Synergistic Defect Passivation with Enhanced Light and Thermal Resilience for p-i-n CsFA-Based Perovskite Solar Cells

Effective passivation of bulk and interface defects is one of the key drivers for achieving highly efficient and stable p-i-n perovskite solar cells (PSCs). Despite the versatility of bulky ammonium cations in defect passivation, ionic migration of these cations under light and thermal stresses is undesirable for maintaining the integrity of the passivation layer and thus detrimental to the device performance and long-term stability. To address this issue, a stepwise passivation approach employing 2-methoxyphenylethylammonium (2-MeO-PEA+) cation and piperazine dihydroiodide (PipDI) is proposed. By integrating bulk incorporation and subsequent surface treatment, the passivation approach synergistically mitigates both bulk and interface defects, and thereby enhances the resilience of the perovskite layer against light and thermal stresses. Owing to the significantly improved morphology, crystallinity, and optoelectronic properties of the perovskite layer, a champion PSC device with a PCE of 26.10% and outstanding stability is achieved, demonstrating the feasibility of the proposed two-step passivation approach.