A DFT computational design and exploration of novel direct band gap silver-thallium double perovskites

Abstract: Researchers have addressed the non-traditional power generation schemes as alternatives to the traditional fossil-fuel methods enormously since the scientific community has serious concerns about shortages of energy on our planet for future generations. In this scenario, the innovative materials for photovoltaic and thermoelectric device applications are required by addressing current issues of instability and efficiency. Perovskites are very popular in this regard particularly having higher power conversion efficiency of 25.2% in the case of solar cells. In the current article, we investigated innovative small direct band gap double perovskites (elapsolite) Cs$_2$AgTlX$_6$ (X= Cl, Br) with a comprehensive discussion on structural, electronic, optical, and thermoelectric properties using a first-principles approach. The compounds under investigation are found stable, efficient, and economical with alluring optical and thermoelectric properties. The higher absorption peaks in the visible range, substantial optical conductivities (~10$^{16}$ sec$^{-1}$), and a lower percentage of reflection in the visible range make these compounds fascinating for solar cell applications. Whereas large values of Seebeck coefficients, electrical conductivities, the figure of merits (greater than unity), and small values of thermal conductivities suggest the applications of these compounds in thermoelectric generators.