Ambient Aqueous-Phase Synthesis of Highly Stable Methylammonium Tin Iodide Perovskites Using Alkali Iodides and Ascorbic Acid

Tin iodide perovskites have attracted significant attention as lead-free photoactive layers with excellent optical and electrical properties. A high demand exists for their facile and green synthesis process, not including inert environments and anhydrous organic solvents. In this study, we report a new approach for synthesizing methylammonium tin iodide (MASnI 3 ) perovskites in an ambient aqueous phase. We used lithium iodides or sodium iodides (NaI) as stable solubilizers for tin sources and ascorbic acid (AA) as a safe reductant. Using these reagents, transparent and stable precursor aqueous solutions containing high concentrations of Sn 2+ were successfully prepared, even in ambient air. Mass spectrometry analysis of the precursor aqueous solutions revealed that AA effectively stabilized the Sn 2+ species in the solutions owing to its chelating and reducing abilities. We investigated the degradation process of the MASnI 3 perovskites obtained from these precursor aqueous solutions through structural, chemical, and optical analyses before and after exposure to ambient air. The MASnI 3 perovskites synthesized with NaI and AA exhibited remarkable stability in ambient air. Our results demonstrate that sodium ions and AA present at the surfaces synergistically prevent the oxidative degradation of the MASnI 3 perovskites.