the molecular beam epitaxy technique on a sapphire(Al 2 O 3 ) substrate. After that, a GO monolayer dispersion solution, along with 8% Ag NPs, was spray‐coated on the GaN/Al 2 O 3 substrate and maintained a thickness of 60 nm. The GO was thenheated at 150°C to produce rGO that also forms a heterojunction with GaN. At the final stage, Au electrode was patterned on the top using the crackle lithography technique. In this device, GaN serves as the UV‐sensitive core material, while the rGO:Ag NP composite layer extends spectral sensitivity into the visible and NIR domains. The Ag NPs not only catalyze the reduction of GO to rGO but also support LSPR, thereby amplifying light absorption and facilitating additional carrier generation. The hybrid device operates under zero bias, with a built‐in electric field across the GaN/rGO interface enabling self‐powered photodetection. It demonstrated notable optoelectronic characteristics, including a UV responsivity of ~0.266 A/W, detectivities on the order of 10 11 Jones, and excellent switching behavior with high on/off current ratios (~10 4 ) and rectification ratios (~10 5 ). The transparent Au nanowire electrode ensured minimal optical loss and efficient carrier extraction, further enhancing the device's performance. Fabricated using scalable techniques such as spray‐coating and crackle lithography, this platform shows great promise for flexible and large‐area optoelectronic integration, though optimization of Ag NP loading and rGO layer thickness remains essential for device uniformity and reproducibility. Zhan et al. demonstrated a self‐powered visible‐light photodetector based on a thermally reduced rGO–ZnO nanohybrid, where high‐temperature processing (700 °C) plays a crucial role in both reducing GO and doping ZnO with carbon atoms [ 52 ]. ZnO, a wide‐bandgap semiconductor (~3.3 eV), typically exhibits strong UV absorption but limited visible‐light sensitivity. However, carbon doping introduced via thermal reduction significantly extends ZnO's absorption into the visible region, enabling it to effectively interact with solar and ambient light. The rGO component facilitates rapid charge transport and forms a heterojunction with ZnO that enables zero‐bias photocurrent generation, as evidenced by I–V measurements showing significant photocurrent under illumination for rGO–ZnO hybrids, but not for rGO alone. This indicates that the synergistic interaction between rGO and ZnO, including efficient interfacial charge transfer and enhanced photo‐generation, is key to the observed performance. The thermal reduction method not only simplifies fabrication but also enables tunability of the device's optical and electrical properties via control of the annealing atmosphere and temperature. This system exemplifies a simple yet effective approach to designing visible‐light active, self‐powered photodetectors, expanding the utility of ZnO through carbon‐based hybridization. Figure 9 schematic indicates the relative alignment of ( E F ), ( E C ), and ( E V ), and proposes that photoexcited electrons generated in ZnO are injected into the highly conductive rGO network, while holes remain in ZnO and drive oxygen adsorption/desorption surface processes. This spatial separation suppresses recombination and yields a net photocurrent without external bias. The study also reports ZnO's band gap (~3.37 eV) and specifies the measurement conditions (400 W Xe lamp; incident power density ~80 mW cm −2 ; sampling period 50 ms). Control carbon‐doped ZnO devices produce only ~2 nA zero‐bias photocurrent and respond slowly (>20 s to reach steady state), indicating that Schottky‐contact effects alone are insufficient; instead, the dominant self‐powered behavior in the hybrid device arises from the rGO–ZnO interface together with rapid carrier transport through rGO, consistent with the much faster response of the rGO–ZnO device (<0.2 s) [ 33 ]. FIGURE 9. Open in a new tab Schematic illustration of charge transfer process involving oxygen‐adsorption upon illumination of (a) undoped ZnO–rGO hybrid, (b) carbon‐doped ZnO–rGO hybrid, the brown lines denote new energy levels generated by carbon doping. Reproduced with permission from [ 33 ] Copyright 2012, Royal Society of Chemistry. In a recent advancement reported by Zhao et al. (2024), a topological insulator–based heterostructure was developed by integrating bismuth telluride (Bi 2 Te 3 ) with rGO to form a Bi 2 Te 3 /rGO heterojunction for broadband, self‐powered PEC photodetection [ 26 ]. Bi 2 Te 3 , a narrow bandgap material (~0.15 eV), is known for its high carrier mobility and strong spin–orbit coupling, making it a promising candidate for optoelectronic and thermoelectric applications. When coupled with rGO, which serves as a high‐conductivity, broadband light‐absorbing medium, the heterojunction benefits from enhanced charge transport and spectral extension into both UV and NIR regions. The device was synthesized