Phase transformation, morphology control, and luminescence evolution of cesium lead halide nanocrystals in the anion exchange process

Abstract

Colloidal fully inorganic cesium lead halide (CsPbX₃, X = Cl, Br, I) perovskite nanocrystals (NCs) have emerged as next generation candidates for photonics and optoelectronic applications. In this paper, deliberately partial or complete anion exchange reactions in cesium lead halide perovskites have been carried out at room temperature to create homogeneous solid solutions. Through adjusting chemical composition, the photoluminescence properties of the pre-synthesized cesium lead halide perovskite NCs can be tuned to cover the whole visible spectrum through controlling the ratio of parent cesium lead halide NCs and the halide precursors. By exploring the process of anion exchange, it can be concluded that the anion exchange reaction undergoes an inhomogeneous exchange process firstly and the added halide source in the solution is completely exhausted. Finally, the incoming halide will shuttle in the solution phase to reach the steady state and form the homogeneous resulting NCs. When the Br anions in the CsPbBr₃ NCs were replaced by I anions, it is found that the phase composition changed gradually from a cubic to orthorhombic phase with increasing the amount of I anions. It is found that the effective anion exchange process in CsPbX₃ NCs just takes place in the cubic phase rather than others.