Conformational entropy tuning in nonfused-ring electron acceptors for low-cost and record-efficiency organic solar cells.

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Learn more: PMC Disclaimer | PMC Copyright Notice Natl Sci Rev . 2026 Mar 19;13(9):nwag177. doi: 10.1093/nsr/nwag177 Conformational entropy tuning in nonfused-ring electron acceptors for low-cost and record-efficiency organic solar cells Xiaobin Gu 1, 4 , Rui Zeng 2, 4 , Fei Han 3 , Jing Li 4 , Senke Tan 5 , Jikai Lv 6 , Na Yu 7 , Lixuan Kan 8 , Hao Li 9 , Yuqi Hou 10 , Yunhao Cai 11 , Zhixiang Wei 12 , Zheng Tang 13 , Lianrui Hu 14 , Feng Liu 15, ✉ , Xin Zhang 16, ✉ , Hui Huang 17, 18, 19, ✉ Author information Article notes Copyright and License information 1 College of Materials Science and Opto-Electronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 101408, China 2 School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, China 3 School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, China 4 Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, Shanghai Frontiers Science Center of Molecule Intelligent Syntheses, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200241, China 5 School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, China 6 College of Materials Science and Opto-Electronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 101408, China 7 Center for Advanced Low-Dimension Materials, State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, China 8 School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, China 9 School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, China 10 College of Materials Science and Opto-Electronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 101408, China 11 College of Materials Science and Opto-Electronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 101408, China 12 Center for Excellence in Nanoscience (CAS), Key Laboratory of Nanosystem and Hierarchical Fabrication (CAS), National Center for Nanoscience and Technology, Beijing 100190, China 13 Center for Advanced Low-Dimension Materials, State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, China 14 Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, Shanghai Frontiers Science Center of Molecule Intelligent Syntheses, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200241, China 15 School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, China 16 College of Materials Science and Opto-Electronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 101408, China 17 College of Materials Science and Opto-Electronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 101408, China 18 School of Chemical Engineering and Technology, State Key Laboratory of Chemical Engineering and Low-Carbon Technology, Tianjin University, Tianjin 300072, China 19 The International Joint Institute of Tianjin University, Fuzhou 350205, China ✉ Corresponding author. E-mail: huihuang@ucas.ac.cn ✉ Corresponding author. E-mail: zhangxin2019@ucas.ac.cn ✉ Corresponding author. E-mail: fengliu82@sjtu.edu.cn 4 Xiaobin Gu and Rui Zeng Equally contributed to this work. Roles Xiaobin Gu : Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing - original draft Rui Zeng : Data curation, Formal analysis, Investigation, Methodology Fei Han : Formal analysis, Investigation, Methodology Jing Li : Formal analysis, Investigation, Software Senke Tan : Formal analysis, Investigation, Methodology Jikai Lv : Investigation, Resources, Software Na Yu : Investigation, Methodology Lixuan Kan : Formal analysis, Investigation Hao Li : Investigation, Methodology Yuqi Hou : Investigation, Methodology Yunhao Cai : Investigation, Supervision Zhixiang Wei : Investigation, Software Zheng Tang : Resources, Software Lianrui Hu : Investigation, Methodology, Software Feng Liu : Formal analysis, Investigation, Methodology, Supervision Xin Zhang : Funding acquisition, Investigation, Supervision, Writing - original draft, Writing - review & editing Hui Huang : Funding acquisition, Resources, Supervision, Writing - review & editing Received 2025 Oct 21; Revised 2026 Feb 2; Accepted 2026 Mar 17; Collection date 2026 May. © The Author(s) 2026. Published by Oxford University Press on behalf of China Science Publishing & Media Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( https://creativecommons.org/licenses/by/4.0/ ), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. PMC Copyright notice PMCID: PMC13221954  PMID: 42220450 ABSTRACT The commercial viability of organic solar cells (OSCs) is hindered by the trade-off between cost and performance. In particular, low-cost non-fused-ring electron acceptors (NFREAs) suffer from conformational disorder, limiting their photovoltaic performance. Herein, we strategically regulate conformational entropy ( S conf. ) of NFREAs through the rational combination of intramolecular noncovalent interactions (INIs). The optimal candidate 3TT-SeS, identified through comprehensive density functional theory calculations, exhibits balanced Se···N and S···O INIs and demonstrates a significant reduction in S conf . This strategy enables an exclusive single stable conformation and highly ordered molecular packing, thereby facilitating efficient charge transport. Consequently, the 3TT-SeS-based OSC achieved an outstanding power conversion efficiency of 19.26% (certified at 18.75%), setting a new benchmark for NFREA-based systems to date. More importantly, 3TT-SeS-based device demonstrates exceptional economic potential with an extremely low power generation cost of 0.77$ kW −1 , much lower than several high-performance FREA-based systems. Our work demonstrates a low- S conf. design of NFREAs for cost-effective and high-performance organic photovoltaics. Keywords: organic solar cells, highly cost-effective, non-fused-ring electron acceptors, conformational entropy, intramolecular noncovalent interactions Forget the ‘cost vs. efficiency’ trade-off: our low-cost organic photovoltaic materials broke the 19% efficiency barrier, setting a new benchmark for affordable clean energy. INTRODUCTION Organic solar cells (OSCs) have demonstrated great potential for multi-scenario applications due to their unique advantages, including solution processability, mechanical flexibility, and tunable transparency [ 1–3 ]. Remarkable progress in both material design and device engineering [ 4–6 ], particularly through the groundbreaking invention of fused-ring electron acceptors (FREAs) [ 7–9 ], has propelled the power conversion efficiencies (PCEs) of OSCs beyond 20% [ 10–16 ]. Despite these achievements, the field faces a long-standing cost-efficiency paradox that substantially hinders large-scale commercialization due to the complex molecular structures and costly synthetic processes required for FREAs [ 17 , 18 ]. In response, non-fused-ring electron acceptors (NFREAs) have emerged as promising candidates for low-cost OSCs. NFREAs feature simple-structured and σ -bond-connected conjugated backbones that enable facile and scalable synthesis [ 19–28 ], yet their structural flexibility presents two fundamental challenges: (i) conformational distortion (large torsion angles) and (ii) conformational disorder (coexistence of several conformers) (Fig. 1a and Fig. S1 , Table S1 ). Current research has predominantly addressed the first challenge through planarization-oriented molecular engineering, achieving