α-DTC70 fullerene performs significantly better than β-DTC70 as electron transporting material in perovskite solar cells

In this work, two new C-70 isomers, alpha and beta bis(2-(thiophen-2-yl)ethyl)-C-70-fullerene mono-adducts (DTC70), were synthesized, characterized and used as electron transporting materials (ETMs) in perovskite solar cells (PSCs). Our results show that the alpha isomer improves both the J(sc) and FF values of the devices, when compared to the results for the beta-isomer and to those for phenyl-C-70-butyric acid methyl ester (PC71BM), used as control. Devices based on alpha-DTC70 achieved a power conversion efficiency (PCE) of 15.9%, which is higher than that observed with PC71BM (15.1%).