Single enantiomer chiral fullerenes enable interfacial toughening of perovskite solar cells

The rapid advancements in perovskite solar cell (PSC) technologies are partly fueled by the integration of suitable electron transport layers (ETLs) to boost device performance. Despite continued improvements, inadequate robustness of the interface between the ETL and the perovskite limits PSC performance and operational stability. Fullerene derivatives are excellent ETLs in PSCs, though many commonly used fullerenes are used as mixtures of different isomers. The potential advantages of using single-isomer, single-enantiomer fullerenes in PSCs are poorly explored. In this study, we compare inverted PSCs incorporating the enantiomerically pure bis[60]phenyl-C₆₁-butyric acid methyl ester derivative (R,S, ^f,sA)49,59-bis[60]PCBM (trans-2) with a comparator enantiomer and with racemic material. Devices using this particular enantiomer exhibit significantly enhanced performance, achieving a power conversion efficiency (PCE) of 24.3%, as well as significantly enhanced ambient, thermal and operational stability. Overall, this study further highlights the promising role of single-isomer ETLs in advancing PSC technologies and provides early design rules of high-performance chiral fullerenes to enable future developments.