improved backbone coplanarity [ 29–34 ]. Nevertheless, the equally critical issue of conformational disorder has been largely neglected, highlighting the urgent need for innovative design paradigm in developing conformer-free NFREAs. Figure 1. Open in a new tab Comprehensive DFT calculations. (a) Fundamental challenges posed by rotatable σ -bonds. (b) Design strategy for model NFREAs. (c) Flowchart of DFT calculation procedures. (d) Geometric parameters and formula for calculating S INI values: r w is the sum of van der Waals radii of two involved atoms; Δ d is defined as r w – d . (e) S INI values under different chalcogen substitutions (Each data point represents the computed S INI value for a specific INI site (X, Y = O, S, or Se) within a candidate NFREA. Refer to Table S3 for detailed values). (f and g) PES scan curves. (h) Equilibrium constants between stable and metastable states. (i) Four-quadrant diagram of two K values and MOC index. Conformational entropy ( S conf. ), a fundamental thermodynamic parameter quantifying the extent of conformational disorder within molecular systems, holds a pivotal position in both chemistry and biology [ 35–38 ]. Essentially, the Boltzmann entropy formula ( S conf. = k B ln W , where W denotes the number of accessible conformations [ 39 ]) establishes that reducing S conf. directly correlates with decreased conformational disorder. This principle finds remarkable parallels between biological macromolecular folding and the aggregated structural ordering of organic semiconductors [ 40 , 41 ]. During polypeptide-to-protein folding, the significant reduction in S conf. is essential for forming structurally defined assemblies with biological functionality [ 42–44 ]. Analogously, suppressing conformational disorder in organic semiconductors is crucial for achieving the highly ordered molecular packing and efficient charge transport required for high-performance organic optoelectronic devices [ 45–47 ]. Therefore, establishing a rational design paradigm to reduce S conf. could unlock the full potential of NFREA in cost-effective OSC applications. In this contribution, we proposed a low- S conf. design of NFREAs and systematically investigated its influence on molecular self-assembly and photovoltaic performance. Through comprehensive density functional theory (DFT) calculations on NFREAs with varied intramolecular noncovalent interactions (INIs), we identified molecules exhibiting both low- S conf. and cost-effectiveness. Subsequently, we successfully synthesized the top-two candidates (3TT-SeS and 3TT-SSe), and conducted comprehensive theoretical and experimental analyses. The results revealed that 3TT-SeS, featuring balanced INIs, demonstrated a significant S conf. reduction, exhibiting an exclusive single conformation, highly ordered self-assembled structure, and favorable blend-film morphology. Thus, 3TT-SeS based OSCs achieved a record-high value of 19.26% (certified at 18.75%) for low-cost NFREA-based ones. Impressively, the 3TT-SeS based devices achieved a substantially lower power generation cost (0.77$ kW −1 ) than the state-of-the-art FREA-based ones, such as D18-Cl: BTP-C3F (3.69$ kW −1 at 20.80% PCE). RESULTS AND DISCUSSION Comprehensive DFT calculations Developing NFREAs with low- S conf. is challenging, primarily due to the intricate rotational dynamics associated with multiple σ -bonds. To overcome this, we performed comprehensive DFT calculations based on model molecules, which offer a promising alternative to empirical trial-and-error methods for guiding the synthetic prioritization of novel materials [ 48 , 49 ]. Our strategy involves the incorporation of chalcogens (oxygen, sulfur, or selenium) into the design of model NFREAs, denoted as 3TT-XY (X, Y=O, S, or Se) ( Fig. S2 ). This design enables the construction of various possible INIs, including S···N, Se···N, S···O, and Se···O (Fig. 1b ). This screening process encompasses five key steps (Fig. 1c ): (i) optimizing molecular geometry using DFT calculations; (ii) extracting geometric parameters to quantify the INI strength using an established descriptor ( S ) [ 50 ]; (iii) analyzing the rotational dynamics of individual σ -bonds; (iv) assessing synergistic effects among multiple σ -bonds; and (v) calculating synthesis costs to ensure alignment with the low-cost design goal. As illustrated in Fig. S3 , the optimized molecular geometries of all model NFREAs exhibit a relatively planar backbone. The extracted geometric parameters are summarized in Table S2 . Notably, the torsion angles θ 1 (∼18°) and θ 2 (∼0°) are consistent with statistical data obtained from reported crystals. The intramolecular distances ( d ) observed in these models indicate chalcogen-driven INIs, with atom pairs (O···S: 2.86 Å, S···N: 3.12 Å, and Se···N: 2.93 Å in 3TT-XS; O···O: 2.70 Å, S···O: 2.71 Å, and Se···O: 2.63 Å in 3TT-SY) exhibiting substantial contraction compared to their van der Waals radii sums ( r w ) ( Table S3 ). To quantify the strength of these INIs, the S INI values are calculated and found to range between 0.178 and 0.188, 0.052–0.069, 0.525–0.601, 0.0096–0.0097, 0.513–0.537, and 1.287–1.385, respectively (Fig. 1d–e , Table S3 ). Note that a larger S INI value implies a stronger INI, which is expected to stabilize the molecular conformation [ 50 ]. Due to the minimal fluctuation in each S INI value, 3TT-XS and 3TT-SY were selected as representatives to investigate the rotational dynamics of single bonds σ 1 and σ 2 , respectively, through relaxed potential energy surface (PES) scans ( Fig. S4 and Fig. 1f–g ). For σ 1 in the 3TT-XS series, when X is oxygen, the stable syn -conformation has a torsion angle θ 1 of 180°. In contrast, when X is sulfur or selenium, the preferred anti -conformation exhibits a torsion angle θ 1 of 30° and 0°. It is worth noting that the steepness of the potential energy curves can be quantified by their first derivative, with steeper curves indicating a reduced probability of the coexistence of anti- / anti - or syn- / syn - conformers [ 51 ]. As shown in Fig. S5 , the derivative values at 10° near the energy minima of the PES curves follow the trends of 3TT-SeS > 3TT-SS > 3TT-OS for σ 1 and 3TT-SSe > 3TT-SS > 3TT-SO for σ 2 , respectively. This result indicates that stronger INIs (corresponding to larger S INI values) not only facilitate planar conformation but also effectively suppress conformer coexistence. In addition, the energy differences (Δ E s-ms ) between the stable and metastable states are 8.442, 0.415, and 14.245 kJ mol −1 for 3TT-OS, 3TT-SS, and 3TT-SeS, respectively. For σ 2 in the 3TT-SY series (with chalcogen substitution at the Y position), the torsion angle θ 2 is consistently located at 0° for all candidates. The Δ E s-ms are 3.613, 18.858, and 34.440 kJ mol −1 for 3TT-SO, 3TT-SS, and 3TT-SSe, respectively. Using the equation K = exp(−Δ E s-ms / RT ) [ 52 ], the equilibrium constant ( K ) for these two anti- / syn - conformers can be calculated to determine their relative populations under thermodynamic equilibrium, thereby reflecting their stability preferences. A K value below 0.01 suggests that the dominant conformer ( R dominant conf. ) accounts for >99% of the population, thereby implying low S conf. As shown in Fig. 1h and Table S4 , the K values of 3TT-OS, 3TT-SS, and 3TT-SeS, based on σ 1 rotation, are 