Mechanically stable X2InAsF6 (X = K, Rb, Cs) for optoelectronic and wasted heat recovery applications.

Herein, the structural, elastic, optoelectronic and thermoelectric properties of double halide X2InAsF6 (X = K, Rb, Cs) perovskites are investigated using density functional theory (DFT). The analysis of structural properties indicates that the studied compounds adopt a stable non-magnetic ground state with Fm3̄m symmetry. The calculated octahedral factor (Δµ), Goldschmidt tolerance factor (τ G), modified tolerance factor (τ), and formation enthalpy (ΔH f) confirm their structural and thermodynamic stability. Mechanical parameters, including Poisson's ratio (ν > 0.26), Pugh's ratio (B/G > 1.75), and the anisotropy factor (A ≠ 1), confirm that all compounds are ductile and elastically anisotropic. The modified Becke Johnson potential (mBJ) calculations reveal direct band gaps of 2.61 eV (K2InAsF6), 2.70 eV (Rb2InAsF6), and 2.74 eV (Cs2InAsF6). Optical analysis reveals strong absorption extending from the visible to ultraviolet regions with high absorption coefficients (α ≈ 104 cm-1) in the 5.9-6.4 eV energy range. Furthermore, the investigated compounds exhibit high Seebeck coefficients (>200 µV K-1) and figures of merit (>0.7) throughout the 300-800 K temperature range. Overall, these findings demonstrate the significant potential of X2InAsF6 compounds for optoelectronic and energy conversion technologies.