Efficient and High-Color-Purity Light-Emitting Diodes Based on In Situ Grown Films of CsPbX₃ (X = Br, I) Nanoplates with Controlled Thicknesses

We report a facile solution-based approach to the in situ growth of perovskite films consisting of monolayers of CsPbBr₃ nanoplates passivated by bulky phenylbutylammonium (PBA) cations, that is, two-dimensional layered PBA₂(CsPbBr₃)_n-1PbBr₄ perovskites. Optimizing film formation processes leads to layered perovskites with controlled n values in the range of 12-16. The layered perovskite emitters show quantum-confined band gap energies with a narrow distribution, suggesting the formation of thickness-controlled quantum-well (TCQW) structures. The TCQW CsPbBr₃ films exhibit smooth surface features, narrow emission line widths, low trap densities, and high room-temperature photoluminance quantum yields, resulting in high-color-purity green light-emitting diodes (LEDs) with remarkably high external quantum efficiencies (EQEs) of up to 10.4%. The solution-based approach is extended to the preparation of TCQW CsPbI₃ films for high-color-purity red perovskite LEDs with high EQEs of up to 7.3%.