0.0332, 0.8459, and 0.0032, respectively, while those of 3TT-SO, 3TT-SS, and 3TT-SSe, based on σ 2 rotation, are 0.2328, 0.0005, and 9 × 10 −7 , respectively. These findings demonstrate that Se···N, S···O, and Se···O INIs play a crucial role in reducing S conf. , achieving conformational control comparable to pseudo-ladder [ 53 , 54 ] and hydrogen-bonded systems [ 55 , 56 ]. Importantly, INIs introduce superior design flexibility and synergistic effects, allowing simultaneous regulation of electronic structures [ 57 ]. The structural characteristics of multiple rotatable σ -bonds in NFREA systems necessitate a systematic assessment of the possibility of coexisting conformations. In NFREAs possessing σ 1 and σ 2 bonds, a K -value-mediated four-quadrant plot analysis identifies (0.01, 0.01) as the critical threshold dividing isomer-free and isomer-prone regions (Fig. 1i ). This reveals that only candidates with dual K -values below 0.01, exemplified by 3TT-SeS and 3TT-SeSe, exhibit negligible isomer coexistence and low S conf . Cost-effectiveness emerges as an equally crucial consideration in the practical development of NFREAs. A material-only cost (MOC) analysis demonstrates that the key building block 3R-SeS exhibits significantly lower synthesis costs compared to 3R-SeSe ( Fig. S6 and Table S5 ) [ 58 ], thereby establishing 3TT-SeS as the optimal candidate, combining low cost with low S conf. among all model NFREAs. These results demonstrate both the significant potential of selenium-containing NFREAs in advancing OSC technology and the urgent requirement for environmentally friendly and efficient synthetic strategies for these materials. Characterization of low- S conf. NFREAs Following the DFT calculation results, we synthesized the optimal candidate, 3TT-SeS, and the secondary candidate, 3TT-SSe, as a comparative reference. The chemical structures and synthesis details for both NFREAs are depicted in Figs 2a and S7 . Both acceptors demonstrated good thermal stability, with thermal decomposition temperatures (corresponding to 5% weight loss) exceeding 300°C ( Fig. S8 ). To gain a deep understanding of INIs within the acceptors, natural bond orbital (NBO) analysis was conducted. The results revealed significant orbital overlaps: (i) between the n-orbital of nitrogen lone pair and σ *(S−C or Se−C) anti-bonding orbitals, and (ii) between the 2p electron lone pair on the carbonyl oxygen atom and σ *(S−C or Se−C) orbitals ( Fig. S9 ). The orbital interaction energies ( E (2) ) that exhibit a negative correlation with INI strength ( S INI values) were calculated as −0.83/−3.24 kcal mol −1 for n (N)→ σ *(S−C)/ σ *(Se−C) and −6.43/−1.37 kcal mol −1 for n (O)→ σ *(Se−C)/ σ *(S−C), respectively. These results not only confirm the existence of INIs within both NFREAs, but also reveal a rational combination: the transformation from weak S···N and strong Se···O INIs in 3TT-SSe into balanced Se···N and S···O INIs in 3TT-SeS, which is expected to restrict the σ 1 -bond rotation, thereby leading to the effective elimination of rotational freedom in 3TT-SeS. Figure 2. Open in a new tab Characterizations of low- S conf. NFREAs. (a) Chemical structures. (b and c) Conformer population of 3TT-SSe (b) and 3TT-SeS (c) as calculated through quantum chemistry. (d) Single-crystal structures. (e) Intermolecular stacking modes. (f) Crystal packing diagrams. To investigate the impact of rational INI combinations on S conf. of NFREAs, we employed a conformational search program to generate 2000 conformations through σ -bond rotation simulations in the conjugated backbone [ 59 ]. The top five low-energy conformers (Confs. 1–5) were selected, and their population ratios were calculated using the Boltzmann distribution in relative Gibbs free energies. As shown in Fig. 2b–c , Fig. S10 , and Table S6 , 3TT-SSe exhibited three dominant conformers with comparable populations (33.633%, 33.126%, and 31.340%), while 3TT-SeS demonstrated an almost exclusive preference for a single conformation (99.750%), thus resulting in a significantly reduced S conf. of 0.162 J mol −1 K −1 , much smaller than that of 3TT-SSe (9.849 J mol −1 K −1 ). This stark contrast in conformational diversity highlights the accuracy of computer-aided screening in achieving conformer-free and low- S conf. NFREAs. To explore the influence of reduced S conf. on molecular conformation and aggregation structure, needle-shaped crystals of 3TT-SSe and 3TT-SeS were grown using the solvent diffusion method for single-crystal X-ray diffraction analysis. Crystallographic data revealed that 3TT-SSe crystallized in the triclinic P -1 space group, while 3TT-SeS belonged to the monoclinic P 2 1 /c space group ( Tables S7 and S8 ). As illustrated in Figs 2d , S11 , and Table S9 , the 3TT-SSe unit cell existed as a mixture of two distinct conformers (1:1 ratio), characterized by the torsion angles θ 1 = 14.93° and 19.22° for Confs. 1 and 2, respectively. The intramolecular distances ( d intra ) for S···N (2.92 Å) and Se···O (2.70 Å) are notably shorter than the sums of relevant van der Waals radii ( r w, S···N = 3.35 Å and r w, Se···O = 3.40 Å), supporting the existence of S···N and Se···O INIs. Notably, the coexistence of dual conformers in ‌3TT-SSe mainly arises from the insufficient restriction of σ 1 -bond rotation, attributed to the relatively weak S···N INIs with small S INI values (0.254 for Conf. 1 and 0.120 for Conf. 2). In contrast, 3TT-SeS displayed a monoconformational behavior around the σ 1 -bond with near-planar conjugated backbone (θ 1 /θ 2 = 0.02°/0.10°). This conformation is stabilized by moderate-strength Se···N ( d intra, Se···N = 3.02 Å) and S···O ( d intra, S···O = 2.69 Å) INIs, as confirmed by the higher S INI values (0.358 for Se···N; 0.563 for S···O). These results demonstrate that the INI combination strategy effectively restricts the rotation of multiple σ -bonds, achieving an exclusive single conformation in 3TT-SeS. Comparative analysis of packing architectures revealed distinct molecular assembly behaviors (Fig. 2e and f ). The 3TT-SSe crystal possessed a dual-mode assembly, featuring intermolecular π···π interactions ( d π···π = 3.20 Å) in Mode 1 and dual intermolecular hydrogen bonds ( d inter, C≡N···H = 3.29 Å and d inter, F···H = 3.23 Å) in Mode 2. Notably, mediated by intermolecular S···F and Se···F interactions ( d inter, S···F = 3.69 Å and d inter, Se···F = 3.69 Å), 3TT-SeS crystallized in a slipped-stack arrangement, where each molecule was surrounded by four neighbors. The slightly increased intermolecular distances observed in 3TT-SeS may be attributed to the larger atomic radius of selenium atoms [ 60 ]. Therefore, the denser packing mode resulted in a significant increase in the packing coefficient ( C packing ) from 56.1% for 3TT-SSe to 64.7% for 3TT-SeS, which facilitates efficient charge transport (Fig. 2f ) [ 61 ]. The above findings collectively demonstrate that the rational combination of INIs may not only reduce the S conf. but also promote the formation of highly ordered self-assembled structures. Photophysical properties and stacking behavior The photophysical properties of 3TT-SSe and 3TT-SeS were systematically probed through a combination of spectroscopic techniques and theoretical calculations. In dilute chloroform solutions, 3TT-SSe exhibited maximum absorption and emission peaks at 745 