Interfacial Engineering of Wide‐Bandgap Perovskites for Efficient Perovskite/CZTSSe Tandem Solar Cells

Abstract Wide‐bandgap perovskites have attracted substantial attention due to their important role in serving as a top absorber in tandem solar cells (TSCs). However, wide‐bandgap perovskite solar cells (PVSCs) typically suffer from severe non‐radiative recombination loss and therefore exhibit high open‐circuit voltage ( V OC ) deficits. To address these issues, a 2D octyl‐diammonium lead iodide interlayer is adopted onto the hole‐transporting layer to induce the formation of an ultrathin quasi‐2D perovskite that is close to the hole‐selective interface. This approach not only accelerates hole transfer and retards hole accumulation but also reduces the trap density in the perovskite layer on top, thereby efficiently suppresses non‐radiative recombination pathways. Consequently, the champion wide‐bandgap device (≈1.66 eV) exhibits a power conversion efficiency (PCE) of 21.05% with a V OC of 1.23 V, where the V OC deficit of 0.43 V is among the lowest values for inverted wide‐bandgap PVSCs. Moreover, by stacking a semi‐transparent perovskite top cell on a 1.1 eV Cu 2 ZnSn(S,Se) 4 (CZTSSe) bottom cell, a 22.27% PCE was achieved on a perovskite/CZTSSe four‐terminal tandem solar cell, paving the way for all‐solution‐processed, low‐cost, and efficient TSCs with mitigated energy loss in the wide‐bandgap top cells.