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 (Eg) value of LiNaPb2Br6 is 1.674 eV at 0 GPa, which is between that of LiPbBr3 and NaPbBr3. Meanwhile, the results indicate that the Eg 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 super- lattices with the application of pressure, the Eg 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 Eg 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.