and 849 nm, respectively. In contrast, 3TT-SeS displayed blue-shifted absorption (732 nm) and emission (830 nm) peaks (Fig. 3a and Table S10 ). Upon transitioning to the solid state, both acceptors exhibited red-shifted absorption/emission maxima: 3TT-SSe at 807/908 nm and 3TT-SeS at 781/872 nm (Fig. 3b and Fig. S12 ). In addition, the 3TT-SeS thin film demonstrated a higher molar extinction coefficient (1.36 × 10 5 cm −1 ) compared to 3TT-SSe (1.21 × 10 5 cm −1 ), suggesting a tighter packing for 3TT-SeS [ 62 ], consistent with single-crystal X-ray diffraction results. Combining absorption and emission properties, we found that the Stokes-shifts (Δ v ) for 3TT-SeS in solution and film (1613 and 1336 cm −1 , respectively) are slightly smaller than those of 3TT-SSe (1644 and 1378 cm −1 ), indicating an INI combination-induced molecular rigidity enhancement, which is beneficial for suppressing non-radiative energy loss (Δ E nr ) in OSCs [ 63 , 64 ]. To corroborate the enhanced molecular rigidity, reorganization energies for exciton energy transfer ( λ EET ) and electron transport ( λ ET ) were calculated (Fig. 3c and Fig. S13 , Table S11 ). The λ EET values for 3TT-SSe and 3TT-SeS were found to be 130.58 and 115.63 meV, respectively, aligning with the observed trend in Stokes-shift values. Furthermore, 3TT-SeS exhibited a lower λ ET (182.17 meV) than 3TT-SSe (199.33 meV), facilitating efficient charge transport according to the Marcus theory [ 65 ]. Figure 3. Open in a new tab Photophysical properties and stacking behavior. (a) Normalized UV–vis absorption and photoluminescence spectra of 3TT-SSe and 3TT-SeS in dilute chloroform solutions. (b) Absorption spectra in thin films. (c) Calculated reorganization energies for exciton energy transfer (EET) and electron transport (ET) processes. (d) Time-dependent contour maps of in-situ UV–vis absorption spectra for the 3TT-SeS film. (e) 2D-GIWAXS pattern of the neat 3TT-SeS film. (f) In-plane (dashed lines) and out-of-plane (solid lines) line-cut profiles of the 2D-GIWAXS data. The electrochemical properties of the two NFREAs were investigated by cyclic voltammetry experiments ( Fig. S14 ). The energy levels of the lowest unoccupied molecular orbital ( E LUMO ) and highest occupied molecular orbital ( E HOMO ) were estimated to be −4.08 and −5.58 eV for 3TT-SSe, and −4.04 and −5.60 eV for 3TT-SeS, respectively. Furthermore, the HOMO levels determined by ultraviolet photoelectron spectroscopy are −5.62 and −5.64 eV ( Fig. S15 ), respectively. Based on the optical bandgaps (1.34 and 1.37 eV) derived from the absorption onset, the corresponding LUMO levels are calculated to be −4.28 and −4.27 eV. The high-lying E LUMO of 3TT-SeS is consistent with DFT calculations ( Fig. S16 ), thus potentially achieving a higher open-circuit voltage ( V oc ) in corresponding OSCs. Furthermore, in-situ UV–vis absorption spectra (Fig. 3d and Fig. S17 ) during film formation demonstrated accelerated crystallization dynamics for 3TT-SeS, contributing to the establishment of an ordered molecular arrangement. Two-dimensional grazing incidence wide-angle X-ray scattering (2D-GIWAXS) revealed a shorter lamellar stacking distance and decreased π–π stacking distance for 3TT-SeS (18.48 and 3.67 Å) than 3TT-SSe (20.27 and 3.74 Å), consistent with its denser packing and higher molar extinction coefficient of 3TT-SeS (Fig. 3e–f and Fig. S18 , Table S12 ). Subsequently, the crystal coherence length (CCL) and the paracrystalline disorder factor ( g -factor) were calculated to be 16.61 Å/0.189 for 3TT-SSe and 25.13 Å/0.152 for 3TT-SeS, respectively. The increased CCL and reduced g -factor further highlight the role of the INI combination strategy in promoting a tighter and more ordered structure in 3TT-SeS thin film. Photovoltaic performance and device physics To explore the photovoltaic performance of two NFREAs, we fabricated OSC devices featuring an architecture of indium tin oxide/2PACz/active layer/PDINN-S/Ag, utilizing polymer D18 ( Figs S19–S20 ) as the donor material. Following established solvent processing principles [ 11 ], we employed a chloroform/ o -xylene ( o -XY) co-solvent system with a volume ratio of 0.88 : 0.12 to optimize NFREA-based OSCs ( Fig. S21 ). The optimized device parameters and detailed optimization procedures are summarized in Tables 1 and Tables S13–S14 . As demonstrated in Fig. 4a and Fig. S22 , the 3TT-SSe-based device exhibited a moderate PCE of 16.17%, accompanied by a V oc of 0.900 V, a short-circuit current density ( J sc ) of 24.22 mA cm −2 , and a fill factor (FF) of 74.20%. Remarkably, the 3TT-SeS-based device achieved superior photovoltaic performance with simultaneous increases in V oc to 0.925 V, J sc to 25.47 mA cm −2 , and FF to 78.21%, thus yielding a high PCE of 18.44%. The improved J sc value was further supported by the consistency between the external quantum efficiency (EQE) spectra and the absorption spectra of the blend films ( Figs S23–S24 ), showing integrated J sc values of 25.10 and 23.77 mA cm −2 for the D18:3TT-SSe and D18:3TT-SeS devices, respectively. To further unlock the potential of 3TT-SeS with reduced S conf. , we incorporated a reported NFREA 3TTB-ClF [ 26 ] as a guest acceptor into the binary D18:3TT-SeS host blend. This strategy resulted in a significant boost in the PCE of the 3TT-SeS-based device to 19.26% (independently certified as 18.75% by the National Photovoltaic Industry Metrology and Testing Center (NPVM), China; Figs S25–S28 ), representing a record-high efficiency for low-cost NFREA-based OSCs. To evaluate operational stability, encapsulated devices were subjected to continuous one-sun illumination in a nitrogen atmosphere. The NFREA-based devices retained ∼80% of their initial PCEs after 700 h, demonstrating their promising photostability for practical applications ( Fig. S29 ). Table 1. Detailed photovoltaic device parameters of the optimized OSCs. Active layers V oc (V) J sc (mA cm −2 ) calc. J sc ( a) (mA cm −2 ) FF (%) PCE ( b) (%) D18:3TT-SSe 0.900 (0.900 ± 0.001) 24.22 (24.01 ± 0.22) 23.77 74.20 (74.90 ± 0.31) 16.17 (16.05 ± 0.11) D18:3TT-SeS 0.925 (0.824 ± 0.001) 25.47 (25.20 ± 0.26) 25.10 78.21 (77.98 ± 0.24) 18.44 (18.31 ± 0.10) D18:3TT-SeS: 3TTB-ClF 0.939 (0.939 ± 0.001) 25.63 (25.41 ± 0.23) 25.14 80.03 (79.72 ± 0.30) 19.26 (19.10 ± 0.14) D18:3TT-SeS: 3TTB-ClF ( c) 0.938 25.11 — 79.60 18.75 Open in a new tab (a) The J sc values calculated from the EQE curves (b) The error bars correspond to the standard deviation of 30 independent devices; (c) Certified by NPVM, China. Figure 4. Open in a new tab Photovoltaic performance and device physics. (a) J – V characteristics for optimized OSCs. (b) Statistics of C g and CPK values for active-layer materials. (c) E loss value against PCE plots based on the reported efficient NFREA-based OSCs (the list of data is available in Supplementary Table 24 ). (d) J ph – V eff plots of the D18:3TT-SSe- and D18:3TT-SeS-based devices. (e) Statistical diagram of charge transport properties. (f) Electron DOS of the two devices. (g–i) 2D color plots of TA spectra (g), representative TA spectra recorded at indicated delay times (h), and TA kinetic probed at 590 and 780 nm (i) for the 3TT-SeS-based blend film. To evaluate the commercial viability of low- S conf. NFREA-based OSCs, we conducted a comprehensive cost analysis ( C g , cost-per-gram) comparing state-of-the-art FREAs with 3TT-SeS. Using an established cost-calculation model [ 17 ] (Fig. 4b ), we determined the C g values for each material ( Figs S30–S39 and Tables S15–S25 for detailed synthesis schemes and calculations). Remarkably, 3TT-SeS demonstrates a significant cost advantage with a C g of 61.69$ g −1 , achieving >90% reduction relative to reported high-performance FREAs (518.10, 3263.32, and 1352.50$ g −1 for L8-BO, L8-BO-C 4 , and BTP-C3F, respectively). To better assess commercial potential, we further calculated the power generation cost (cost-per-kilowatt, CPK, $ kW −1 ) for active-layer materials. Compared with reference systems (D18: L8-BO: Z8, 4.20$ kW −1 at 20.20% PCE; PM6: L8-BO-C 4 : L8-BO-C 4 -Br, 9.01$ kW −1 at 20.42% PCE; and D18-Cl: BTP-C3F, 3.69$ kW −1 at 20.80% PCE), 3TT-SeS-based blend system shows exceptional cost-performance, with a notably low CPK of 0.77$ kW −1 . This dramatic cost reduction, achieved through our S conf. -oriented molecular design paradigm, highlights the great potential in the development of cost-effective NFREA-based OSCs. To elucidate the origin of V oc enhancement, we conducted a comprehensive energy loss ( E loss ) analysis ( Table S27 and Fig. S40 ). Bandgap ( E g ) determinations via UV–vis/PL spectral crossover revealed E g values of 1.428 eV (3TT-SSe) and 1.444 eV (3TT-SeS) ( Fig. S41 ). Therefore, the calculated total E loss values of 0.528 eV (D18:3TT-SSe) and 0.519 eV (D18:3TT-SeS), derived from E loss = E g — qV oc , demonstrate that the 3TT-SeS-based binary system achieves the smallest reported E loss (0.519 eV) among high-performance NFREA-based OSCs with PCEs exceeding 15% (Fig. 4c and Table S26 ). Furthermore, the non-radiative energy loss (Δ E nr ), determined by the EQE of electroluminescence devices (EQE EL ), is considered the primary contributor to E loss in OSCs. The EQE EL values were found to be 2.16 × 10 −4 and 2.87 × 10 −4 for the devices based on D18:3TT-SSe and D18:3TT-SeS, respectively, demonstrating a strong correlation with the measured solid-state PLQYs of 5.31% (3TT-SSe) and 5.97% (3TT-SeS) [ 66–68 ]. Using the equation Δ E nr = – kT ln(EQE EL ), the corresponding Δ E nr values were calculated to be 0.211 and 0.204 eV for these systems, respectively. The suppressed Δ E nr observed in the 3TT-SeS-based device aligns with the well-documented enhancement in molecular rigidity. To gain a profound understanding of the mechanisms underlying the different J sc and FF observed in the two binary devices, we conducted a systematic investigation of their charge generation and transport processes. The exciton dissociation probability ( P diss ) was assessed by analyzing the correlation between the photocurrent density ( J ph ) and the effective voltage ( V eff ). As shown in Fig. 4d , the D18:3TT-SeS exhibits a higher P diss value of 98.2% compared to the 3TT-SSe-based device (97.4%), enabling a greater probability of and thus leading to the improved J sc . Besides, space-charge-limited current measurements (Figs 4e and S42 ) demonstrated improved and balanced charge transport in the D18:3TT-SeS-based device, with hole/electron mobilities ( μ h / μ e ) of 5.05/4.83 × 10 −4 cm 2 V −1 s −1 ( μ h / μ e ratio = 1.05) vs. 4.17/3.02 × 10 −4 cm 2 V −1 s −1 (ratio = 1.38) for D18:3TT-SSe. The optimized charge transport in the 3TT-SeS-based device facilitates reduce charge accumulation and recombination, thereby contributing to the observed improvements in both J sc and FF. To investigate the charge recombination kinetics, we systematically analyzed the dependences of V oc and J sc on light-intensity ( P light ) ( Fig. S43 ). The relationships follow V oc ∝ ( nk B T / q )ln( P light ) and J sc ∝ ( P light ) α , where k B is the Boltzmann constant, T is the absolute temperature, and q is the elementary charge. For the 3TT-SSe-based device, the n / α values were found to be 1.29/0.96 and 1.11/0.99 for 3TT-SSe and 3TT-SeS-based device, respectively. These values approaching unity indicate suppressed trap-assisted recombination and bimolecular recombination in the D18:3TT-SeS device. Transient photovoltage (TPV) and transient photocurrent measurements revealed an extended charge carrier lifetime (τ = 7.98 μs), enhanced charge carrier density, reduced recombination exponent ( R = 2.36), and lowered nongeminate recombination rate coefficient ( k = 1.20 × 10 −16 m 3 s −1 ) in the 3TT-SeS-based device ( Fig. S44 ). Further insight into the electron states was gained through capacitance-derived density of states (DOS) analysis. The electron DOS distribution follows , where g ( E ) is obtained by extracting from ; N t represents the total density per unit volume; and E t is the energy for the exponential tail distribution that characterizes energetic disorder. As shown in Fig. 4f , the 3TT-SeS blend exhibits a high N t of 5.14 × 10 18 cm −3 and a lower E t of 83.5 meV compared to the 3TT-SSe counterpart (4.14 × 10 18 cm −3 for N t and 90.5 meV for E t ). The enhanced carrier density and reduced energetic disorder correlates with the suppressed energy loss observed in the 3TT-SeS-based device. Hole-transfer (HT) dynamics were probed through transient absorption spectroscopy, in which an excitation wavelength of 780 nm was employed to selectively excite acceptors (Figs 4g and S45 ). Upon photoexcitation, immediate ground state bleaching signals (>650 nm) of the acceptors decayed, accompanied by donor-specific bleaching emergence (520–600 nm), indicating the existence of an HT channel that facilitates exciton dissociation in blend films (Fig. 4h ). Biexponential fitting of kinetics (Fig. 4i ) revealed two distinct processes: the ultrafast exciton dissociation at the donor/acceptor interface (τ 1 ) and slower exciton diffusion in the donor phase toward the interface before dissociation (τ 2 ). Notably, the 3TT-SeS blend exhibited accelerated dynamics with τ 1 = 0.26 ps and τ 2 = 5.61 ps, surpassing the 3TT-SSe counterpart (τ 1 = 0.74 ps, τ 2 = 8.30 ps). These findings indicate a superior hole transfer process in the D18:3TT-SeS blend, aligning with the excellent performance. Micromorphology characterization The molecular dynamics (MD) simulations were employed to investigate the microstructure of blend films. Figure 5a presents equilibrium-state snapshots of the simulated molecular blends. To quantitatively analyze phase separation behavior, we calculated the donor–acceptor centroid distance distribution and obtained the corresponding average values (Fig. 5b ). The results reveal a significantly shorter average centroid distance in the D18:3TT-SeS blend (2.48 Å) compared to the D18:3TT-SSe system (4.47 Å), suggesting the formation of a more compact and ordered microstructure with enhanced separation between D18 and 3TT-SeS components. Surface morphology and phase-separation patterns were probed through atomic force microscopy (AFM) and AFM-coupled infrared spectroscopy (AFM-IR). As shown in Fig. 5c , the root-mean-square roughness ( R q ) of the 3TT-SSe- and 3TT-SeS- based blend films were determined to be 1.20 and 1.37 nm, respectively, suggesting a more pronounced surface crystallization in the D18:3TT-SeS film. Complementary characterization through Fourier-transform infrared spectroscopy ( Fig. S46 ) identified distinct vibrational features for the donor (1579 cm −1 ) and acceptor (1148 cm −1 ) components. Advanced AFM-IR phase analysis ( Fig. S47 ) revealed both D18 and 3TT-SeS formed a denser fibrillar network structure in the 3TT-SeS blend compared to the 3TT-SSe blend. The further overlay analysis (Fig. 5d ) demonstrated entangled donor/acceptor fibrillar domains and higher-quality bicontinuous interpenetrating network morphology observed in the D18:3TT-SeS blend film. The molecular stacking characteristics of both blend films were investigated using 2D-GIWAXS (Figs 5e and S48 , Table S28 ). The blend films exhibited the preferential face-on orientation observed in their neat counterparts, with π–π stacking distances of 3.79 Å for the 3TT-SSe blend and 3.74 Å for the 3TT-SeS film. Notably, the 3TT-SeS-based blend demonstrated superior structural ordering, as evidenced by its increased CCL (21.67 Å) and reduced g -factor (0.166) compared to the 3TT-SSe counterpart (CCL = 13.96 Å, g -factor = 0.208). These results demonstrate that 3TT-SeS, with its lower S conf. , promotes tighter molecular packing and favorable film micromorphology, thus providing a more efficient charge transport pathway and rationalizing the improved J sc and FF in corresponding OSC device. Figure 5. Open in a new tab Micromorphology characterization of blend films. (a) Snapshots of MD simulation (blue and green balls represent donor and acceptor molecules, respectively). (b) Statistical diagram of donor–acceptor centroid distance of the two blend systems. (c) AFM height images (2 μm × 2 μm) (insets are phase images of 1 μm × 1 μm size). (d) The combined AFM-IR images of the two blend films. (e) 2D-GIWAXS patterns for D18:3TT-SSe and D18:3TT-SeS, respectively. CONCLUSION In this work, we proposed a low- S conf. design of NFREAs for highly cost-effective OSCs. Through comprehensive DFT calculations, we identified 3TT-SeS as an optimal low- S conf. and low-cost NFREA via an INI combination strategy. Both theoretical and experimental investigations confirmed that the 3TT-SeS indeed achieves an ultralow S conf. (0.162 J mol −1 K −1 ) and a unique conformer-free state, thus yielding densely ordered crystal packing, along with improved charge transport property and suppressed energetic disorder. These advancements enabled 3TT-SeS-based OSCs to achieve a remarkable PCE of 19.26% (independently certified at 18.75%) in ternary devices, setting a new efficiency benchmark for low-cost OSCs. Importantly, the MOC of 3TT-SeS-based OSC was much lower than that of the state-of-the-art FREA-based systems. This breakthrough not only addresses the long-standing trade-off between cost and efficiency in organic photovoltaics but also presents a scalable, industrially viable strategy for developing next-generation organic semiconductors. MATERIALS AND METHODS Detailed materials and methods are available in the online supplementary data . Supplementary Material nwag177_Supplemental_Files nwag177_supplemental_files.zip (8.5MB, zip) ACKNOWLEDGEMENTS This work was supported by the Shanghai Frontiers Science Center of Molecule Intelligent Syntheses. The authors also thank Wuxi Seniormaterial and Scientific Compass ( www.shiyanjia.com ) for their support in the key chemicals and single-crystal diffractions. Contributor Information Xiaobin Gu, College of Materials Science and Opto-Electronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 101408, China. Rui Zeng, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, China. Fei Han, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, China. Jing Li, Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, Shanghai Frontiers Science Center of Molecule Intelligent Syntheses, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200241, China. Senke Tan, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, China. Jikai Lv, College of Materials Science and Opto-Electronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 101408, China. Na Yu, Center for Advanced Low-Dimension Materials, State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, China. Lixuan Kan, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, China. Hao Li, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, China. Yuqi Hou, College of Materials Science and Opto-Electronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 101408, China. Yunhao Cai, College of Materials Science and Opto-Electronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 101408, China. Zhixiang Wei, Center for Excellence in Nanoscience (CAS), Key Laboratory of Nanosystem and Hierarchical Fabrication (CAS), National Center for Nanoscience and Technology, Beijing 100190, China. Zheng Tang, Center for Advanced Low-Dimension Materials, State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, China. Lianrui Hu, Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, Shanghai Frontiers Science Center of Molecule Intelligent Syntheses, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200241, China. Feng Liu, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, China. Xin Zhang, College of Materials Science and Opto-Electronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 101408, China. Hui Huang, College of Materials Science and Opto-Electronic Technology, Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 101408, China; School of Chemical Engineering and Technology, State Key Laboratory of Chemical Engineering and Low-Carbon Technology, Tianjin University, Tianjin 300072, China; The International Joint Institute of Tianjin University, Fuzhou 350205, China. FUNDING This work was supported by the National Natural Science Foundation of China (52120105006 and 52473326), the National Key R&D Program of China (2024YFB3614300), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB0520103), the Youth Innovation Promotion Association of Chinese Academy of Sciences (2022165), the Fundamental Research Funds for the Central Universities, and the Xiaomi Young Talents Program. AUTHOR CONTRIBUTIONS Hui Huang, Xin Zhang, and Feng Liu supervised and directed this project. Xiaobin Gu conceived the idea, designed and synthesized the NFREAs, and carried out the detailed characterizations. Rui Zeng fabricated and characterized the devices. Fei Han and Senke Tan provided energy loss analysis and TPV/TPV measurement. Jing Li and Lianrui Hu performed the MD simulations. Na Yu and Zheng Tang conducted energy loss analysis. Jikai Lv performed NBO calculation and analysis. Lixuan Kan and Hao Li provided TA measurement and corresponding analysis. Yunhao Cai helped with device characterization. Yuqi Hou performed the PL measurements. Zhixiang Wei performed 2D-GIWAXS measurement. Xiaobin Gu, Xin Zhang, and Hui Huang prepared the manuscript. All authors discussed the results and commented on the manuscript Conflict of interest statement . None declared. REFERENCES 1. Zhang  J, Tan  HS, Guo  X  et al.  Material insights and challenges for non-fullerene organic solar cells based on small molecular acceptors. Nat Energy  2018; 3: 720–31. 10.1038/s41560-018-0181-5 [ DOI ] [ Google Scholar ] 2. Cheng  P, Li  G, Zhan  X  et al.  Next-generation organic photovoltaics based on non-fullerene acceptors. Nat Photon  2018; 12: 131–42. 10.1038/s41566-018-0104-9 [ DOI ] [ Google Scholar ] 3. Grandhi  GK, Koutsourakis  G, Blakesley  JC  et al.  Promises and challenges of indoor photovoltaics. Nat Rev Clean Technol  2025; 1: 132–47. 