Optoelectronic and transport properties of Na₂CuInY₆ (Y = cl, br, I) lead-free double perovskites for infrared imaging and remote sensing

The suitability of halide-based double perovskites for implementation in infrared detectors and thermoelectric devices arises from their inherent environmental stability, non-toxic nature, and demonstrable performance. In the present investigation, our focus centers on an exploration of the structural stability and mechanical attributes intrinsic in Na₂CuInY₆ (Y = Cl, Br, I) within its cubic phase utilizing DFT. The structural and thermodynamic stability is investigated by computation of tolerance factor and enthalpy of formation. Our methodology encompasses comprehensive calculations of elastic constants based on Born stability criteria that help to understand the mechanical behavior and ductile nature of these compositions. Notably, our scrutiny of the electronic band structure reveals the presence of a direct semiconducting bandgap ranging between 1.30 and 0.36 eV. This distinctive feature holds a pivotal role in facilitating optoelectronic applications because of its pronounced role in absorption within the infrared spectrum. Remarkably, our investigation into the dielectric constant allows us to pinpoint the region of maximal light absorption within the visible spectrum. Lastly, using the BoltzTraP package, we computed the thermoelectric properties of the material and noticed an almost constant value of ZT in the wide range of temperatures highlighting the large range of workability of these compositions for thermoelectric device applications.