Realization of a Highly Oriented MAPbBr₃ Perovskite Thin Film via Ion Exchange for Ultrahigh Color Purity Green Light Emission

Organic–inorganic hybrid perovskites are promising materials for optoelectronic applications. Solution-processed films typically possess deleterious randomly oriented grains that limit their potential. Here, we report growth of highly oriented methylammonium lead bromide (MAPbBr3) films through ion exchange from 2D to 3D perovskite. We first investigate the ion exchange reaction mechanism for conversion between 2D and 3D perovskites using a combined experimental and theoretical approach. The selectivity of conversion is governed by thermodynamics and kinetics of the ion exchange reaction and is intimately linked to the molecular structure of the organic cation in 2D perovskite. Subsequently using the derived insights, we chose phenylethylammonium lead bromide (PEA2PbBr4) as the 2D growth template and successfully exchanged it into high-quality 3D MAPbBr3 films with strong uniaxial 100 orientation. The enhanced film quality leads to ultranarrow electroluminescence spectra (15.3 nm fwhm and 98.10% color purity) and demonstrates the immense potential of the ion exchange method for achieving ultra-high-resolution displays.