Heteroatom Effect on Star-Shaped Hole-Transporting Materials for Perovskite Solar Cells

Three new star-shaped hole-transporting materials (HTMs) incorporating benzotripyrrole, benzotrifuran, and benzotriselenophene central cores endowed with three-armed triphenylamine moieties (BTP-1, BTF-1, and BTSe-1, respectively) are designed, synthesized, and implemented in perovskite solar cells (PSCs). The impact that the heteroatom-containing central scaffold has on the electrochemical and photophysical properties, as well as on the photovoltaic performance, is systematically investigated and compared with their sulfur-rich analogue (BTT-3). The new HTMs exhibit suitable highest-occupied molecular orbitals (HOMO) levels regarding the valence band of the perovskite, which ensure efficient hole extraction at the perovskite/HTM interface. The molecular structures of BTF-1, BTT-3, and BTSe-1 are fully elucidated by single-crystal X-ray crystallography as toluene solvates. The optimized (FAPbI(3))(0.85)(MAPbBr(3))(0.15)-based perovskite solar cells employing the tailor-made, chalcogenide-based HTMs exhibit remarkable power conversion efficiencies up to 18.5%, which are comparable to the devices based on the benchmark spiro-OMeTAD. PSCs with BTP-1 exhibit a more limited power conversion efficiency of 15.5%, with noticeable hysteresis. This systematic study indicates that chalcogenide-based derivatives are promising HTM candidates to compete efficiently with spiro-OMeTAD.