10.1038/s44359-024-00013-1 [ DOI ] [ Google Scholar ] 4. Wang  J, Xie  Y, Chen  K  et al.  Physical insights into non-fullerene organic photovoltaics. Nat Rev Phys  2024; 6: 365–81. 10.1038/s42254-024-00719-y [ DOI ] [ Google Scholar ] 5. Yi  J, Zhang  G, Yu  H  et al.  Advantages, challenges and molecular design of different material types used in organic solar cells. Nat Rev Mater  2024; 9: 46–62. 10.1038/s41578-023-00618-1 [ DOI ] [ Google Scholar ] 6. Ma  R, Lou  Z, Zhang  Y  et al.  Organic Solar Cells: beyond 20%. Sci China Mater  2025; 68: 1689–701. 10.1007/s40843-025-3366-9 [ DOI ] [ Google Scholar ] 7. Wang  J, Xue  P, Jiang  Y  et al.  The principles, design and applications of fused-ring electron acceptors. Nat Rev Chem  2022; 6: 614–34. 10.1038/s41570-022-00409-2 [ DOI ] [ PubMed ] [ Google Scholar ] 8. Lin  Y, Wang  J, Zhang  Z  et al.  An electron acceptor challenging fullerenes for efficient polymer solar cells. Adv Mater  2015; 27: 1170–4. 10.1002/adma.201404317 [ DOI ] [ PubMed ] [ Google Scholar ] 9. Yuan  J, Zhang  Y, Zhou  L  et al.  Single-junction organic solar cell with over 15% efficiency using fused-ring acceptor with electron-deficient core. Joule  2019; 3: 1140–51. 10.1016/j.joule.2019.01.004 [ DOI ] [ Google Scholar ] 10. Jiang  Y, Sun  S, Xu  R  et al.  Non-fullerene acceptor with asymmetric structure and phenyl-substituted alkyl side chain for 20.2% efficiency organic solar cells. Nat Energy  2024; 9: 975–86. 10.1038/s41560-024-01557-z [ DOI ] [ Google Scholar ] 11. Zeng  R, Zhang  M, Wang  X  et al.  Achieving 19% efficiency in non-fused ring electron acceptor solar cells via solubility control of donor and acceptor crystallization. Nat Energy  2024; 9: 1117–28. [ Google Scholar ] 12. Zhu  L, Zhang  M, Zhou  Z  et al.  Progress of organic photovoltaics towards 20% efficiency. Nat Rev Electr Eng  2024; 1: 581–96. 10.1038/s44287-024-00080-3 [ DOI ] [ Google Scholar ] 13. Zhou  Y, Su  W, Liang  Z  et al.  Halogenated diphenyl ether solvent additives enable ∼20% efficiency organic solar cells and high-performance opaque/semitransparent modules. Natl Sci Rev  2025; 12: nwaf346. 10.1093/nsr/nwaf346 [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] 14. Chen  H, Huang  Y, Zhang  R  et al.  Organic solar cells with 20.82% efficiency and high tolerance of active layer thickness through crystallization sequence manipulation. Nat Mater  2025; 24: 444–53. 10.1038/s41563-024-02062-0 [ DOI ] [ PubMed ] [ Google Scholar ] 15. Li  C, Song  J, Lai  H  et al.  Non-fullerene acceptors with high crystallinity and photoluminescence quantum yield enable >20% efficiency organic solar cells. Nat Mater  2025; 24: 433–43. [ DOI ] [ PubMed ] [ Google Scholar ] 16. Cheng  J, Wang  L, Wang  T  et al.  Vacuum assisted vertical component distribution in pseudo-bulk heterojunctions: a pathway to high performance and stable organic solar cells. Natl Sci Rev  2025; 12: nwaf440. 10.1093/nsr/nwaf440 [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] 17. Yang  N, Zhang  S, Cui  Y  et al.  Molecular design for low-cost organic photovoltaic materials. Nat Rev Mater  2025; 10: 404–24. 10.1038/s41578-025-00792-4 [ DOI ] [ Google Scholar ] 18. Li  G, Al-Hashimi  M, Facchetti  A  et al.  Decoding the halogenation cost-performance paradox in organic solar cells. Nat Rev Mater  2025; 10: 617–31. 10.1038/s41578-025-00804-3 [ DOI ] [ Google Scholar ] 19. Li  S, Zhan  L, Liu  F  et al.  An unfused-core-based nonfullerene acceptor enables high-efficiency organic solar cells with excellent morphological stability at high temperatures. Adv Mater  2018; 30: 1705208. 10.1002/adma.201705208 [ DOI ] [ PubMed ] [ Google Scholar ] 20. Huang  H, Guo  Q, Feng  S  et al.  Noncovalently fused-ring electron acceptors with near-infrared absorption for high-performance organic solar cells. Nat Commun  2019; 10: 3038. 10.1038/s41467-019-11001-6 [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] 21. Liu  X, Wei  Y, Zhang  X  et al.  An A-D-A’-D-A type unfused nonfullerene acceptor for organic solar cells with approaching 14% efficiency. Sci China Chem  2021; 64: 228–31. 10.1007/s11426-020-9868-8 [ DOI ] [ Google Scholar ] 22. Yang  N, Cui  Y, Zhang  T  et al.  Molecular design of fully nonfused acceptors for efficient organic photovoltaic cells. J Am Chem Soc  2024; 146: 9205–15. 10.1021/jacs.4c00090 [ DOI ] [ PubMed ] [ Google Scholar ] 23. Shen  Q, He  C, Li  S  et al.  Design of non-fused ring acceptors toward high-performance, stable, and low-cost organic photovoltaics. Acc Mater Res  2022; 3: 644–57. 10.1021/accountsmr.2c00052 [ DOI ] [ Google Scholar ] 24. Jiang  P, Liu  Y, Song  J  et al.  Emergence of low-cost and high-performance nonfused ring electron acceptors. Acc Chem Res  2024; 57: 3419–32. 10.1021/acs.accounts.4c00592 [ DOI ] [ PubMed ] [ Google Scholar ] 25. Gu  X, Zeng  R, He  T  et al.  Simple-structured acceptor with highly interconnected electron-transport pathway enables high-efficiency organic solar cells. Adv Mater  2024; 36: 2401370. 10.1002/adma.202401370 [ DOI ] [ PubMed ] [ Google Scholar ] 26. Gu  X, Zeng  R, Hou  Y  et al.  Precisely regulating intermolecular interactions and molecular packing of nonfused-ring electron acceptors via halogen transposition for high-performance organic solar cells. Angew Chem Int Ed  2024; 63: e202407355. 10.1002/anie.202407355 [ DOI ] [ PubMed ] [ Google Scholar ] 27. Gao  J, Zhu  X, Bao  H  et al.  Latest progress on fully non-fused electron acceptors for high-performance organic solar cells. Chin Chem Lett  2023; 34: 107968. 10.1016/j.cclet.2022.107968 [ DOI ] [ Google Scholar ] 28. Wang  X, Wei  N, Chen  Y  et al.  Highly efficient and stable binary and ternary organic solar cells using polymerized nonfused ring electron acceptors. Natl Sci Rev  2024; 11: nwae258. 10.1093/nsr/nwae258 [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] 29. Huang  H, Chen  Z, Ponce Ortiz  R  et al.  Combining electron-neutral building blocks with intramolecular “conformational locks” affords stable, high-mobility p- and n-channel polymer semiconductors. J Am Chem Soc  2012; 134: 10966–73. 10.1021/ja303401s [ DOI ] [ PubMed ] [ Google Scholar ] 30. Huang  H, Yang  L, Facchetti  A  et al.  Organic and polymeric semiconductors enhanced by noncovalent conformational locks. Chem Rev  2017; 117: 10291–318. 10.1021/acs.chemrev.7b00084 [ DOI ] [ PubMed ] [ Google Scholar ] 31. Liu  Y, Zhang  Z, Feng  S  et al.  Exploiting noncovalently conformational locking as a design strategy for high performance fused-ring electron acceptor used in polymer solar cells. J Am Chem Soc  2017; 139: 3356–9. 10.1021/jacs.7b00566 [ DOI ] [ PubMed ] [ Google Scholar ] 32. Ma  L, Zhang  S, Zhu  J  et al.  Completely non-fused electron acceptor with 3D-interpenetrated crystalline structure enables efficient and stable organic solar cell. Nat Commun  2021; 12: 5093. 10.1038/s41467-021-25394-w [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] 33. Wang  X, Lu  H, Liu  Y  et al.  Simple nonfused ring electron acceptors with 3d network packing structure boosting the efficiency of organic solar cells to 15.44%. Adv Energy Mater  2021; 11: 2102591. 10.1002/aenm.202102591 [ DOI ] [ Google Scholar ] 34. Zhang  X, Gu  X, Huang  H. Low-cost nonfused-ring electron acceptors enabled by noncovalent conformational locks. Acc Chem Res  2024; 57: 981–91. 