Investigation of Energy Levels and Crystal Structures of Cesium Lead Halides and Their Application in Full-Color Light-Emitting Diodes

Inorganic CsPbX3 perovskites with compositions including CsPbBrxCl3-x,CsPbBr3, and CsPbBrxI3-x are synthesized, and their properties are investigated. Tauc plots calculated from the UV-vis spectra of the materials show that the bandgaps of CsPbBrxCl3-x, CsPbBr3, and CsPbBrxI3-x are 2.7, 2.35, and 1.8 eV, respectively. The as-prepared CsPbX3 nanodots have a cubic structure and their crystal sizes are around 5-10 nm. The diffraction peak intensity of the (110) plane is increased by adding Cl anion and reduced by adding I anion. By contrast, the peak intensity of the (200) plane is reduced by the introduction of Cl-ions and increased by the introduction of I-ions, suggesting that the nature of the halide anions affects the crystal orientation of CsPbX3 quantum dots. The highest occupied molecular orbital/lowest unoccupied molecular orbital levels of CsPbBrxCl3-x, CsPbBr3, and CsPbBrxI(3-x) calculated from ultraviolet photoemission spectra and UV-vis spectra are 6.5/3.8, 6.5/4.15, and 6.1/4.3 eV, respectively. The maximum luminance values measured for CsPbBrxCl3-x, CsPbBr3, and CsPbBrxI3-x-based light-emitting diodes (LEDs) are 15.2, 51.7, and 21.7 cd m(-2), respectively. This research provides an overview of the energy levels and crystal structures of CsPbX3 quantum dots for the design of inorganic perovskite-based LEDs with high luminance and power efficiencies.