Study of lead-free double perovskites X₂AgBiI₆(X = K, Rb, Cs) for solar cells and thermoelectric applications

The double perovskites became appealing over time for solar cells and optoelectronic applications due to their extraordinary optical and transport properties. Here, we investigate the optical and thermoelectric behavior of a newly developed perovskite X2AgBiI6 (X = K, Rb, Cs) DPs. To ensure structural stability, the computed tolerance factor falls in the appropriate range. The formation energy has also been incorporated for thermodynamic stability. The reported band gaps (1.35, 1.30, 1.26) eV for (K, Rb, Cs) fall in the ideal range which is extremely important for solar cells. Moreover, the studied DPs demonstrate light absorption characteristics in the visible wavelength range. The transport properties discussion has been provided in terms of electrical and lattice conductivities, Seebeck coefficient, and figure (ZT) of merit analysis. With an excellent ZT at room temperature and a suitable band gap for visible absorption, the presented DPs are promising for thermoelectric generators and solar cell applications.