Study on the tunable band gap of LiNaPb2Br6 superlattice and its optical properties

The property changes between APbBr₃ (A = Li, Na) and LiPbBr₃/NaPbBr₃ superlattice (LiNaPb₂Br₆), as well as the electronic structure and optical properties of LiNaPb₂Br₆ under various pressures, have been investigated using the GGA-PBE method based on first-principles. The research shows that the band gap (E_g) value of LiNaPb₂Br₆ is 1.674 eV at 0 GPa, which is between that of LiPbBr₃ and NaPbBr₃. Meanwhile, the results indicate that the E_g of LiNaPb₂Br₆ gradually decreases with the increase in pressure, reaching 0.080 eV at 7 GPa, and its valence band top crosses the Fermi level at 8 GPa. Therefore, by combining the construction of superlattices with the application of pressure, the E_g of LiNaPb₂Br₆ can be continuously regulated in the range of 0–1.674 eV. Since the optical properties of a material primarily depend on its band structure, the optical properties of LiNaPb₂Br₆ can be widely adjusted by continuously tuning the E_g of this superlattice. The calculated results demonstrate that the optical properties of LiNaPb₂Br₆ were optimized in comparison to APbBr₃ (A = Li, Na). In addition, the increase in pressure improves the absorption capability of LiNaPb₂Br₆ in both the visible and ultraviolet regions, thereby expanding the potential applications of LiNaPb₂Br₆ in the optical field.