Tuning Mechanism of Optical Bandgap in CsPbBrxCl3-x Single-Crystal Microplatelets via Halide Hybridization

Halide hybridization in CsPbX3 perovskite is one of the most popular methods to precisely tune its optical bandgap for covering a wider wavelength range. However, the halide hybridization mechanism and the intrinsic structure-property correlation of hybrid CsPbX3 require deep exploration. Therefore, CsPbBrxCl3-x single-crystal microplates have been synthesized using CVD method and the evolution of structure and luminescent properties have been revealed systematically using the spectroscopic techniques, such as microfocused Raman and PL. The results demonstrate that as the Br element in CsPbBrxCl3-x microplates increases, the tetragonal crystal structure is always kept, the PL emission wavelength and Raman shifts can be finely and regularly tuned. It is proposed that the precise tuning of bandgap attributes to the length average of Cl(Br)-Pb bonds, the nature of halide hybridization is the formation of distorted hybrid PbBrxCl6-x4- octahedral structure through substitution of some Cl- by Br- in CsPbCl3 lattice. Consequently, the optical bandgap of CsPbBrxCl3-x is effectively modulated by the upward shift of the VBM and the slight downward shift of the CBM. These studies provide essential evidences for understanding the nature of bandgap modulation in hybrid CsPbBrxCl3-x perovskite and are expected to facilitate the development of advanced optoelectronic devices.