The bandgap engineering of double perovskites Cs₂CuSbX₆ (X = Cl, Br, I) for solar cell and thermoelectric applications

Over recent years, the research on lead-free halide double perovskites (DPs)-based materials has credited attention because of their promising applications in solar cells and renewable energy. Herein, we tried to computationally analyze the optoelectronic as well as the thermoelectric characteristics of a unique compound Cs₂CuSbX₆ (X = Cl, Br, I) by density functional theory (DFT). The calculation of tolerance factor (t_F), lattice constant (a_o), and formation enthalpy (ΔH_f) show that the investigated DPs are stable both structurally and thermodynamically. The value of bandgaps of Cs₂CuSbX₆ (X = Cl, Br, I) explicates indirect bandgaps with values 1.04, 0.75, and 0.46 eV for Cs₂CuSbCl₆, Cs₂CuSbBr₆, and Cs₂CuSbI₆, respectively. Further, maximum optical absorption between energy range “1.0 to 3.0 eV” has proved that studied DPs are potential candidates for solar cells and infrared detectors. By exploiting the semi-classical Boltzmann theory, the calculated figure of merit (ZT) verifies the optimal value for electrical conductivity and the respective Seebeck coefficient for the studied compounds. Interestingly, the compound Cs₂CuSbCl₆ has the highest ZT among studied DPs. The present study provides a theoretical base for the studied DPs which is necessary to understand and compare future experimental investigations to seek diverse optoelectronic and thermoelectric applications.