Enhanced Efficiency and Stability of Wide‐Bandgap Perovskite Solar Cells Via Molecular Modification with Piperazinium Salt

Abstract Wide‐bandgap (WBG) perovskite solar cell (PSC) plays a pivotal role as the top subcell in all‐perovskite tandem solar cells (TSCs), facilitating the absorption of high‐energy photons and affording a large open‐circuit voltage ( V OC ). Nonetheless, the stability and efficiency of WBG PSCs are constrained by light‐induced halide segregation and non‐radiative recombination losses. In this study, this work presents an approach of utilizing 2‐methylpiperazinium bromide (2‐MePBr) via interfacial engineering to realize high‐efficiency WBG (1.77 eV) PSCs. The C─NH─C functional group in 2‐MePBr, serving as an electron donor, can interact with under‐coordinated lead defects at the perovskite surface. Consequently, the treatment with 2‐MePBr mitigates interfacial non‐radiative recombination, enhances charge transport, inhibits ion migration, and thus delivers an improved power conversion efficiency (PCE) of 19.30% with a V OC of 1.29 V, and a fill factor of 83.08%. Notably, the WBG PSCs manifest enhanced stability, preserving 80% of the initial PCE after 337 h of continuous operation under 1 sun illumination at the maximum power point. Furthermore, the all‐perovskite TSCs based on this WBG subcell achieve a PCE of 27.47%, showing its promising application in perovskite‐based tandem solar cells.