Ultra-Halide-Rich Synthesis of Stable Pure Tin-Based Halide Perovskite Quantum Dots: Implications for Photovoltaics

Tin (Sn)-based halide perovskites crystallized in the form of quantum dots (QDs) have attracted considerable attention due to their attractive features that are unique to the quantum realm. However, unlike those of their lead (Pb) counterparts, isolation and purification of the as-synthesized Sn-based QDs remain a challenge, as they undergo rapid decomposition in the most common antisolvents as well as in open air. Herein, we discover that CsSnX3 (X = Cl, Br, and I) QDs prepared under ultra-halide-rich conditions exhibit superior durability against the antisolvents even with high hydrophilicity like methyl acetate and can be thus readily purified under ambient conditions without the need for a strict inert atmosphere. First principles calculations reveal that halide-rich synthesis favors the formation of enhanced chemical bonds between QDs and their surface ligands and reduces ligand mobility. Both help to prevent structural decomposition and to preserve the perovskite composition. The successful synthesis of structurally stable Sn-based perovskite QDs accomplished without the use of any particular antioxidants or additional doping, provides alternative material design strategies for enhancing the stability of these fascinating yet fragile nanomaterials.