Enhancing Efficiency and Stability in Organic Photovoltaics through Miscibility of High‐Tg Insulating Material with Y‐Series Nonfullerene Acceptors

Organic solar cells (OSCs) hold significant promise as candidates for next‐generation solar technology. Nevertheless, in state‐of‐the‐art OSCs using Y‐series nonfullerene acceptors, it remains challenging to achieve a high power conversion efficiency (PCE) while simultaneously addressing the inherent thermal instability. This study shows a straightforward additive strategy that can effectively accomplish both goals. By introducing 2 wt% commercially available insulating polyphenylene oxide (SA9000), the PCE and thermal stability of Y6‐based solar cells can be simultaneously improved. Atomic force microscopy confirms a slower coarsening process in the film with SA9000 under thermal stress. The investigation indicates that SA9000's success lies in its excellent miscibility with Y6, which can selectively alter electron mobility, resulting in a balance between hole and electron mobility, and also prevents excessive Y6 aggregation at elevated temperatures. This work reveals a selection criterion for commercial and low‐cost insulating materials as an additive to effectively improve the performance and stability of OSCs simultaneously.