Abstract

Atmospheric and mechanical stability of perovskite solar cells (PSCs) must be guaranteed for successful commercialization. A fibrillar polymer, poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT), is reported as an efficient hole transfer layer (HTL) which significantly improves air and mechanical stability of perovskite solar cells (PSCs). PCDTBT fibrils formed at the grain boundaries of perovskite layer induce the highest fracture energies in the PSCs, which provide extrinsic reinforcement and shielding for enhanced mechanical and chemical stability. Debonding energy increases by 30% for the PSCs with PCDTBT fibrils, which fractures at 2.66 J m−2, compared to the devices without PCDTBT fibrils at 2.09 J m−2; more importantly, the threshold debonding driving force of the PCDTBT fibril‐based devices is greatly improved by twofold under ambient conditions.