via a single‐step hydrothermal process, resulting in an intimate interface between Bi 2 Te 3 NSs and rGO. The built‐in electric field at the heterointerface, arising due to the work function difference between Bi 2 Te 3 and rGO, promotes efficient zero‐bias photogenerated carrier separation, enabling fully self‐driven operation. The photodetector exhibited a broad spectral response ranging from 365 nm (UV) to 850 nm (NIR), a switching ratio ( I ph / I dark ) of ~412, and a responsivity of ~6.07 mA/W under UV illumination. The device also demonstrated a detectivity of 2.41 × 10 10 Jones, indicative of its low‐noise and high‐sensitivity operation. Despite these promising results, the authors noted that device reproducibility and performance consistency are highly dependent on precise control of rGO doping level and hydrothermal synthesis parameters. This study reinforces the feasibility of incorporating topological insulators into rGO‐based heterojunctions, paving the way for next‐generation, low‐power broadband PEC sensors and detectors. In contrast to traditional substrate‐supported architectures, Wen et al. (2019) explored the use of free‐standing rGO as a standalone, substrate‐free photoactive material for fabricating self‐powered photodetectors [ 27 ]. Unlike conventional configurations where the active layer is deposited onto a rigid or flexible substrate, free‐standing rGO eliminates the influence of substrate‐related constraints, such as lattice mismatch, optical losses, and parasitic capacitance, offering a new degree of structural freedom and integration flexibility. The fabrication involved preparing free‐standing GO membranes, which were subsequently annealed under an Ar/H 2 (95%/5%) atmosphere at varying temperatures, 200°C, 400°C, 600°C, 800°C, and 1000 °C to achieve different degrees of reduction. This thermal annealing process played a critical role in tuning the optoelectronic properties of rGO by reducing the concentration of oxygen‐containing functional groups (e.g., hydroxyl, epoxy, carboxyl). These rGO films (10 × 1 mm 2 ) were placed between two pieces of copper conductive adhesives fixed on a hollow Polyformaldehyde substrate separated at a distance of 5 mm. Gold (Au) electrodes were deposited on the rGO films by thermal evaporation using sulfuric acid paper as a shadow mask. These Au electrodes were further connected to conducting wires for electrical measurements. Interestingly, Wen et al. observed a direct correlation between annealing temperature and device responsivity: as the degree of reduction increased, the density of photoreactive functional groups decreased, resulting in progressive reduction of responsivity. Despite this tradeoff, the free‐standing rGO‐based devices displayed ultrafast response times (<50 ms)—which are approximately one to three orders of magnitude faster than those reported for substrate‐supported rGO‐based ultrabroadband photodetectors. This enhancement in response dynamics is attributed to the substrate‐free configuration, which minimizes interfacial defects and dielectric screening effects, thereby promoting faster carrier mobility and extraction. The work by Wen et al. illustrates the viability of free‐standing rGO membranes for high‐speed, self‐powered photodetection and opens up new possibilities for flexible, transparent, and wearable optoelectronics without the need for supporting layers or complex integration steps. A comparison of the self‐powered photodetectors fabricated with different rGO‐based materials is given in Table 2 . TABLE 2. Self‐powered photodetectors fabricated with rGO‐based materials. Sl. no. Material Detectivity Responsivity Response time EQE, % Wavelength range References 1 rGO with a p‐In 2 Se 3 /n‐Si ∼2.39 × 10 12 cm Hz 1/2 W −1 ∼9.5 A W −1 ∼110/110 ms Not reported 900 nm [ 32 ] 2 laser‐scribed rGO LSG/CsPbBr 3 160 × 10 9 Jones 100 mA W −1 18 ms Not reported 405 nm [ 13 ] 3 WS 2 ‐rGO hybrid Not reported 9.3 μA W −1 Not reported Not reported White light [ 14 ] 4 Se/rGO 1.48 × 10 11 Jones 19.5 mA W −1 18 μs/4.76 ms Not reported 368 nm [ 15 ] 5 BTO/rGO Not reported 38.5 A W −1 0.8 s 12 727% 373 nm [ 34 ] 6 graphene/silicon (Gr/Si) Not reported 510 mA W −1 130 µ s Not reported 532 nm [ 43 ] 7 rGO/n‐Si p–n heterojunction Not reported 1.52 A W −1 2 ms Not reported 365–600 nm [ 18 ] 8 rGO and polyvinyl pyrrolidone (PVP) nanofibers >10 10 Jones ~1 mA W −1 Not reported Not reported AM 1.5G illumination [ 19 ] 9 curcumin:rGO/silicon heterojunction 5.5 × 10 8 Jones 1.39 mA W −1 Not reported Not reported AM 1.5 G illumination [ 20 ] 10 ZrO 2 –rGO ~10 10 Jones 630 mA/W Not reported 234% 365 nm [ 16 ] 11 Pd–rGO–Ti 1.06–15.80 × 10 6 cm Hz 1/2 W −1 1.82–142.08  mV W −1 100–200 ms Not reported UV‐THz [ 22 ] 12 CdS nanorod array/rGO ~7.2 × 10 11 Jones 0.58 mA W −1 1.7 ms Not reported 365–1450 nm [ 23 ] 13 rGO/GaN Au@rGO/GaN Not reported 33.40 A W −1 0.43 ms Not reported 382 nm [ 24 ] 14 GaN/rGO 2.62 × 10 11 