An anion-driven Sn2+ exchange reaction in CsPbBr3 nanocrystals towards tunable and high photoluminescence

Abstract

Fast and efficient ion-exchange reactions endow CsPbX₃ nanocrystals (NCs) with superior photoluminescence (PL) properties. In this study, SnX₂ (X = I, Cl) was used as a Sn precursor to conduct the cation exchange reaction, which was promoted by anion exchange between the parent CsPbBr₃ NCs and the guest X in SnX₂. The anion-driven cation exchange reaction occurred efficiently (10 min). CsSnI₃ NCs were created by ion-exchange reactions between CsPbBr₃ NCs and the SnI₂ precursor. The CsSnI₃ NCs retained the initial morphology of CsPbBr₃ NCs and revealed a high PL efficiency (59%) and prolonged PL lifetime. In contrast, the exchange reaction of Sn²⁺ ions in CsPbBr₃ NCs did not occur in a short time using SnBr₂ as a precursor. After the cation exchange reaction, the 4f peaks of Pb ions in X-ray photoelectron spectroscopy spectra shifted to low binding energies as compared to those of the parent CsPbX₃ NCs. This is ascribed to the increase in the number of Pb–oleate (Pb–OA) species. Contrary to the hot-injection method used to synthesize CsSnI₃ NCs, the kinetically controlled ion exchange reactions lead to the synthesis of CsSnI₃ NCs with a high structural stability. Thus, an anion-exchange-promoted cation exchange reaction is a particularly efficient versatile tool to dope Sn²⁺ into CsPbX₃ NCs.