Optoelectronic simulation of a four-terminal all-inorganic CsPbI 3 /CZTSSe tandem solar cell with high power conversion efficiency.

Tandem solar cells based on perovskites have been gaining ever-increasing attention for applications in photovoltaics. Here, we stack the wide-bandgap CsPbI ₃ top subcell with the low-bandgap Kesterite Cu ₂ ZnSnS _x Se _{(4- x )} (CZTSSe) bottom subcell mechanically to form a four-terminal tandem solar cell. The thickness of the CsPbI ₃ and CZTSSe layers, as well as the thickness of ZnO/ZnS and Spiro-OMeTAD layers are optimized to achieve significantly improved absorption, thereby reducing reflection loss and parasitic absorption. The doping concentration on CsPbI ₃ and CZTSSe is investigated to equalize open-circuit voltage and short-circuit current. The energy band-bending and built-in electrical field correlated with carrier separation are discussed. The simulated four-terminal CsPbI ₃ /CZTSSe tandem solar cell affords a summed PCE of 32.35%. The study of the CsPbI ₃ /CZTSSe tandem solar cell provides a promising reference for designing high-performance devices.