Investigating the physical properties of lead-free halide double perovskites Cs2AgXBr6 (X = P, As, Sb) for photovoltaic and thermoelectric devices using the density functional theory

Abstract

Lead-free halide double perovskites are promising materials for photovoltaic and thermoelectric applications due to their desirable functional features. In the present study, Wien2k ab-initio code based on the density functional theory (DFT) was employed to Cs2AgXBr6 (X = P, As, and Sb) to investigate their structural, electronic, mechanical, optical, and thermoelectric properties. The obtained results show that all compounds are mechanically stable. Both Cs2AgPBr6 and Cs2AgSbBr6 are ductile materials whereas Cs2AgAsBr6 is brittle. On the other hand, the atomic bonds of Cs2AgAsBr6 are stronger than those of the other two compounds, and its lattice structure is more rigid. Based on the hybrid functional (YS-PBE0) potential, the bandgap of Cs2AgXBr6 (X = P, As and Sb) was identified as indirect and have the values of 1.113, 1.517, and 1.672 eV, respectively. All compounds have high optical conductivity in the visible region and show the greatest absorption in the UV–visible region. Additionally, the positive values of Seebeck and Hall coefficients over the entire temperature range indicate the presence of hole-type charge carriers in these materials. The calculated thermoelectric Figure of Merit shows a broad plateau over the investigated temperature range which ensures stable efficiency over a wide operating temperature range. The present study demonstrates the potential of the investigated compounds to be utilized in photovoltaic and thermoelectric applications.