Integrated 4-Terminal All-Inorganic Perovskite Tandem Solar Cell with Open-Circuit Voltage Exceeding 2.1 V for Water Splitting

This work reports on Sn-Pb binary metal inorganic perovskites as narrow-bandgap absorbers for integrated 4-terminal all-inorganic perovskite tandem solar cells (TSCs). A series of Sn-Pb binary metal CsPb1–xSnxI3-yBry inorganic perovskites with tunable bandgaps ranging from 1.28 to 1.45 eV were synthesized through tuning the Sn-Pb and I-Br contents. The TSC device using a narrow-bandgap CsPb0.5Sn0.5I2.7Br0.3 bottom cell with a wide-bandgap semi-transparent CsPbI1.5Br1.5 top cell achieved a remarkable power conversion efficiency over 18% and a high open-circuit voltage (VOC) of 2.13 V, a very attractive feature for solar fuel production. To the best of our knowledge, this is the first trial of TSCs entirely made of all-inorganic perovskite absorbers, and also the record VOC achieved among double-junction TSCs based on integration of narrow- and wide-bandgap perovskite absorbers so far. Using this novel all-inorganic perovskite TSC in conjunction with a water-splitting system employing Pt/C for hydrogen evolution reaction and Fe/Ni foam for oxygen evolution reaction in alkaline electrolyte, we achieved an unprecedented solar-to-hydrogen efficiency over 13% under standard illumination test conditions.