ZnX2 mediated post-synthetic transformation of zero dimensional Cs4PbBr6 nanocrystals for opto-electronic applications

Abstract

Herein we demonstrate a facile approach for the synthesis of all inorganic cesium lead halide perovskite nanocrystal composites CsPbX₃ (X = Cl, Br, I) with high quantum yield by post-synthetic modulation of zero dimensional Cs₄PbBr₆ nanocrystals with ZnX₂ salts. The transformation of Cs₄PbBr₆ nanocrystals into CsPbBr₃ takes place in two steps, the first step being the surface modification of the Cs₄PbBr₆ nanocrystals with Zn²⁺ ions and the second step being extraction of CsBr by the Zn²⁺ ions resulting in the formation of composite Cs₄PbBr₆/CsPbBr₃ nanocrystals. The transformed composite nanocrystals were found to have a PL QY exceeding 90% and the shape of the nanocrystals also changed from hexagonal to cubic shaped. Owing to the highly ionic nature of the nanocrystals, complete anion exchange could be also realized using ZnI₂ salt. In the case of the iodide post-treated samples, nanorods were obtained which exhibited bright red photoluminescence. Photodetectors based on the ZnI₂ treated Cs₄PbBr₆ NCs were fabricated, and the photodetectors exhibited a high on/off ratio with a fast response time. The excellent optoelectronic properties make this treatment versatile for a wide range of functional optoelectronic devices like light emitting diodes and photovoltaic devices.