Synergistic Solvent and Surface Engineering to Reduce VOC Loss in Tin Halide Perovskite Solar Cells

Tin (Sn) halide perovskites, typically FASnI₃, resemble their lead (Pb)-based counterparts in optoelectronic properties but possess dissimilar crystallization kinetics leading to meager device performance. In this study, we fabricated FASn-halide perovskite solar cells (PSCs) with a high open-circuit voltage (V_OC) of 1042 mV and a power conversion efficiency (PCE) of 15.48%, as verified by an independent photovoltaic lab. By employing a comprehensive solvent and surface engineering strategy, we enhanced crystal stability and grain size, reduced trap state density, and improved energy level alignment. This was achieved by introducing tetraethylammonium (TEA⁺) cation at both surface and bulk grain boundaries, through the post-treatment of perovskite film with a preheated solution mixture of N,N-diethylformamide (DEF) and tetraethylammonium bromide (TEABr) in isopropanol (IPA). This approach also effectively suppressed the notorious Sn²⁺ to Sn⁴⁺ oxidation, resulting in reduced charge carrier trapping at grain boundaries. Moreover, the effectiveness and scalability of this strategy are validated with a 1.02 cm² active area device, achieving a high PCE of 12.21%. Our findings highlight the potential of Sn-halide PSCs to rival Pb-based PSCs in efficiency and stability, paving the way for more environmentally friendly, Pb-free alternatives.