Prediction of X2AuYZ6 (X = Cs, Rb; Z = Cl, Br, I) double halide perovskites for photovoltaic and wasted heat management device applications

We used density functional theory to study the phase stability, the opto-electronic properties, and the thermoelectric behavior of X(2)AuYZ(6) (where X = Cs, Rb, and Z = Cl/Br/I) double halide perovskites. The compounds belong to the cubic perovskite arrangement and are verified by the tolerance and octahedral factor. Formation enthalpy and binding energy primarily meet the requirements for structural stability. The positive frequency of phonon dispersion shows that all compounds are dynamically stable except for Rb2AuYI6. The negative formation energy considering the competing phase also confirmed that all compounds are thermodynamically stable. The Pugh's ratio, Poisson's ratio, and Cauchy pressure validated their ductile nature in the analysis of thermomechanical behavior. The electronic characteristics of Cs(2)AuYZ(6) (Rb(2)AuYZ(6)) [Z = Cl, Br, I] double halide perovskites (DHP) have been investigated using the TB-mBJ technique, yielding band gap values of 2.85 (2.91), 2.35 (2.40), and 1.74 (1.78) eV, in that order. The optical properties are calculated, revealing the maximum absorption coefficients with respect to wavelength in the visible range of the titled compounds are 0.23 (0.35) x 10(5) cm(-1), 1.01 (1.06) x 10(5) cm(-1), and 1.42 (1.48) x 10(5) cm(-1), respectively, indicating their potential for photovoltaic applications. The thermo-electric transport properties were also studied. The investigated compounds [Cs (Rb)-based] exhibit ZT values of 0.51 (0.55), 0.53 (0.62), and 0.58 (0.75) at room temperature with Cl, Br, and I, respectively. As a result, the studied compounds, particularly those Rb-based with halides, have significantly greater potential than Cs in thermoelectric fields. So, among the compounds, X2AuYI6 (X = Cs, Rb) shows the most promise for the technological applications mentioned above due to its lower band gap, high absorption coefficient, and high ZT value.