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

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.