Enhanced Open-Circuit Voltage in Perovskite Solar Cells with Open-Cage [60]Fullerene Derivatives as Electron-Transporting Materials

The synthesis, characterization, and incorporation of open-cage [60]fullerene derivatives as electron-transporting materials (ETMs) in perovskite solar cells (PSCs) with an inverted planar (p-i-n) structure is reported. Following optical and electrochemical characterization of the open-cage fullerenes 2a–c, p-i-n PSCs with a indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS)/perovskite/fullerene/Ag structure were prepared. The devices obtained from 2a–b exhibit competitive power conversion efficiencies (PCEs) and improved open-circuit voltage (V(oc)) values (>1.0 V) in comparison to a reference cell based on phenyl-C(61)-butyric-acid methyl-ester (PC(61)BM). These results are rationalized in terms of a) the higher passivation ability of the open-cage fullerenes with respect to the other fullerenes, and b) a good overlap between the highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) levels of 2a–b and the conduction band of the perovskite.