Cesium Methylammonium Lead Iodide (Cs_<i>x</i>MA_1−<i>x</i>PbI₃) Nanocrystals with Wide Range Cation Composition Tuning and Enhanced Thermal Stability of the Perovskite Phase

Abstract

Cesium methylammonium lead iodide (Cs_x MA_1-x PbI₃ ) nanocrystals were obtained with a wide range of A-site Cs-MA compositions by post-synthetic, room temperature cation exchange between CsPbI₃ nanocrystals and MAPbI₃ nanocrystals. The alloyed Cs_x MA_1-x PbI₃ nanocrystals retain their photoactive perovskite phase with incorporated Cs content, x, as high as 0.74 and the expected composition-tunable photoluminescence (PL). Excess methylammonium oleate from the reaction mixture in the MAPbI₃ nanocrystal dispersions was necessary to obtain fast Cs-MA cation exchange. The phase transformation and degradation kinetics of films of Cs_x MA_1-x PbI₃ nanocrystals were measured and modeled using an Avrami expression. The transformation kinetics were significantly slower than those of the parent CsPbI₃ and MAPbI₃ nanocrystals, with Avrami rate constants, k, at least an order of magnitude smaller. These results affirm that A-site cation alloying is a promising strategy for stabilizing iodide-based perovskites.