First-principles investigation of direct band gap double perovskite halides A2AgIrCl6 (A = Cs, Rb, K) for enhanced photovoltaic performance

Abstract

This study carefully investigates the structural, electrical, optical, mechanical, and thermodynamic features of A₂AgIrCl₆ compounds (A = Cs, Rb, K) that belong to double perovskite halides (DPH) utilizing density functional theory (DFT). The stability of the predicted compounds in the cubic structure was confirmed through calculations involving the Goldschmidt tolerance factor, octahedral factor, and the new tolerance factor. Analysis of formation enthalpy, binding energy, phonon dispersion relations, and ab initio molecular dynamics (AIMD) results suggests thermodynamic and dynamic stability, indicating possible synthetic viability that should be verified experimentally. To predict the accurate optoelectronic properties, we employed the Tran and Blaha modified Becke-Johnson (TB-mBJ) potential. The electronic band structure study demonstrated that the studied halides exhibit direct band gap semiconductor with band gap values of 1.43 eV, 1.50 eV, and 1.55 eV for Cs₂AgIrCl₆, Rb₂AgIrCl₆, and K₂AgIrCl₆, respectively. The relatively low electron effective masses suggest favorable carrier transport characteristics. In addition, the calculated exciton binding energies and exciton radii indicate a tendency toward efficient generation of free charge carriers. The optical investigation further demonstrated that the A₂AgIrCl₆ compounds exhibit low reflectivity and high absorption coefficients (on the order of 10⁵ cm⁻¹) in the visible region, highlighting their potential for optoelectronic applications. The computed elastic constants fulfill the Born–Huang criteria, confirming mechanical stability, while further analysis indicates ductile and anisotropic behavior. Overall, the calculated results suggest that the A₂AgIrCl₆ compounds exhibit promising optoelectronic descriptors favorable for further experimental and device-oriented evaluation.