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

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.