Hydrophilic Fullerene Derivative Doping in Active Layer and Electron Transport Layer for Enhancing Oxygen Stability of Perovskite Solar Cells

Poor stability is one of the main limiting factors for the commercialization of perovskite solar cells (pero‐SCs). The degradation of perovskite films is usually triggered by the reaction of the perovskite active layer with the superoxide when exposed in ambient atmosphere, which is not prevented by simple encapsulation. Herein, an oxygen‐stabilizing effect is found by utilizing a hydrophilic [6,6]‐phenyl‐C 61 ‐butyric acid‐(3,4,5‐tris(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)phenyl)methanol ester (PCBB‐OEG) as a dopant of the perovskite film and electron‐transporting layer (ETL). PCBB‐OEG accelerates photoelectron transport in perovskite films and enhances the electron‐extracting ability of ETL. This process is demonstrated to efficiently prevent the reaction between electrons and oxygen to form a superoxide. Hence, the presence of PCBB‐OEG in the perovskite film improves its stability against oxygen. The stability and efficiency of pero‐SCs are further improved by doping PCBB‐OEG in [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) ETL. As a result, the p‐i‐n pero‐SCs with PCBB‐OEG as an additive in both the perovskite active layer and ETL show the best power conversion efficiency of 20.49%. Importantly, the related device retains 98% of this initial efficiency after 60 days of storage in ambient atmosphere without encapsulation.