Jones ~0.266 A W −1 Not reported Not reported 360–980 nm [ 25 ] 15 rGO‐Bi 2 Te 3 heterojunctions 2.406  × 10 10 Jones 6072  µW/A 29  ms Not reported 365–850  nm [ 26 ] 16 rGO 4.23× 10 6 cm Hz 1/2 W −1 87.3  mV W −1 34.4 ms Not reported 375 nm [ 27 ] Open in a new tab 3. Critical Comparison of rGO‐Based Self‐Powered Architectures Tables 1 and 2 show that rGO rarely acts as the primary absorber in self‐powered photodetectors; instead, it most often functions as a tunable contact, an interfacial field former, and a fast lateral transport pathway. The dominant zero bias driving force depends on architecture: PV junction fields in rGO‐Si and related heterojunction stacks, interfacial charge transfer fields in PEC hybrids, and thermodiffusion in PTE devices. Because these mechanisms generate different internal fields and different noise floors, a meaningful comparison must link the device stack to (i) how efficiently photocarriers are separated at zero bias, (ii) how robust and spatially extended the built in field is, and (iii) how strongly dark current and low frequency noise are suppressed under practical operating conditions. Among PV designs, rGO/Si‐based junctions remain the most directly comparable family because the depletion region in Si provides a clear built in field and a well understood route to low dark current. In simple rGO/n Si heterojunctions, rGO primarily behaves as a work function tunable p type contact on n Si, giving reliable self powered operation with strong field driven separation and high on/off ratios when the interface is electronically clean [ 18 ]. Architectures that increase junction area or improve conformity often push detectivity by suppressing leakage paths and stabilizing the barrier, as seen in polymer or nanofiber assisted interfaces such as rGO–PVP and PVA–rGO coatings on n‐Si, where the composite network improves percolation and interfacial uniformity but can introduce trap mediated persistence that must be controlled to preserve response speed [ 19 , 21 ]. More complex Si stacks can further increase charge separation efficiency by combining Si depletion fields with band offset‐assisted extraction in a second layer; for example, rGO‐coupled MoS 2 /pyramid Si designs use light trapping plus improved extraction at the heterointerfaces and can reach very high detectivity with ultrafast dynamics when the junction is well engineered [ 28 ]. In contrast, bulk heterojunction approaches that integrate rGO with layered absorbers can deliver strong responsivity while remaining limited by slower extraction across multiple interfaces; the SnSe 2 ‐rGO/MoS 2 /Si bulk heterojunction illustrates this tradeoff with high responsivity but response times in the 10 −1 s range, consistent with interfacial trapping and recombination acting as practical bottlenecks [ 12 ]. Across the PV category, the recurring limitation is not the availability of a built in field but the electronic quality of the rGO/semiconductor interface: interfacial recombination and barrier inhomogeneity increase dark current, broaden time constants, and reduce detectivity even when responsivity looks impressive [ 18 , 20 , 21 ]. rGO/MO and rGO/wide bandgap semiconductor hybrids broaden the design space because the built in potential can be created through Schottky barriers, p–n junctions, or surface depletion and can be strengthened by plasmonic or piezo phototronic effects. However, this family is more sensitive to microstructure and processing variability, which directly impacts noise and reproducibility. In Ag/rGO‐SnO 2 nanorod devices, rGO improves transport and interfacial extraction while Ag enhances local fields, leading to large improvements in on/off ratio and photocurrent, but the response remains in the sub second regime because surface states and interfacial trapping dominate the kinetics [ 17 ]. CdS nanorod array/rGO junctions can achieve very high light to dark ratios with ms scale response, indicating strong field separation with comparatively low leakage, yet they still require careful interface control to prevent recombination losses that would otherwise erase the detectivity advantage [ 23 ]. GaN‐based systems show an additional tradeoff: when rGO is used as a transparent contact and extraction layer, responsivity and detectivity can be high, but trap rich interfaces may broaden the response and complicate the noise floor, especially when plasmonic NPs are introduced to enhance absorption [ 24 , 25 ]. A common bottleneck in this architecture class is that the built in field is often confined near nanostructured surfaces, so performance depends on whether photocarriers are generated inside the field region and extracted before recombination; this makes the devices highly sensitive to morphology, defect density, and contact resistance, which then feeds into dark current and 1/f noise [ 17 , 23 , 25 ]. Perovskite‐coupled and perovskite‐derived architectures not only highlight