Enantiomerically Pure Fullerenes as a Means to Enhance the Performance of Perovskite Solar Cells

The rapidly advancing improvements in perovskite solar cells (PSCs) are driven, in part, by the inclusion of suitable electron transport layers (ETLs) in high performance devices. Fullerene derivatives are particularly useful ETLs in PSCs, but many of the utilized fullerenes are present as isomeric mixtures. The opportunities presented by single-isomer, single-enantiomer fullerenes in PSCs are poorly understood. Here, inverted PSCs are prepared using bis[60]phenyl-C61-butyric acid methyl ester derivative (anti)16,17-bis[60]PCBM, comparing the performance of enantiomerically pure material to the corresponding racemate. The single enantiomer devices are found to have an improved performance, giving a power conversion efficiency (PCE) of 23.2%, compared to 20.1% PCE for the racemate. It is also shown that enantiomerically pure PSC modules can be prepared with a state-of-the-art PCE of 20.1%. Such excellent performance for the single enantiomer devices is accompanied by enhanced operational stability. This study thus provides strong evidence that single isomer ETLs can provide important improvements in PSC performance and it positions chiral fullerenes as an exciting material class moving forward.