First-principles investigation of structural, electronic, optical and thermoelectric performance of stable inorganic double perovskites A2AlAgBr6 (A=K, Rb, Cs) for energy harvesting

In this work, the structural, electronic, optical and thermoelectric properties of Cs₂AlAgBr₆, K₂AlAgBr₆ and Rb₂AlAgBr₆ have been investigated using WIEN2k code. All the three double perovskites show stability. The stability is confirmed by calculating their formation energy, tolerance factor and molecular dynamic simulations. The electronic properties revealed the understudy compounds as semiconductors of direct band gap of 2.62, 2.61 and 2.59 eV for Cs₂AlAgBr₆, K₂AlAgBr₆ and Rb₂AlAgBr₆, respectively. The absorption band of our compounds is mostly in the ultraviolet energy range which is particularly significant for optoelectronic devices. The studied double perovskites exhibit a large Seebeck coefficient and electrical conductivity, which is significant for the high figure of merit. These properties make them particularly suitable for thermoelectric (TE) devices and other photovoltaic applications, as their high figure of merit at low temperatures opens up new possibilities for these materials.