Conductive fullerene surfactants via anion doping as cathode interlayers for efficient organic and perovskite solar cells

Conductive fullerene surfactants, FPPI, Bis-FPPI, Bis-FIMG and Bis-FITG, are developed as electron transporting materials for achieving efficient organic and perovskite solar cells (OSCs and PVSCs) under mild solution-fabrication. One common structural feature of these fullerenes is a quaternary ammonium halide moiety, which enables electron transfer from constituent Lewis basic halides to adjacent π-acidic fullerene, resulting in anion-induced n-doping of the derived fullerenes. These polar fullerenes, herein with suitable conductivities, work-function tunability and orthogonal solution-process abilities (to common organic semiconductors and perovskites), possess advantages as interlayers not only enabling good photovoltaic performance of OSCs and PVSCs, with over 19% power conversion efficiency made from mild fabrication, but also showing device performance insensitive to the interlayer thickness.