C 60 -based ionic salt electron shuttle for high-performance inverted perovskite solar modules

Although C 60 is usually the electron transport layer (ETL) in inverted perovskite solar cells, its molecular nature of C 60 leads to weak interfaces that lead to non-ideal interfacial electronic and mechanical degradation. Here, we synthesized an ionic salt from C 60 , 4-(1',5′-dihydro-1'-methyl-2' H -[5,6] fullereno-C 60 - I h -[1,9-c]pyrrol-2'-yl) phenylmethanaminium chloride (CPMAC), and used it as the electron shuttle in inverted PSCs. The CH 2 -NH 3 + head group in the CPMA cation improved the ETL interface and the ionic nature enhanced the packing, leading to ~3-fold increase in the interfacial toughness compared to C 60 . Using CPMAC, we obtained ~26% power conversion efficiencies (PCEs) with ~2% degradation after 2,100 hours of 1-sun operation at 65°C. For minimodules (four subcells, 6 centimeters square), we achieved the PCE of ~23% with <9% degradation after 2,200 hours of operation at 55°C.