Low-LUMO 56π-electron fullerene acceptors bearing electron-withdrawing cyano groups for small-molecule organic solar cells

Abstract

56π-Electron fullerene derivatives with electron-withdrawing cyano groups were synthesized by the reaction of 58π-electron fullerenes with NaCN, followed by in situ treatment with TsCN or MeOTf. The fullerene derivatives have low-lying LUMO levels, which are comparable with or lower than that of pristine C60. They were used as solution-processable electron acceptors in small-molecule organic solar cells that showed a maximum power conversion efficiency of 2.0% (JSC=7.05mA/cm2, VOC=0.62V and FF=0.45) using chloroindium phthalocyanine as an electron donor.