First-principles study of lead-free double perovskites K2Pt(Cl/Br)6 for optoelectronic and renewable energy applications

Highlights: • Double perovskites are more stable, cheap, and suitable materials for solar cells. • The maximum conversion efficiency of light energy into electrical energy. • The absorption of light falls in the visible to ultraviolet region. • The double perovskites have high figure of merit because of large Seebeck coefficient. The density functional theory-based calculations investigate the structural, electronic, elastic, optical, and thermoelectric properties of K₂Pt (Cl/Br)₆ for renewable energy applications. The tolerance factor, formation energy, and positive frequencies of phonon dispersions ensure structural and thermodynamic stabilities. The structural parameters and elastic constants analysis show the studied compounds are anisotropic and ductile. The computed direct band gaps 2.6eV and 2.2eV for K₂PtCl₆ and K₂PtBr₆ make sure the absorption of light in ultraviolet and visible regions. Therefore, these materials are extensively used in solar cells and other optoelectronic applications. Thermoelectric properties are explored in terms of electrical conductivity, thermal conductivity, and Seebeck coefficient to enhance the figure of merit. The room temperature ZT values 0.68 and 0.72 emphasize their importance for thermoelectric applications.