Central Core Substitutions and Film‐Formation Process Optimization Enable Approaching 19% Efficiency All‐Polymer Solar Cells

Abstract Molecular interactions and film‐formation processes greatly impact the blend film morphology and device performances of all‐polymer solar cells (all‐PSCs). Molecular structure, such as the central cores of polymer acceptors, would significantly influence this process. Herein, the central core substitutions of polymer acceptors are adjusted and three quinoxaline (Qx)‐fused‐core‐based materials, PQx1, PQx2, and PQx3 are synthesized. The molecular aggregation ability and intermolecular interaction are systematically regulated, which subsequently influence the film‐formation process and determine the resulting blend film morphology. As a result, PQx3, with favorable aggregation ability and moderate interaction with polymer donor PM6, achieves efficient all‐PSCs with a high power conversion efficiency (PCE) of 17.60%, which could be further improved to 18.06% after carefully optimizing device annealing and interface layer. This impressive PCE is one of the highest values for binary all‐PSCs based on the classical polymer donor PM6. PYF‐T‐ o is also involved in promoting light utilization, and the resulting ternary device shows an impressive PCE of 18.82%. In addition, PM6:PQx3‐based devices exhibit high film‐thickness tolerance, superior stability, and considerable potential for large‐scale devices (16.23% in 1 cm 2 device). These results highlight the importance of structure optimization of polymer acceptors and film‐formation process control for obtaining efficient and stable all‐PSCs.