Xiangjian Wan

Core‐asymmetric acceptors, which combine the advantages of electron‐deficient cores and molecular asymmetry, represent a promising yet underexplored design strategy for organic solar cells. Herein, we designed and synthesized two asymmetric 1,2,4‐benzotriazine‐based acceptors, H‐Th and H‐Th‐FN, both featuring a chlorinated thiophene unit side‐grafted onto the central core. The electron‐rich thiophene modulates the strong electron deficiency of the triazine core, while effective orbital overlap enhances molecular rigidity. Notably, H‐Th‐FN incorporates a fluoronaphthalene terminal to achieve dual π‐conjugation extension in the central core and end group, thereby affording a narrower bandgap and weaker electron‐phonon coupling. This structural strategy optimizes intermolecular packing, suppresses aggregation‐caused quenching, and reduces non‐radiative recombination loss to as low as 0.213 eV. As a result, the PM6:H‐Th‐FN binary device achieves a power conversion efficiency of 19.67%, while the corresponding ternary device achieves an impressive efficiency of 20.74%. This work develops a family of 1,2,4‐benzotriazine‐based acceptors for high‐performance organic solar cells, underscoring the advantages of central‐core asymmetry and its broad potential.

The medium-bandgap polymer donor DZ5 regulates spectral utilization, energetic alignment, and morphology in D18 ternary OSCs, reducing energetic disorder and non-radiative loss and achieving a PCE of 20.44%.

Small‐molecule acceptors (SMAs) bearing steric substituents suppress excessive aggregation‐induced nonradiative energy loss (Δ E _nrad ), but this strategy often compromises charge transport by disrupting π‐orbital overlap and blend morphology. This trade‐off remains a key limitation to further improving photovoltaic efficiency. Here, we probe this dilemma through linkage‐topology engineering by incorporating highly crystalline and luminescent 3,6‐dichlorocarbazole units into SMA backbones. Through systematic linker variation, we tune acceptor self‐aggregation and donor/acceptor intermolecular interactions, thereby mitigating this intrinsic trade‐off. By modulating molecular linkage mode from a direct C─N connection (CHC‐1) to a flexible methylene bridge (CHC‐2) and a rigid carbonyl bridge (CHC‐3), we achieve orthogonal control over acceptor aggregation and donor/acceptor interfacial coupling. Notably, carbonyl‐bridged CHC‐3 shows the weakest acceptor self‐association, but the strongest donor/acceptor coupling with PM6. This combination suppresses charge‐transfer‐state nonradiative recombination and optimizes film‐forming kinetics, leading to an improved vertical composition gradient and a refined surface morphology. Consequently, CHC‐3‐based binary and ternary devices achieve PCEs of 18.79% and 20.58%, respectively, with a markedly reduced Δ E _nrad of 0.204 eV. This work establishes linkage‐topology engineering as an effective strategy for balancing luminescence efficiency, charge transport, and morphology in sterically modified SMAs.

Small‐molecule acceptors (SMAs) bearing steric substituents suppress excessive aggregation‐induced nonradiative energy loss (Δ E _nrad ), but this strategy often compromises charge transport by disrupting π‐orbital overlap and blend morphology. This trade‐off remains a key limitation to further improving photovoltaic efficiency. Here, we probe this dilemma through linkage‐topology engineering by incorporating highly crystalline and luminescent 3,6‐dichlorocarbazole units into SMA backbones. Through systematic linker variation, we tune acceptor self‐aggregation and donor/acceptor intermolecular interactions, thereby mitigating this intrinsic trade‐off. By modulating molecular linkage mode from a direct C─N connection (CHC‐1) to a flexible methylene bridge (CHC‐2) and a rigid carbonyl bridge (CHC‐3), we achieve orthogonal control over acceptor aggregation and donor/acceptor interfacial coupling. Notably, carbonyl‐bridged CHC‐3 shows the weakest acceptor self‐association, but the strongest donor/acceptor coupling with PM6. This combination suppresses charge‐transfer‐state nonradiative recombination and optimizes film‐forming kinetics, leading to an improved vertical composition gradient and a refined surface morphology. Consequently, CHC‐3‐based binary and ternary devices achieve PCEs of 18.79% and 20.58%, respectively, with a markedly reduced Δ E _nrad of 0.204 eV. This work establishes linkage‐topology engineering as an effective strategy for balancing luminescence efficiency, charge transport, and morphology in sterically modified SMAs.

Asymmetric molecular design has emerged as an effective strategy for developing high‐performance acceptors for organic solar cells (OSCs). Here, we introduce a dual‐asymmetric topology strategy, in which the stereochemical configurations of both the central core and terminal groups are co‐engineered. Using this approach, we synthesized an isomeric pair, Th2Cl‐a‐2Cl and Th2Cl‐b‐2Cl and benchmarked them against the singly asymmetric a‐CH‐Th2Cl and Th2Cl‐4Cl. We find that the distinctive steric conformation of Th2Cl‐a‐2Cl promotes a geometrically complementary, interlocked packing motif within the crystal lattice. This not only reinforces the three‐dimensional network connectivity but, more importantly, gives rise to a more uniform local electrostatic environment at the molecular‐skeleton scale. As a result, Th2Cl‐a‐2Cl exhibits weaker and more balanced environment‐induced electrostatic fluctuations along the backbone, which helps reduce local electrostatic perturbations during charge transport. Consequently, PM6:Th2Cl‐a‐2Cl devices deliver a champion PCE of 20.18% with a high fill factor (FF) of 80.88%, while significantly suppressing the non‐radiative recombination loss (Δ E ₃ ) to 0.190 eV. These results establish geometric complementarity and electrostatic homogeneity, achieved through topological engineering, as an effective route to improve the efficiency of OSCs.

