Probing the electronic, optical and transport properties of halide double perovskites Rb₂InSb(Cl,Br)₆ for solar cells and thermoelectric applications

Halide-based double perovskites have recently been promoted as high-performing semiconductors for photovoltaic and thermoelectricity applications owing to their outstanding efficiency, non-toxicity and ecological stability. In the framework of this research, we have systematically investigated the structural, mechanical, electronic, optical, and thermoelectric properties of Rb₂InSb(Cl,Br)₆ double halide perovskites. Based on Born stability and tolerance factor criteria, we have found that Rb₂InSb(Cl,Br)₆ are mechanically and structurally stable. Furthermore, we have performed a comprehensive evaluation of the electronic, optoelectronic, and thermoelectric characteristics. From the electronic band structure results, Rb₂InSbCl₆ and Rb₂InSbBr₆ exhibit direct semiconducting band gaps of 1.41 ​eV and 0.53 ​eV, respectively. The optical parameters of Rb₂InSb(Cl,Br)₆ reveal that our active structures have a higher dielectric constant, with maximum absorption in the visible range reaching over 5.68 ​× ​10⁵ ​cm⁻¹ and high optical conductivity (2.19 fs⁻¹ for Rb₂InSbCl₆ and 2.14 fs⁻¹ for Rb₂InSbCl₆). Moreover, the maximum limited spectroscopic efficiency reaches an impressive value of approximately 28.0% for Rb₂InSbBr₆ and 33.7% for Rb₂InSbCl₆. The thermoelectric properties were accurately calculated using the BoltzTraP simulation package. The obtained results reveal a significant electrical conductivity, a strong Seebeck coefficient (S ​≈ ​2756 μVK⁻¹ ​at 300 ​K), and an average figure of merit close to one for both structures (ZT ​≈ ​1). Our findings suggest the versatility of these materials and could be used for a wide range of applications, including commercial solar cells and thermoelectricity.