First-principles study on the mechanical, electronic and optical properties of double halide perovskite Cs2TlSbX6 (X = Cl, Br, I)

The basic physical properties including electronic, mechanical and optical properties of Cs2TlSbX6 (X = Cl, Br, I) are studied by the first principle calculation. The structural stability can be determined by the tolerance factor, formation energy and elastic stability criterion. The results show that these materials are all ductile and suitable for flexible or wearable devices. The direct bandgap values of 1.900eV, 1.583eV and 1.170eV are obtained for Cs2TlSbCl6, Cs2TlSbBr6 and Cs2TlSbI6, respectively, which are in the recommended band gap range of semiconductors with photoelectric applications. Compared with other widely applied perovskite materials, the effective masses of Cs2TlSbX6 (X = Cl, Br, I) materials are smaller, which is beneficial to the carrier transport and helps to improve the performance of optoelectronic devices. In addition, the exploration of optical properties shows that Cs2TlSbX6 (X = Cl, Br, I) perovskites have a promising application in solar cells and other optoelectronic devices.