DFT exploration of novel direct band gap semiconducting halide double perovskites, A2AgIrCl6 (A = Cs, Rb, K), for solar cells application

Double perovskite halides are promising materials for renewable energy production, meeting the criteria to address energy scarcity issues. As a result, studying these halides could be useful for optoelectronic and solar cell applications. In this study, we investigated the structural, mechanical, thermodynamic, electronic, and optical properties of A2AgIrCl6 (A = Cs, Rb, K) double perovskite halides using density functional theory calculations with the full-potential linearized augmented plane-wave (FP-LAPW) approach, aiming to evaluate their suitability for renewable energy devices. The Goldsmith tolerance factor, octahedral factor, and new tolerance factor have confirmed the cubic stability of the predicted compounds. We have also verified the thermodynamic stability of these compounds by calculating the formation enthalpy, binding energy, and phonon dispersion curves. Additionally, Born-Huang stability requirements on stiffness constants confirmed the mechanical stability of the titled compounds. To predict the accurate optoelectronic properties, we employed the TB-mBJ potential. The electronic band structure calculations revealed that the titled halides exhibit a direct band gap semiconducting nature with values of 1.43 eV, 1.50 eV, and 1.55 eV for Cs2AgIrCl6, Rb2AgIrCl6, and K2AgIrCl6, respectively. Besides, all these compounds showed remarkably low effective electron masses, indicating their potential for high carrier mobility. Furthermore, the optical properties of A2AgIrCl6 (A = Cs, Rb, K) compounds demonstrated very low reflectivity and excellent light absorption coefficients (105 cm-1) in the visible light spectrum, suggesting their suitability as an absorbing layer in solar cells. The photoconductivity and absorption spectra of these compounds validate the accuracy of our band structure results.