the strongest responsivity potential but also expose the sharpest stability and complexity constraints. When rGO is chemically integrated as a transport and contact layer, very large gain like responsivity can be reported, but the comparison across platforms must account for whether the device remains truly self‐powered in a robust manner or whether bias‐assisted transport and trap filling contribute to the apparent gain [ 29 ]. Laser‐scribed graphene‐based PTE devices with perovskite coupling represent the opposite end of the spectrum: the architecture can be fabrication friendly, can cover very broad spectral ranges, and can achieve low noise equivalent power, but the responsivity is typically modest compared with the highest gain PV stacks, reflecting the fundamental limitation that PTE signals depend on maintaining temperature gradients rather than maximizing optical absorption in a depletion region [ 13 ]. In practice, perovskite‐based routes therefore trade fabrication and materials stability against responsivity, and they demand stronger encapsulation and interface engineering to keep recombination and drift noise under control over time [ 29 ]. TMD and chalcogenide hybrids emphasize interfacial field engineering and charge transfer rather than classical depletion regions. In PEC‐type configurations such as WS 2 /rGO, rGO mainly provides a conductive extraction pathway and suppresses series resistance, but the effective built in field is tied to the semiconductor/electrolyte interface and can be weaker or more environment dependent than in solid state PV junctions, which is why responsivity is often modest even when stability metrics are encouraging [ 14 ]. By contrast, solid‐state p–p or type II heterojunction designs using Se‐based structures with rGO can create strong internal band offsets that support fast rise dynamics and respectable detectivity while still remaining sensitive to recombination at the rGO junction and to contact induced barrier variations [ 15 ]. These systems make clear that limited absorption in ultrathin rGO is not the core limitation; the real limiter is whether the partner absorber generates carriers close enough to a strong internal field and whether rGO provides a low resistance escape route without introducing a dense trap manifold that slows extraction [ 14 , 15 ]. Finally, PTE architectures provide an important noise and bandwidth perspective because they can be intrinsically self‐powered without relying on depletion widths, but they must manage a different set of constraints. Pd‐rGO‐Ti and free standing rGO film devices demonstrate ultrabroadband response that is consistent with thermoelectric conversion, and they often report performance in terms of voltage responsivity and NEP rather than the current based metrics used for PV stacks [ 22 , 27 ]. Their practical advantage is low leakage and potentially good noise behavior when contact asymmetry is well controlled, while their practical disadvantage is that responsivity is ultimately limited by achievable temperature gradients and thermal management, making device geometry and packaging as important as the electronic interface [ 22 , 27 ]. Taken together, the tables support three general conclusions. First, the strongest built in fields and the most predictable self‐powered operation typically come from PV junctions on Si, but only when interfacial recombination is aggressively suppressed and barrier homogeneity is preserved [ 18 , 21 , 28 ]. Second, the highest reported responsivities are often associated with more complex stacks where trap‐assisted gain and interfacial states can inflate responsivity at the expense of speed, stability, and noise, so tradeoffs must be evaluated using detectivity, NEP, dark current, and response time together rather than responsivity alone [ 12 , 20 , 29 ]. Third, architectures that rely on ultrathin rGO layers must compensate for limited optical absorption by pairing rGO with a strong absorber and by ensuring that carrier generation occurs within the reach of a robust internal field; otherwise, interfacial recombination dominates and the self‐powered advantage collapses into low signal and high variability [ 14 , 15 , 17 , 23 ]. 