Improvement of Photophysical Properties of CsPbBr$_3$ and Mn$^{2+}$:CsPb(Br,Cl)$_3$ Perovskite Nanocrystals by Sr$^{2+}$ Doping and Their Application in White-LEDs

All-inorganic lead halide perovskite nanocrystals (NCs) show potential in optoelectronic devices, though their stability and efficiency have yet to improve. In this work, we explore the effect of bivalent metal site doping on the optoelectronic properties of CsPbX$_3$ (X = Br, Cl) perovskite NCs. First, the Pb$^{2+}$ ions in pristine CsPbBr$_3$ NC are partially substituted by Mn$^{2+}$ ions, and the alkaline earth metal strontium is then doped on both pristine and Mn$^{2+}$-substituted particles. The structural and photophysical properties of the pristine and the three doped NC variants have been investigated experimentally as well as exploiting first principles calculations. We found that a small percentage of Sr$^{2+}$-doping improved the photoluminescence quantum yield of the pristine particle by 8%, while it improved the Mn$^{2+}$-state emission by 7%. Perovskite NC film/poly(methyl methacrylate) composites with all four NC variants were used in a white light-emitting diode (WLED) and again both Sr$^{2+}$ doped NCs were found to increase the luminous efficiency of the WLED by ca 4 %. We attribute this performance enhancement to a reduced defect density as well as an attenuated microstrain in the local NC structure.