In this work, the structural, mechanical, optoelectronic and thermoelectric properties of K₂AgXI₆ (X = Sb, Bi) double perovskite materials are investigated using Density Functional Theory (DFT) as implemented in WIEN2k code both at ambient and under different hydrostatic pressure ranging up to 20 GPa for K₂AgSbI₆ and up to 50 GPa for K₂AgBiI₆. The structural stability of the compounds are ensured by the Goldschmidt tolerance factor (τ) and the octahedral factor (µ). Our studied compounds exhibit perfectly cubic structures with the space group Fm3̄m (space group no. 225). The band structure shows p-type semiconducting nature with an indirect band gap of 0.97 eV for K₂AgSbI₆ and 1.599 eV for K₂AgBiI₆ at ambient condition and band gap gradually decreases with induced pressure. Optical analysis shows that the highest transition occurs in the visible spectrum after increasing pressure for both systems compared to ambient conditions. Therefore, the studied compounds under investigation may be suitable for solar cell applications. The transport properties of both materials are investigated using the BoltzTraP code to estimate the electrical and thermal conductivities, Seeback coefficient, power factor, and figure of merit under different hydrostatic pressures. The high values of the Seebeck coefficient and the figure of merit ensure that the studied compounds are suitable for thermoelectric applications at ambient conditions rather than under pressurized conditions. Finally, our studied compounds demonstrate good mechanical stability under applied pressure, indicating that pressure has a significant impact on their mechanical resilience.

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