Identification of lead-free double halide perovskites for promising photovoltaic applications: first-principles calculations

The first-principles calculation has been carried out for the investigation of electronics, structural, and optical properties of A(2)MM ' X-6 by tight binding approaches. Among 30 combinations, only six systems, namely Rb2AgInBr6, Cs2AgInBr6, Cs2InBiCl6, Rb2TlAsBr6, Cs2TlAsBr6, and Cs2TlSbBr6, are found to be suitable for solar cell applications because of their suitable electronic properties. In addition, the obtained negative formation energy of Rb2AgInBr6, Cs2AgInBr6, Cs2InBiCl6, Rb2TlAsBr6, Cs2TlAsBr6, Cs2TlSbBr6 confirmed their thermodynamic stability. Moreover, the lack of imaginary frequency in phonon dispersion band structure implies that their cubic structure is stable against lattice distortion. Moreover, the obtained lower R (%) with higher values alpha and sigma revealed that they are suitable for solar cell applications. The detailed optical analyses revealed that the Rb2TlAsBr6 has the highest alpha and sigma in the entire visible energy range indicating that it is the most promising material.