4. Future Prospects and Outlook rGO's complex and tunable electronic structure enables efficient light absorption from UV to THz, making it ideal for broadband and ultra‐broadband photodetection. By engineering heterostructures (e.g., rGO with CdS, GaN, Bi 2 Te 3 ), the spectral range can be extended and responsivity can be enhanced. The future lies in combining rGO with low‐dimensional materials (e.g., quantum dots, perovskites, TMDs) to push detection limits into the deep UV or far‐IR regions. In parallel, designing multijunction architectures to exploit multiple absorption edges can achieve high quantum efficiency. Moreover, free‐standing rGO, thin‐film architectures, and solution‐based fabrication offer unique possibilities for flexible, bendable, and wearable optoelectronics. The integration with soft substrates (e.g., PDMS, PET) and stretchable electrodes can lead to self‐powered photodetectors embedded in e‐skins, smart textiles, or biomedical devices for continuous environmental or physiological monitoring. Conformal detectors for irregular surfaces, enabling applications in robotics or implantable sensors. The ability of rGO heterostructures to operate without external power makes them ideal for autonomous sensing platforms. Future developments could integrate photodetection with energy harvesting modules (e.g., piezoelectric, triboelectric, thermoelectric) for all‐in‐one sensor‐energy systems. Additionally, Internet of Things applications require low‐power, long‐lifetime sensors that are essential. Due to the fast‐switching speed and broad spectral response, rGO‐based detectors have potential in neuromorphic computing, where photoresponse characteristics can mimic synaptic functions. This opens up pathways for photonic logic gates, artificial retina systems, optoelectronic memory, and learning devices Despite the future possibilities, still challenges in designing rGO‐based self‐powered photodetectors are present. For instance, related to the material heterogeneity and reproducibility, rGO derived from GO reduction is highly dependent on processing conditions (e.g., temperature, time, reducing agents), resulting in variability in electrical and optical properties. The challenges lie are the lack of uniformity and control over oxygen functional groups, leading to batch‐to‐batch inconsistency and poor reproducibility. A possible solution will be to adopt standardized synthesis protocols (e.g., controlled thermal or chemical reduction) and characterization benchmarks (e.g., XPS, Raman) to ensure consistent rGO quality. Alternatively, doping and passivation strategies may be used to tailor rGO properties reproducibly. Effective self‐powered operation relies on the built‐in electric field at rGO semiconductor junctions. However, poor interface quality often leads to trap states, recombination losses, and leakage current. The challenge comes from the imperfect contact at the rGO/semiconductor interface which degrades charge separation and collection. A possible solution would be to employ surface functionalization, interfacial layers, or graded doping to improve band alignment and minimize trap‐assisted recombination. Additionally, van der Waals heterojunctions with atomically clean interfaces (e.g., rGO–2D materials) offer improved control. Furthermore, rGO‐based devices often suffer from performance degradation over time, especially under ambient conditions involving humidity, oxygen, and thermal cycling. The challenge comes from the oxidation, delamination, or deterioration of rGO and partner materials, which reduces device reliability. Therefore, the use of encapsulation layers (e.g., hBN, polymer overcoats) and chemically robust composites can be a possible solution. Introducing inert dopants or forming covalent interfaces can further enhance environmental stability. Highly responsive rGO detectors sometimes suffer from slow response times, especially when charge traps or slow transport layers are involved. The challenge lies in the tradeoff between high responsivity and fast switching. Therefore, optimizing channel length, contact geometry, and carrier mobility through dimensional control and hybridization with high‐mobility materials would be a possible solution to mitigate the existing challenges. Utilizing plasmonic nanostructures (e.g., Au or Ag NPs) can enhance local fields and speed up response. Finally, despite the promising lab‐scale results, large‐area, uniform integration of rGO with silicon‐based platforms remains underdeveloped. The challenge is the incompatibility of some wet chemical processes with CMOS or photolithography workflows. Focus on solution‐processed or inkjet‐printed rGO films compatible with low‐temperature processing, and explore transfer printing techniques to integrate with existing circuits, will be a feasible solution. rGO‐based self‐powered photodetectors represent a compelling direction for next‐generation optoelectronic devices, thanks to their tunable optoelectronic properties, broadband absorption, and compatibility with various nanomaterials. Moving forward, interdisciplinary approaches involving materials science, device physics, chemical engineering, and microfabrication will be essential to overcome current limitations. Key strategies include controlled synthesis and doping of rGO for consistency, advanced interface and band engineering, multifunctional integration with energy harvesting technologies, and the development of flexible, scalable platforms. With these advancements, rGO‐based photodetectors are poised to play a crucial role in low‐power sensing, environmental monitoring, wearable electronics, and even neuromorphic and quantum photonics in the future. 