Cleaving Fused-Ring Conjugated Structure and Introducing Aggregation-Induced Emission Effect Enable over 20% Efficiency Organic Solar Cells

How to reduce energy loss by enhancing the photoluminescence quantum yield (PLQY) is currently one big bottleneck to further increase the open-circuit voltage ( V OC ) and power conversion efficiency (PCE) of organic solar cells (OSCs). Utilizing the aggregation-induced emission (AIE) effect should be effective to enhance the PLQY. However, there is no reliable molecular design strategy to realize AIE while maintaining the appropriate aggregation behavior of materials. In this study, through cleavage of the conjugated structure of the shamrock-shaped molecule of AQ-fNI, a nonfullerene acceptor (NFA), AQ-NI, with AIE effect was developed. AQ-NI exhibits a higher PLQY (14.6%) than that of AQ-fNI (6.16%), enabling an exceptionally low energy loss of 0.494 eV and consequently a high V OC of 0.960 V. Moreover, the becoming stacking characteristics of AQ-NI facilitate the modulation of aggregation behavior in the active layer, resulting in a favorable phase-separated morphology and enhanced charge carrier transport. As a result, the layer-by-layer (LBL)-fabricated binary OSCs based on D18/AQ-NI achieved a high PCE of 19.14%. In addition, AQ-NI could serve as a guest molecule in a bulk-heterojunction structure, and D18:L8-BO:AQ-NI-based ternary OSCs realized an improved PCE of 20.22% in comparison with the D18:L8-BO-based binary device (PCE = 19.39%). Our findings provide a simple and promising strategy for designing high-performance NFAs with AIE effect and establish a fundamental correlation between AIE properties and OSC performance.