Abstract
Double perovskites have attracted enormous attention recently due to the use in optoelectronic devices. Double perovskites have stable and simple crystal structure which make them even more interesting for investigation. In the present work, X2AgTlCl6 (X = Rb, Cs) halide double perovskites are studied. The calculated energy band gaps for Rb2TlAgCl6 and Cs2TlAgCl6, respectively are 0.78 eV and 0.74 eV and therefore can be very suitable for the optoelectronics applications. Cl-3p mainly controls the electronic properties of these compounds. Compounds show single peaked behavior in the energy range 0-5 eV. The optical structures shifted towards lower energy by replacing the cation in going from Rb to Cs. Compounds show high figure of merits (0.72, 0.68) in the high temperature range. Therefore, these compounds can also be used for thermoelectric applications.