As promising candidates for various optoelectronic applications, perovskite-structured materials have attracted tremendous research attention in the scientific community. With the attractive superior virtues involving outstanding carrier mobilities, excellent optical absorption as well as low trap densities, the power conversion efficiency (PCEs) of organicinorganic hybrid halide perovskites (e.g. MAPbI 3 ) solar cells have been boosted from 3.8% to 26.1% over the past decade. The extensive commercialization of hybrid halide perovskites is, however, largely hampered by two key challenges: poor long-term stability and severe toxicity (Pb). The degradation of most hybrid halide perovskites occurs rapidly and irreversibly, due to the intrinsic low formation energy. Substituting the Pb 2+ ion with the less toxic Sn 2+ ion enables materials with similar optoelectronic properties to MAPbI 3 , but encounter even more serious stability issues due to the easy oxidation of Sn 2+ to Sn 4+ .