Electronic structure, mechanical properties and optical properties of three cobalt-based double halide perovskites: A first-principles study

The physical properties of three potential colbat-containing perovskites are studied through first principles calculation. The structural analysis reveals that the Cs2InCoI6 and Cs2AgCoI6 are ductile and potential in flexible devices. The negative formation energies indicate that all these perovskite syntheses are practicable in experiment. However, the results of tolerance factors and phonon spectra are presented against the structural dynamic stability of pure cubic phase of Cs2TlCoI6 and Cs2AgCoI6 and there may be lattice distortion. The band gaps of Cs2InCoI6, Cs2TlCoI6 and Cs2AgCoI6 are 0.833 eV, 1.713 eV and 0.783 eV, respectively, all values are within the ideal range for semiconductors that applied in optoelectronic devices. They all exhibit broad-spectrum light absorption in ultraviolet and visible region, and the absorption coefficient of Cs2InCoI6 even maintains a value above 10000 cm - 1 at wavelength of 1400 nm. Among them, Cs2InCoI6 perovskite has direct band structure, smaller carrier effective mass than that of CsPbI3 and broad solar absorption characteristics, which is considered as a promising candidate material for optoelectronic devices.