Improvement of Photophysical Properties of CsPbBr₃ and Mn²⁺:CsPb(Br,Cl)₃ Perovskite Nanocrystals by Sr²⁺ Doping for White Light-Emitting Diodes

All-inorganic metal halide perovskite nanocrystals (NCs) having the general formula ABX₃, where A is a monovalent cation, for example, Cs⁺, B is a divalent cation, typically Pb²⁺, and X is Cl^–, Br^–, I^–, or their binary mixture, show potential in optoelectronic devices. In this work, we explore the effect of B-site doping on the optoelectronic properties of CsPbX₃ NCs (X = Br, Cl). First, the Pb²⁺ ions in the pristine CsPbBr₃ NC are partially substituted by Mn²⁺ ions. The alkaline earth metal strontium is then doped on both pristine and the Mn²⁺-substituted NCs. We found that a small percentage of Sr²⁺ doping remarkably improves the photoluminescence quantum yield of CsPbBr₃ and Mn²⁺-state emission in Mn²⁺:CsPb­(Br,Cl)₃ NCs. Perovskite NC film/poly­(methyl methacrylate) composites with all four NC variants were used in a white light-emitting diode (WLED), where Sr²⁺ doping increased the luminous efficiency of the WLED by ∼4.7%. We attribute this performance enhancement to a reduced defect density and an attenuated microstrain in the local NC structure.