Star-like hexakis[di(ethoxycarbonyl)methano]-C60 with higher electron mobility: An unexpected electron extractor interfaced in photovoltaic perovskites

Abstract Fullerene has been demonstrated to be one of the most efficient electron extractors in perovskite solar cells (PSCs). For feasibly preparing photovoltaic device by solution process, fullerene is normally functionalized in multiple for efficient increase of its solubility in polar solvents. However, multifunctionalization typically results in neighboring fullerene cages alienating to each other and, in principle, reduces electron mobility. Herein, we show a star-like multiadducted fullerene electron extractor, hexakis [di (ethoxycarbonyl)methano]-C60 (HEMC), which possesses a proper solubility in polar solvents as well as a close packing as revealed by crystallography. Likely due to its Th-symmetric structure with twelve ester ‘tentacles’ that can interact with neighboring fullerene derivatives or unsaturated Pb2+ of perovskites, the HEMC displays efficient photovoltaic performances with a power conversion efficiencies of 20%, a storage stability of 3840 h, a thermal stability of 300 h and a light-soaking stability of 240 h in the HEMC-interfaced PSCs. The present work exemplifies an unusual application of fullerene multiadducts, in addition to increasing solubility, for solving charge accumulation and recombination problems in high efficient PSCs.