Cesium Methylammonium Lead Iodide (CsxMA1−xPbI3) 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 PbI 3 ) nanocrystals were obtained with a wide range of A‐site Cs‐MA compositions by post‐synthetic, room temperature cation exchange between CsPbI 3 nanocrystals and MAPbI 3 nanocrystals. The alloyed Cs x MA 1− x PbI 3 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 MAPbI 3 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 PbI 3 nanocrystals were measured and modeled using an Avrami expression. The transformation kinetics were significantly slower than those of the parent CsPbI 3 and MAPbI 3 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.