Indene-C₆₀ Bisadduct Electron-Transporting Material with the High LUMO Level Enhances Open-Circuit Voltage and Efficiency of Tin-Based Perovskite Solar Cells

Tin-based halide perovskite materials are promising ecofriendly light absorbers with similar optoelectronic properties to lead-based ones. However, their solar cells have suffered from considerably low open-circuit voltage (VOC) arising from mismatched energy levels between tin-based perovskite and charge-transporting layers because they imitate typical device structures developed for lead-based ones. Herein, we report that the lowest unoccupied molecular orbital (LUMO) level of the electron-transporting layer (ETL) significantly affects VOC of tin-based perovskite solar cells (PSCs) in contrast to lead-based ones. The indene-C60 bisadduct ETL with a much higher LUMO level than that of typical ETLs decreases an energy off-set with the conduction band minimum of the mixed formamidinium/phenylethylammonium tin iodide (FA0.9PEA0.1SnI3)-based perovskite material. The resultant reduced VOC loss at their interface gives a VOC of 0.651 V, the highest to date for FASnI3-based PSCs. The achieved champion power conversion efficiency reaches 7.05%. This result highlights the importance of redesigning device structures dedicated to tin-based PSCs.