The effect of uniaxial strain on electronic and optical properties of halide double perovskites Cs2AgXCl6 (X=Sb, Bi): a DFT approach

The electronic and optical properties for low toxicity, highly stable lead-free halide double perovskites Cs2AgXCl6 (X= Sb, Bi) under the uniaxial strain from −4% to 4% were investigated used by density functional theory. It was found that Cs2AgXCl6 perovskites maintained their indirect band gap under uniaxial strains and the bandgap energies decreased (increased) as the compressive (tensile) strain increased. Both lattice parameters and bond lengths increased (decreased) monotonically with increasing tensile (compressive) strain. The effective mass of electrons (holes) decreased (increased) with the strain from −4% to 4%. Thus, tensile (compressive) strain was more suited to the transport of electrons (holes). The top of the valence band of Cs2AgXCl6 was close to the Fermi energy level and dominated by Cl-3p and Ag-4d orbitals, while the conduction band was dominated by Sb-5p (Bi-6p) and Cl-3p orbitals. The imaginary part ε2(ω) peak intensity decreased with the strain from −4% to 4%. The edges of optical absorption spectra showed blueshift (redshift) under the tensile (compressive). The reflectivity at 0 eV and reflectivity peak in the visible light range decreased (increased) with the increase of tensile (compressive) strain. Therefore, this study provided a theoretical insight into the photoelectronic properties of Cs2AgXCl6 (X= Sb, Bi) under the uniaxial strain. Data are contained within the article and Supplementary materials.