10.1021/acs.accounts.3c00813 [ DOI ] [ PubMed ] [ Google Scholar ] 35. Rubinstein  M, Colby  RH. Polymer Physics. Oxford: Oxford University Press, 2003. 10.1093/oso/9780198520597.001.0001 [ DOI ] [ Google Scholar ] 36. Flory  PJ. Statistical Mechanics of Chain Molecules. New York, NY: Interscience Publishers, 1969. 10.1002/bip.1969.360080514 [ DOI ] [ Google Scholar ] 37. Dai  X, Wan  H, Zhang  X  et al.  Role of conformational entropy in complex macromolecular systems. Chem Res Chin Univ  2023; 39: 709–18. 10.1007/s40242-023-3174-2 [ DOI ] [ Google Scholar ] 38. Skriver  K, Theisen  FF, Kragelund  BB. Conformational entropy in molecular recognition of intrinsically disordered proteins. Curr Opin Struct Biol  2023; 83: 102697. 10.1016/j.sbi.2023.102697 [ DOI ] [ PubMed ] [ Google Scholar ] 39. Boltzmann  L. Vorlesungen über Gastheorie. Bd. 1.  Leipzig: Barth, 1896. [ Google Scholar ] 40. Brady  GP, Sharp  KA. Entropy in protein folding and in protein–protein interactions. Curr Opin Struct Biol  1997; 7: 215–21. 10.1016/S0959-440X(97)80028-0 [ DOI ] [ PubMed ] [ Google Scholar ] 41. Sawatzki-Park  M, Wang  S, Kleemann  H  et al.  Highly ordered small molecule organic semiconductor thin-films enabling complex, high-performance multi-junction devices. Chem Rev  2023; 123: 8232–50. 10.1021/acs.chemrev.2c00844 [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] 42. Spolar  RS, Record  MT. Coupling of local folding to site-specific binding of proteins to DNA. Science  1994; 263: 777–84. 10.1126/science.8303294 [ DOI ] [ PubMed ] [ Google Scholar ] 43. Frederick  KK, Marlow  MS, Valentine  KG  et al.  Conformational entropy in molecular recognition by proteins. Nature  2007; 448: 325–9. 10.1038/nature05959 [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] 44. Tzeng  S-R, Kalodimos  CG. Protein activity regulation by conformational entropy. Nature  2012; 488: 236–40. 10.1038/nature11271 [ DOI ] [ PubMed ] [ Google Scholar ] 45. Yao  Z-F, Wang  J, Pei  J. Controlling morphology and microstructure of conjugated polymers via solution-state aggregation. Prog Polym Sci  2023; 136: 101626. 10.1016/j.progpolymsci.2022.101626 [ DOI ] [ Google Scholar ] 46. Ding  L, Yu  Z-D, Wang  X  et al.  Polymer semiconductors: synthesis, processing, and applications. Chem Rev  2023; 123: 7421–97. 10.1021/acs.chemrev.2c00696 [ DOI ] [ PubMed ] [ Google Scholar ] 47. Bronstein  H, Nielsen  CB, Schroeder  BC  et al.  The role of chemical design in the performance of organic semiconductors. Nat Rev Chem  2020; 4: 66–77. 10.1038/s41570-019-0152-9 [ DOI ] [ PubMed ] [ Google Scholar ] 48. Wu  J, Torresi  L, Hu  M  et al.  Inverse design workflow discovers hole-transport materials tailored for perovskite solar cells. Science  2024; 386: 1256–64. 10.1126/science.ads0901 [ DOI ] [ PubMed ] [ Google Scholar ] 49. Tran  H, Gurnani  R, Kim  C  et al.  Design of functional and sustainable polymers assisted by artificial intelligence. Nat Rev Mater  2024; 9: 866–86. 10.1038/s41578-024-00708-8 [ DOI ] [ Google Scholar ] 50. Liu  M, Han  X, Chen  H  et al.  A molecular descriptor of intramolecular noncovalent interaction for regulating optoelectronic properties of organic semiconductors. Nat Commun  2023; 14: 2500. 10.1038/s41467-023-38078-4 [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] 51. Yan  X, Xiong  M, Deng  X  et al.  Approaching disorder-tolerant semiconducting polymers. Nat Commun  2021; 12: 5723. 10.1038/s41467-021-26043-y [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] 52. Che  Y, Perepichka  DF. Quantifying planarity in the design of organic electronic materials. Angew Chem Int Ed  2021; 60: 1364–73. 10.1002/anie.202011521 [ DOI ] [ PubMed ] [ Google Scholar ] 53. Wang  CS, Burkett  J, Lee  CY-C  et al.  Structure and electrical conductivity of ion-implanted rigid-rod and ladder polymers. J Polym Sci B Polym Phys  1993; 31: 1799–807. 10.1002/polb.1993.090311213 [ DOI ] [ Google Scholar ] 54. Ji  Y, Oka  M, Honda  S. Synthesis of reversibly photocleavable pseudo-ladder polymers. Prog Chem  2021; 12: 4621–5. [ Google Scholar ] 55. Zhang  Q, Huang  J, Wang  K  et al.  Recent structural engineering of polymer semiconductors incorporating hydrogen bonds. Adv Mater  2022; 34: 2110639. 10.1002/adma.202110639 [ DOI ] [ PubMed ] [ Google Scholar ] 56. Yu  X, Li  C, Gao  C  et al.  Incorporation of hydrogen-bonding units into polymeric semiconductors toward boosting charge mobility, intrinsic stretchability, and self-healing ability. SmartMat  2021; 2: 347–66. 10.1002/smm2.1062 [ DOI ] [ Google Scholar ] 57. Zhu  C, Kalin  AJ, Fang  L. Covalent and noncovalent approaches to rigid coplanar π-conjugated molecules and macromolecules. Acc Chem Res  2019; 52: 1089–100. 10.1021/acs.accounts.9b00022 [ DOI ] [ PubMed ] [ Google Scholar ] 58. Ren  J, Bi  P, Zhang  J  et al.  Molecular design revitalizes the low-cost PTV-polymer for highly efficient organic solar cells. Natl Sci Rev  2021; 8: nwab031. 10.1093/nsr/nwab031 [ DOI ] [ PMC free article ] [ PubMed ] [ Google Scholar ] 59. Tian  L. Molclus Program, Version 1.9.9.9. http://www.keinsci.com/research/molclus.html (6 March 2022, date last accessed). 60. Fan  B, Lin  F, Wu  X  et al.  Selenium-containing organic photovoltaic materials. Acc Chem Res  2021; 54: 3906–16. 10.1021/acs.accounts.1c00443 [ DOI ] [ PubMed ] [ Google Scholar ] 61. Lai  H, He  F. Crystal engineering in organic photovoltaic acceptors: a 3D network approach. Adv Energy Mater  2020; 10: 2002678. 10.1002/aenm.202002678 [ DOI ] [ Google Scholar ] 62. Han  Z, Ce  Z, He  T  et al.  Precisely manipulating molecular packing via tuning alkyl side-chain topology enabling high-performance nonfused-ring electron acceptors. Angew Chem Int Ed  2024; 63: e202318143. 10.1002/anie.202318143 [ DOI ] [ PubMed ] [ Google Scholar ] 63. Gu  X, Wei  Y, Zeng  R  et al.  Suppressing exciton–vibration coupling via intramolecular noncovalent interactions for low-energy-loss organic solar cells. Angew Chem Int Ed  2025; 64: e202418926. 10.1002/anie.202418926 [ DOI ] [ PubMed ] [ Google Scholar ] 64. Gu  X, Wei  Y, Yu  N  et al.  High-efficiency and low-energy-loss organic solar cells enabled by tuning conformations of dimeric electron acceptors. CCS Chem  2023; 5: 2576–88. 10.31635/ccschem.023.202202575 [ DOI ] [ Google Scholar ] 65. Marcus  RA. Electron transfer reactions in chemistry: theory and experiment (Nobel lecture). Angew Chem Int Ed Engl  1993; 32: 1111–21. 10.1002/anie.199311113 [ DOI ] [ Google Scholar ] 66. Chen  X, Qian  D, Wang  Y  et al.  A unified description of non-radiative voltage losses in organic solar cells. Nat Energy  2021; 6: 799–806. 10.1038/s41560-021-00843-4 [ DOI ] [ Google Scholar ] 67. Lu  H, Li  D, Liu  W  et al.  Designing A–D–A type fused-ring electron acceptors with a bulky 3D substituent at the central donor core to minimize non-radiative losses and enhance organic solar cell efficiency. Angew Chem Int Ed  2024; 63: e202407007. 10.1002/anie.202407007 [ DOI ] [ PubMed ] [ Google Scholar ] 68. Wei  N, Guo  Y, Song  H  et al.  Reducing non-radiative energy losses in non-fullerene organic solar cells. ChemSusChem  2025; 18: e202402169. 10.1002/cssc.202402169 [ DOI ] [ PubMed ] [ Google Scholar ] Associated Data This section collects any data citations, data availability statements, or supplementary materials included in this article. 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