Multi‐Trifluoromethylated Benzotriazole‐Based Acceptor: Induced Molecular Orderly Packing Achieving High‐Performance Planar‐Mixed Heterojunction Organic Photovoltaics

In planar‐mixed heterojunction organic solar cells (PMHJ‐OSCs), efficient exciton utilization remains a significant challenge due to the limited diffusion distance of excitons. Achieving an optimized morphology in the active layer is essential for facilitating both exciton diffusion and charge carrier transport. In this work, the challenge is addressed by employing a dual strategy involving the development of a novel acceptor BTz‐CF3 and ternary PMHJ blending. By mixing BTz‐CF3 in the acceptor L8‐BO layer, PMHJ‐OSCs based on D18/L8‐BO:BTz‐CF3 with a more ideal vertical phase separation showed an efficiency of 18.6%, higher than that of 18.2% for the D18/L8‐BO control system. Interestingly, introducing BTz‐CF3 in the donor D18 layer could facilitate the penetration of L8‐BO into the donor layer while simultaneously induced the L8‐BO orderly stacking within the upper layer, showing a unique advantage in constructing improved morphology in the PMHJ active layer. As a result, the D18:BTz‐CF3/L8‐BO PMHJ‐device achieved an excellent efficiency of 19.5%. This work demonstrates that the strategy of incorporating a well‐miscible third component into the donor layer has great potential in fabricating efficient PMHJ OSCs by improving molecular stacking and vertical distribution.