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Lead‐free double perovskites are unique materials for transport and optoelectronic applications that use clean resources to generate energy. Using first‐principle computations, this study thoroughly investigates the structural, thermoelectric, and optical attributes of A2TlAgF6 (A = Rb, Cs). Tolerance factor and formation energy estimates are used to verify that these materials exist in the cubic phase. Elastic constants with high melting temperature values are ductile when evaluated for mechanical stability using the Born stability criterion. The optical absorption band is adjusted from 2 to 4 eV via band gaps of 1.88 and 1.99 eV, as indicated by band structures. Analysis of optical properties reveals perfect absorption in the visible spectrum, whole polarization, and low optical loss. Furthermore, thermoelectric properties are assessed at 300, 500, and 700 K in the range of −0.5 to 3 eV for chemical potential (μ). The materials exhibit significant improvements in the Figure of Merit scale due to their elevated electrical conductivity, Seebeck coefficient, and extremely low thermal conductivity values. [ABSTRACT FROM AUTHOR]

The present investigation thoroughly evaluates the structural, optoelectronic, elastic, and transport properties of Rb2CuSbZ6 (where Z = F, Br, and I). The assessment includes the application of the Born-Huang criterion, the tolerance factor, and the formation energy to ensure the thermodynamic, structural, and mechanical stability of the compounds. Analysis of elastic and mechanical parameters supports their ductile nature and directed bonding capabilities. Utilizing the Tran and Blaha-modified Becke-Johnson approximations, the study estimates the band gap values of Rb2CuSbF6, Rb2CuSbBr6, and Rb2CuSbI6 as 1.37 eV, 0.72 eV, and 0.36 eV, respectively, indicating characteristics of indirect bandgap semiconductors. Extensive scrutiny of optical parameters reveals remarkable dielectric and absorption capabilities within the visible light spectrum. Consequently, Rb2CuSbZ6 (where Z = F, Br, and I) double perovskites are recommended for utilization in solar cell applications and optoelectronic devices. Furthermore, assessments of their transport properties indicate that the examined compounds display attributes of a p-type semiconductor, alongside an exceptionally low thermal conductivity and a high power factor, making them highly suitable for energy harvesting devices. [ABSTRACT FROM AUTHOR]

• Na 2 CuAsX 6 (X = F, Cl, Br, and I) double perovskites (DPs) are stable in the cubic phase. • They have indirect band gaps of 1.28, 1.14, 0.85, and 0.52 eV, respectively. • These materials are appropriate for solar cell applications exhibiting a significant absorption in the visible region. • Na 2 CuAsX 6 (X = F, Cl, Br, and I) exhibit p-type semiconductor characteristics. • These perovskites possess exceptional physical features to serve as sustainable green energy alternatives. The current research is intended to investigate the physical properties of the Na 2 CuAsX 6 (X = F, Cl, Br, and I) double perovskites using the density functional theory (DFT) framework implemented in the WIEN2k code. Herein, the structural configuration, electronic, optical, thermoelectric, and thermodynamic features are thoroughly discussed. The structural investigation utilized the Murnaghan equation of state (EOS) and the generalized gradient approximation (GGA). The thermal and phase stability has been verified by the formation enthalpy and tolerance factor. The perovskites Na 2 CuAsF 6 , Na 2 CuAsCl 6 , Na 2 CuAsBr 6 , and Na 2 CuAsI 6 exhibit semiconductor properties characterized by indirect band gaps of 1.28, 1.14, 0.85, and 0.52 eV, respectively. An extensive examination of the optical characteristics suggests the possible appropriateness of these materials for photovoltaic applications. Double perovskites exhibit a significant absorption in the visible spectrum. Thermodynamic properties have demonstrated the thermal stability of analyzed perovskites even at high temperatures. Additionally, the thermoelectric properties have been determined at specific temperatures and chemical potentials, indicating the p-type nature of studied perovskites. The figure of merit (ZT) values at 300 K are determined to be 0.79, 0.76, 0.77, and 0.80, suggesting Na 2 CuAsX 6 may be sustainable thermoelectric materials with excellent performance. Consequently, the examined materials can serve as sustainable candidates for solar energy and wasted heat recovery applications. [ABSTRACT FROM AUTHOR]

This article comprehensively explores the structure, stability, mechanical, optoelectronic, and thermoelectric aspects of the emerging double perovskites A2YCuZ6 (A = Rb, Cs and Z = Cl, Br). The structural and mechanical characteristics are estimated using the PBE-GGA functional, whereas the optoelectronic and thermoelectric characteristics are computed using the modified Becke and Johnson potential. Tolerance factor, formation energies, and Gibbs free energies have validated the cubic phase and thermodynamic stability. The anticipated elastic values indicated that all the materials exhibited mechanical stability, ductility, and anisotropic behavior. The computed electronic features verified that Rb2YCuCl6, Rb2YCuBr6, Cs2YCuCl6, and Cs2YCuBr6 have indirect band gaps of 1.95, 1.30, 1.55, and 1.2 eV, respectively. This work also explores the optical response in the energy range 0 to 6 eV in terms of polarization, refractive index, absorption, and optical conduction. The visible and ultraviolet ranges of light are both significantly absorbed, making these materials optimal for use in solar systems. The BoltzTraP code has been used to calculate the transport parameters, demonstrating the p-type semiconductors nature of these materials. Further, the significant merit values of 0.77, 0.83, 0.82, and 0.81 at room temperature for analyzed materials suggest their potential applicability in thermoelectric devices. Hence, the investigated double perovskites, which are not empirically validated, have been recommended as extremely suitable alternatives for creating various energy conversion applications. [ABSTRACT FROM AUTHOR]