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, i.e. 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 bandgap 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 linewidths, low trap densities and high room-temperature photoluminance quantum yields, resulting in high-color-purity green 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%.