First-principles calculations to investigate lead-free double perovskites CsInSbAgX6 (X = Cl, Br and I) for optoelectronic and thermoelectric applications

In this study, novel lead-free double perovskites CsInSbAgX6 (X = Cl, Br and I) are proposed and theoretically investigated for the first time for their potential application in optoelectronic and thermoelectric devices. Density Functional Theory was applied to study their physical properties. The results showed that the materials are chemically and mechanically stable as well as ductile. The materials possess indirect (X-L) semiconducting behavior with band gaps: 1.37 eV, 0.86 eV, and 0.46 eV using GGA functional while improved band gaps using hybrid HSE functional were 1.44 eV, 0.95 eV, and 0.54 eV, for the respective compounds. Moreover, the compounds are observed to have high absorption and low reflectivity in UV region while CsInSbAgI6 is also predicted to absorb visible light and hence suitable for optoelectronic applications. Finally, results also show that the materials have high electrical and thermal conductivity and that they are predicted to have the best thermoelectric performance at 800 K.