Antioxidative Stannous Oxalate Derived Lead-Free Stable CsSnX3 (X = Cl, Br, and I) Perovskite Nanocrystals.

The current research on all-inorganic perovskite NCs is mainly focused on Pb-based materials (CsPbX3, X = Cl, Br, and I). However, the toxicity of Pb has become a major obstacle to its application. Correspondingly, lead-free CsSnX3 perovskite NCs are becoming a promising alternative, but suffer from extremely poor stability. Herein, we highlight the significant effect of Sn(II) precursors used in the synthesis on the stability of the resultant CsSnX3 NCs. A new method is proposed for synthesizing CsSnX3 NCs using Cs2CO3, SnC2O4, and NH4X as corresponding constituent precursors, wherein the ratio of reactants can be facilely adjusted. Stable CsSnX3 NCs can be obtained with the use of antioxidative SnC2O4 as the Sn(II) precursor. Experimental results show that the improvement of NCs stability is mainly ascribed to the role of oxalate in the SnC2O4 precursor. Oxalate ion has a strong antioxidative ability and can effectively inhibit the oxidation of Sn(II) during the synthesis. Besides, oxalate as a bidentate capping ligand is demonstrated to be coordinated on the surface of formed NCs. This can not only passivate the uncoordinated Sn on the surface but also prevent the oxidation of the NCs.