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

Lead-free CsSnX₃ perovskite NCs are becoming a promising alternative to CsPbX₃ (X=Cl, Br, I), 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 method is proposed for synthesizing CsSnX₃ NCs using Cs₂ CO₃ , SnC₂ O₄ , and NH₄ X as corresponding constituent precursors, wherein the ratio of reactants can be easily adjusted. Stable CsSnX₃ NCs can be obtained with the use of antioxidative SnC₂ O₄ as the Sn^II precursor. Experimental results show that the improvement of NCs stability is mainly ascribed to the role of oxalate in the SnC₂ O₄ 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 shown 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.