Boosting Perovskite Solar Cells Efficiency and Stability: Interfacial Passivation of Crosslinked Fullerene Eliminates the “Burn‐in” Decay

Abstract Perovskite solar cells (PSCs) longevity is nowadays the bottleneck for their full commercial exploitation. Although lot of research is ongoing, the initial decay of the output power – an effect known as “burn‐in” degradation happening in the first 100 h – is still unavoidable, significantly reducing the overall performance (typically of >20%). In this paper, the origin of the “burn‐in” degradation in n‐i‐p type PSCs is demonstrated that is directly related to Li+ ions migration coming from the SnO2 electron transporting layer visualized by time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) measurements. To block the ion movement, a thin cross‐linked [6,6]‐phenyl‐C61‐butyric acid methyl ester layer on top of the SnO2 layer is introduced, resulting in Li+ immobilization. This results in the elimination of the “burn‐in” degradation, showing for the first time a zero “burn‐in” loss in the performances while boosting device power conversion efficiency to >22% for triple‐cation‐based PSCs and >24% for formamidinium‐based (FAPbI3) PSCs, proving the general validity of this approach and creating a new framework for the realization of stable PSCs devices.