5. Conclusion Self‐powered photodetectors represent a transformative class of optoelectronic devices that can convert incident light into electrical signals under zero‐bias conditions or without the need for an externally applied power source. This self‐driven operation fundamentally relies on the intrinsic photophysical properties of the active materials and the device architecture, which together govern the efficiency of photocarrier generation, separation, and collection. In this context, GO and its reduced form, rGO, have emerged as promising candidates for the development of next‐generation self‐powered photodetectors. Particularly, rGO offers a versatile material platform due to its tunable electronic properties, which stem from the variable degree of reduction, functional group density, and lateral dimensions. The ability to modulate the bandgap of rGO through controlled synthesis and chemical modification is a significant advantage, allowing it to respond to different regions of the electromagnetic spectrum. Moreover, rGO readily forms hybrid structures with semiconductors, enhancing interfacial charge transfer and enabling broadband photodetection. A central concept in self‐powered device design is bandgap engineering, which involves selecting or designing semiconductors with tailored bandgaps. This enables the devices to be sensitized to specific wavelengths, thereby generating photocurrent in the absence of an external bias. In such architectures, rGO typically serves as a high‐mobility charge transport layer or an electron/hole acceptor, facilitating the separation and collection of photoinduced carriers. When integrated with materials exhibiting spontaneous polarization (e.g., ferroelectrics or certain piezoelectric semiconductors), the built‐in electric field at the rGO–semiconductor interface can further drive carrier dynamics in a self‐sustaining manner. Despite these advantages, the number of studies exploring rGO and rGO‐based composites for self‐powered photodetection remains limited when compared to conventional photodetectors that operate under applied bias. A thorough review of the current literature reveals a critical observation: no experimental studies have yet conclusively demonstrated that pristine rGO alone can function as a self‐powered photodetector, capable of generating a measurable photocurrent at zero bias without the assistance of additional semiconductor components or external fields. Instead, most self‐powered architectures rely on junctions—often involving self‐polarized or strongly asymmetric materials—to establish the internal electric fields necessary for charge separation. Another notable limitation in current self‐powered photodetector designs is the relatively low photocurrent output under zero‐bias conditions, which directly impacts device responsivity, detectivity, and overall performance. This challenge is particularly prominent in rGO‐based systems, where the efficient transport of photocarriers can be hindered by residual oxygen functionalities, interfacial defects, or suboptimal band alignment. Therefore, the field remains ripe for innovation. Future research should focus on developing novel rGO‐based composites with enhanced charge separation and transport properties, exploring synergistic combinations with ferroelectric, piezoelectric, or PV materials to establish stronger built‐in fields, engineering device architectures (e.g., vertical heterostructures, asymmetric junctions) that promote directional carrier flow, and employing advanced fabrication techniques, such as laser reduction, plasma treatment, or interfacial functionalization, to tailor material interfaces at the nanoscale. In summary, while rGO holds great potential as a functional component in self‐powered photodetectors, realizing high‐performance devices will require both material innovation and device engineering. Continued interdisciplinary efforts are essential to unlock the full capabilities of rGO in enabling efficient, zero‐bias, broadband photodetection systems for next‐generation optoelectronic applications. Conflicts of Interest The authors declare no conflicts of interest. Acknowledgments Bitap Raj Thakuria acknowledges the Department of Chemistry, Gauhati University, Guwahati. Bedanta Gogoi acknowledges the support of the Department of Science and Technology, Government of India; the Department of Chemistry, Gauhati University, Guwahati; and the Department of Chemical Sciences, Tezpur University. Contributor Information Bedanta Gogoi, Email: [email protected]. Amreen Ara Hussain, Email: [email protected]. References 1. Liu Y., Shivananju B. N., Wang Y., et al., “Highly Efficient and Air‐Stable Infrared Photodetector Based on 2D Layered Graphene–Black Phosphorus Heterostructure,” ACS Applied Materials & Interfaces 9 (2017): 36137–36145. [ DOI ] [ PubMed ] [ Google Scholar ] 2. 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