Adel MENEDJHI2022-03-292022-03-292022http://dspace.univ-msila.dz:8080//xmlui/handle/123456789/28469Our work focused on studying the electronic and optical properties of lead-free halide double perovskite materials Cs2AgInX6 (X = Cl,Br) and Cs2AgBiBr6 , These properties help to obtain the required photovoltaic and optoelectronic properties of these materials. Our computations will be based on the first-principles calculations Using castep code within GGA and hybrid functional (B3LYP) Our calculations showed that compound Cs2AgBiBr6 has an indirect band gap, which makes it unsuitable for photovoltaic applications. As for compound Cs2AgInCl6, the calculations showed that it has a direct band gap (Г → Г) with a value of 3.62 eV, but it is considered a discouraging result because of its high value, so it is not suitable for applications in the field of solar energy while the results of the Cs2AgInBr6 were encouraging and promising as the calculations gave a small Г to Г direct band gap in the visible range 1.427 eV for Cs2AgInBr6 and The optical absorption coefficient has been determined showing a high-absorption (> 104 cm-1) with a wide absorption band suggesting that the material of interest-based solar cells may reach a good solar efficiency. But the Synthesis of this material has not yet been achieved. In addition, our theoretical results showed that it is dynamically unstableThesis