Stable and Efficient Tin-Based Perovskite Solar Cell via Semiconducting–Insulating Structure

Tin halide perovskite solar cells (PSCs) have attracted great attention in very recent years due to their low toxicity, suitable band gap, and high light absorption coefficient. However, the power conversion efficiency (PCE) and stability of Sn-based PSCs are still much lower than that of their lead-based counterparts. The main reason comes from the Sn2+ ions spontaneously oxidizing into Sn4+ under ambient air conditions. The resulting self-p-type doping of the Sn-based perovskite layer becomes unsuitable and leads to poor photovoltaic performance. Herein, we demonstrate the fabrication of a semiconducting–insulating interface fully covering the formamidinium tin iodide (FASnI3) with a thin layer of poly(methyl methacrylate) (PMMA). The PMMA layer does not only protect FASnI3 from oxygen and moisture but also effectively passivate defect-driven recombination, resulting in improved open-circuit voltage. As a result, devices using a PMMA-FASnI3 layer exhibit a much higher PCE (10.8%) and better stability compared to devices based on pristine FASnI3 (7.7%). Importantly, the PMMA-FASnI3 devices maintain about 80% of their initial efficiency after being stored for 240 h under ambient conditions (25 °C, 60 RH%) without requiring any further encapsulation.