Miscibility Regulation and Thermal Annealing Induced Hierarchical Morphology Enables High‐Efficiency All‐Small‐Molecule Organic Solar Cells Over 17%

Abstract Achieving an ideal morphology to realize efficient charge generation and transport is an imperative avenue to improve the photovoltaic performance of all small‐molecule organic solar cells (SM‐OSCs). Here, ternary SM‐OSCs are fabricated based on a new small molecule donor, SM‐mB, and an alloyed blend acceptor of Y6 and its derivative, L8‐BO, and desirable hierarchical morphology with appropriate nanoscale phase separation is successfully realized through adjusting the thermal annealing treatment conditions and compositions of mixed acceptors in the active layer. Then the ternary SM‐OSCs achieve an excellent PCE of 17.06 %, which is one of the best results for the SM‐OSCs so far. The desirable morphology can be ascribed to the optimization of the miscibility‐driven donor and acceptor blend morphology that takes full advantage of the individual advantages of both acceptors, which facilitate efficient charge generation and extraction with more balanced charge carrier mobilities. More importantly, the photovoltaic performance of the ternary SM‐OSCs possesses a high tolerance to the device fabrication conditions, including thermal annealing treatment, and is insensitive to film thickness, which is beneficial for large‐area manufacture and future practical applications.