Fused‐ring trimeric acceptor benefits from both the high symmetry/planarity of small‐molecule acceptors and the large glass transition temperature of polymeric acceptors, making it highly potential to achieve organic solar cells (OSCs) with excellent power conversion efficiencies (PCEs) and long‐term stabilities simultaneously. However, due to the structural complexity of ring‐fused trimeric acceptor, conveniently tuning its optoelectronic properties remains a significant challenge. Herein, the first family of optically and electrostatically tunable fused‐ring trimeric acceptors (CH34, CH35, and CH36) is constructed by incorporating electron‐donating triazatruxene, electron‐neutral triphenylene and electron‐withdrawing tricycloquinazoline as central planes, respectively. All the trimeric acceptors maintain the intrinsic rigidity and planarity of molecular skeleton, which endow them with very small reorganization energies and weak electron–phonon coupling. Moreover, the quite different electrostatic properties of central cores exert significant effects on the energy levels distribution and light harvesting capacity of acceptors. Consequently, CH36 achieves a good PCE of 16.73%, representing the best performance among ring‐fused trimeric acceptors. Remarkably, CH36‐based ternary OSCs further render an excellent PCE of 20.48% along with substantially improved operational stability. Our work demonstrates the great potential of fused‐ring trimeric acceptor for realizing both highly efficient and stable organic photovoltaics.

Fused‐ring trimeric acceptor benefits from both the high symmetry/planarity of small‐molecule acceptors and the large glass transition temperature of polymeric acceptors, making it highly potential to achieve organic solar cells (OSCs) with excellent power conversion efficiencies (PCEs) and long‐term stabilities simultaneously. However, due to the structural complexity of ring‐fused trimeric acceptor, conveniently tuning its optoelectronic properties remains a significant challenge. Herein, the first family of optically and electrostatically tunable fused‐ring trimeric acceptors (CH34, CH35, and CH36) is constructed by incorporating electron‐donating triazatruxene, electron‐neutral triphenylene and electron‐withdrawing tricycloquinazoline as central planes, respectively. All the trimeric acceptors maintain the intrinsic rigidity and planarity of molecular skeleton, which endow them with very small reorganization energies and weak electron–phonon coupling. Moreover, the quite different electrostatic properties of central cores exert significant effects on the energy levels distribution and light harvesting capacity of acceptors. Consequently, CH36 achieves a good PCE of 16.73%, representing the best performance among ring‐fused trimeric acceptors. Remarkably, CH36‐based ternary OSCs further render an excellent PCE of 20.48% along with substantially improved operational stability. Our work demonstrates the great potential of fused‐ring trimeric acceptor for realizing both highly efficient and stable organic photovoltaics.

ConspectusThe innovative exploration of non-fullerene acceptors (NFAs) such as ITIC, Y6, and others, has boosted the power conversion efficiencies (PCEs) of organic solar cells (OSCs) surpassing 21%. However, organic photovoltaics still suffer from significant efficiency gaps compared to inorganic photovoltaics, particularly in open-circuit voltage under similar bandgaps. This notable disparity is largely driven by the stark difference in nonradiative recombination energy losses: OSCs typically incur losses exceeding 0.2 eV, whereas their inorganic counterparts suffer only minimal losses, ranging from a mere 0.03 to 0.04 eV. This insurmountable nonradiative recombination is closely associated with some intrinsic features of organic photovoltaic light-harvesting materials: relatively flexible molecular frameworks, loose and disordered molecular aggregates, large exciton binding energies, etc. Therefore, a multiscale regulation spanning single-molecular properties and aggregation behaviors in further molecular design is required, if a remarkable PCE improvement is expected.In this Account, we first present a brief review of the development of electron acceptor materials, with a focus on analyzing the prominent merits of current high-efficiency acceptor molecular skeletons (especially Y6 analogs) in terms of intermolecular packing modes, photodynamic, etc. Meanwhile, great challenges for further material design also arises from the quite limited structural optimization room for Y-series backbones. In order to break through the dilemma of molecular design, we developed CH-series NFAs with multi-functionalized central units and an "acceptor-donor-acceptor" architecture. Subsequently, a systematic discussion about CH-series NFAs will be made to reveal their advantages in (1) inducing a directional transformation of molecular packing mode toward a more favorable one, through multiple intermolecular weak interactions such as fluorine-hydrogen/sulfur/π bonds, thus rendering multidimensional long-range ordered molecular stacking to minimize energy loss pathways in OSCs; (2) breaking through the limitations of traditional dimeric/trimeric/polymeric acceptor design by pioneering the construction of relatively rigid central-units-linked dimeric/trimeric NFAs with multiple free terminals to enhance intermolecular packings; (3) proposing a novel "functional reconfiguration" strategy for the central units, aiming to explore new photoelectric conversion mechanisms in organic photovoltaic materials.Thus far, CH-series NFAs based binary OSCs have achieved the highest PCE of approaching 21%, ranking among the best NFAs. If further considering their great structural modification possibilities, CH-series NFAs hold exceptional promise as a versatile platform for developing OSCs with record-breaking PCEs. Therefore, we further propose some perspectives for CH-series NFAs, for example, more precise structural and packing optimization to reduce exciton binding energies and improve molecular packing ordering; further in-depth exploration of a "functional reconfiguration" strategy to apply new photoelectric conversion mechanisms, such as triplet excitons, singlet fission, etc.; extending the absorption edge of NFAs to near-infrared II region to harvest more low-energy photons, especially for tandem OSCs. These strategies may have the potential to overcome the critical challenge existing in OSCs and shrink the PCE gap comparing to inorganic platforms.