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

Abstract

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 CsPbBrxI3−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.

Fully‐Inorganic Trihalide Perovskite Nanocrystals: A New Research Frontier of Optoelectronic Materials

“…[20] As the halide moves from I (5p 6 ) to Br (4p 6 ) to Cl (3p 6 ), the energies of the halide np 6 orbitals decrease, shifting the VBM toward more positive potentials. [112] As for colloidal CsPbX 3 (X = Cl, Br, and I) NCs, accompanied with changing the composition from CsPbCl 3 to CsPbI 3 through CsPbBr 3 and mixed halides CsPb(Cl,Br) 3 and CsPb(Br,I) 3 , the VBM shifts from −6.24 to −5.44 eV, whereas the CBM shifts from −3.26 to −3.45 eV by means of cyclic voltammetry measurement ( Figure 3b). [112] As for colloidal CsPbX 3 (X = Cl, Br, and I) NCs, accompanied with changing the composition from CsPbCl 3 to CsPbI 3 through CsPbBr 3 and mixed halides CsPb(Cl,Br) 3 and CsPb(Br,I) 3 , the VBM shifts from −6.24 to −5.44 eV, whereas the CBM shifts from −3.26 to −3.45 eV by means of cyclic voltammetry measurement ( Figure 3b).…”

“…[109] The VBM/CBM of CsPbX 3 QDs with compositions of CsPbBr x Cl 3−x , CsPbBr 3 , and CsPbBr x I 3−x (x values are not given in their work) were calculated to be 6.5/3.8, 6.5/4.15, and 6.1/4.3 eV, respectively, from ultraviolet photoemission and UV-vis absorption spectra. [112] As for colloidal CsPbX 3 (X = Cl, Br, and I) NCs, accompanied with changing the composition from CsPbCl 3 to CsPbI 3 through CsPbBr 3 and mixed halides CsPb(Cl,Br) 3 and CsPb(Br,I) 3 , the VBM shifts from −6.24 to −5.44 eV, whereas the CBM shifts from −3.26 to −3.45 eV by means of cyclic voltammetry measurement ( Figure 3b). [109] Hence, a systematic change in the halide compositions of CsPbX 3 NCs from CsPbCl 3 to CsPbBr 3 to CsPbI 3 results in systematic variation in the optical gap from blue to red.…”

All ambient environment-based perovskite film fabrication for photovoltaic applications

“…Cs‐MA, Cs‐FA, and Cs‐FA‐MA have higher crystallinity because these perovskites crystallize at much higher temperature than single‐cation‐based perovskites . Their properties depend upon nature, concentration amount, and temperature as described by Graetzel . An improvement in electronic parameters was observed by Deepa by the incorporation of different concentrations of cesium, which causes improvement in interfacial contacts that ultimately improves device performance by 17%.…”

“…27 Their properties depend upon nature, concentration amount, and temperature as described by Graetzel. 26 An improvement in electronic parameters was observed by Deepa 28 by the incorporation of different concentrations of cesium, which causes improvement in interfacial contacts that ultimately improves device performance by 17%.…”

“…25 In contrast to methylammonium (MA), cesium (Cs), and rubidium (Rb), divalent cation incorporation provides thermodynamically stable phase perovskite solar cells. 26 Cs-MA, Cs-FA, and Cs-FA-MA have higher crystallinity because these perovskites crystallize at much higher temperature than single-cation-based perovskites. 27 Their properties depend upon nature, concentration amount, and temperature as described by Graetzel.…”