Interfacial Work Function Modulation of Wide Bandgap Perovskite Solar Cell for Efficient Perovskite/CIGS Tandem Solar Cell

Abstract Wide‐bandgap perovskite solar cells (PVSCs), a promising top‐cell candidate for high‐performance tandem solar cells, often suffer from larger open‐circuit voltage ( V OC ) deficits as the bandgap increases. Surface passivation is a common strategy to mitigate these V OC deficits. However, understanding the mechanisms underlying the differences in passivation effects among various types of molecules remains limited, which is crucial for developing universal interface passivation strategies and guiding the design of passivation molecules. This study compares the passivation effects of phenethylammonium iodide (PEAI) and piperazine iodine (PI) on V OC in wide‐bandgap PVSCs with a 1.66 eV bandgap. Results show that PI significantly enhances V OC , whereas PEAI does not. This improvement is attributed to increased built‐in voltage ( V bi ) in PI‐treated PVSCs, stemming from a lower work function, which enhances carrier selectivity at the contact interfaces. The champion power conversion efficiency of the PVSCs is 21.47%, with a V OC of 1.23 V and a V OC loss of 0.43 V. The strategy is also effective for PVSCs with bandgaps of 1.56 and 1.81 eV. By layering semi‐transparent perovskite top cells onto copper indium gallium selenide (CIGS) bottom cells, a PCE of 26.36% is achieved in perovskite/CIGS 4‐terminal tandem solar cells.