Dual-site vacancy filling strategy enhances efficiency and stability of tin-based perovskite solar cells

Tin-based perovskite solar cells (TPSCs) have garnered considerable attention due to their favorable optoelectronic properties and environmental compatibility. However, during the fabrication of tin perovskite films, defects inevitably occur, inducing non-radiative recombination and accelerating film degradation. Here, we introduce a novel dual-site vacancy filling strategy by inducing the pyrrolidine hydroiodide (PyI) as an additive into the precursor. In the perovskite lattice, Py⁺ and I^- ions from PyI selectively occupy A-site and X-site vacancies of tin perovskite, respectively, leading to a significant reduction in both positively and negatively charged defects. This strategy effectively reduces the defects and suppresses non-radiative recombination. Besides, the incorporation of PyI results in deeper valence and conduction band positions in the active layer, leading to improved energy level alignment with the adjacent transport layers. As a result, the best-performing TPSC achieves a power conversion efficiency (PCE) of 11.43 %, and maintains 86 % of its initial efficiency after 1100 h of storage in N₂ with an oxygen concentration of 50-100 ppm. The dual-site vacancy filling strategy holds significant promise for lead-free perovskite photovoltaics by effectively mitigating defect-induced non-radiative recombination and enhancing both device efficiency and long-term stability.