The development of lead-free halide double perovskites for renewable energy is an emerging field due to their interesting properties, such as high efficiency in light absorption, excellent stability under various environmental conditions, and potential for cost-effective large-scale production. In this work, we computationally explored the mechanical, optoelectronic, and thermoelectric characteristics of halide double perovskite K₂YAgBr₆ using density functional theory up to 150 GPa applied pressure. Both the formation energy and tolerance factor ensure the structural stability of the compound. The presence of band edges at two different symmetry points indicates its indirect bandgap of 3.07 eV at ambient pressure, and the value of the band gap decreases with increasing pressure. The absorptivity and dielectric function values are increased with driving pressure. The absorption peak is shifted towards the lower energy region with increased hydrostatic pressure. The mechanical behaviors demonstrated that the material is mechanically stable and ductile, with its ductility further improved under pressure. By using the BoltzTraP code based on semi-classical Boltzmann transport theory, we estimate the thermoelectric properties of K₂YAgBr₆ under different hydrostatic pressure. The results show promising Seebeck coefficient and figure of merit, suggesting its potential for optoelectronics and thermoelectric applications.

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