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 CsPbBr_xCl_3−x, CsPbBr₃, and CsPbBr_xI_3−x are synthesized, and their properties are investigated. Tauc plots calculated from the UV–vis spectra of the materials show that the bandgaps of CsPbBr_xCl_3−x, CsPbBr₃, and CsPbBr_xI_3−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 CsPbBr_xCl_3−x, CsPbBr₃, and CsPbBr_xI_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 CsPbBr_xCl_3−x, CsPbBr₃, and CsPbBr_xI_3−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.