Insights into the optoelectronic and thermoelectric properties of lead-free Rb2NaIrF6 double perovskite compound: A first-principles study

This study investigated the structural, electronic, elastic, mechanical, thermodynamic, optical, and thermoelectric properties of the Rb₂NaIrF₆ lead-free double perovskite compound using first-principles methods. The structural stability of the perovskite was confirmed by the Goldschmidt tolerance and octahedral factors. Dynamic stability was confirmed through the negative energy of formation and positive frequency modes of the phonon dispersion curve. The dynamic stability results suggest that the studied compound could be potentially synthesised experimentally. The Rb₂NaIrF₆ compound is a direct semiconductor with electronic band gaps within the range of 2.14–3.76 eV, computed using different approximations. The mechanical stability was confirmed by the elastic calculation results. The Rb₂NaIrF₆ compound was found to be ductile, ionic, and anisotropic. The optical properties showed that Rb₂NaIrF₆ strongly absorbs light in the ultraviolet region, which is desirable for ultraviolet-photosensitive materials in optoelectronic devices. The computed thermoelectric figure of merit of the Rb₂NaIrF₆ compound is 0.81 at 1000 K, suggesting high thermoelectric efficiency. These findings demonstrate the potential of Rb₂NaIrF₆ lead-free double perovskite compound for optoelectronic and thermoelectric applications. Therefore, our investigation offers theoretical insights that can lead to the experimental synthesis and study of Rb₂NaIrF₆ lead-free double perovskites.