Probing the opto-electronic, phonon spectrum, and thermoelectric properties of lead-free fluoride perovskites AGeSnF (A = K, Rb, Cs) for energy harvesting devices.

The present work employs density functional theory to explore the structural, optoelectronic, and thermoelectric attributes of the halide-based double perovskite AGeSnF (A = K, Rb, and Cs) compounds. The stable phonon dispersion spectrum affirms dynamical stability, whereas the enthalpy of formation and tolerance factor evaluated collectively verify structural stability. Considering the Tran Blaha modified Becke Johnson potentials (mBJ), the predicted direct band gaps along the symmetry point are 3.19 eV for KGeSnF, 3.16 eV for RbGeSnF and 3.12 eV CsGeSnF. According to an in-depth examination of the optoelectronic features, AGeSnF (A = K, Rb, and Cs), double perovskites are assuring contenders for optoelectronic devices due to their suitable bandgap. The extremely high figure of merit values (0.94-0.97) obtained from the numerical calculation of power factor and thermal conductivity suggest the intriguing prospects of these compositions for thermoelectric devices. These studies offer a perceptive comprehension of the materials for their potential applications in the future.