The modeling of perovskite materials $CsPbX_3$ (X = I, Br) by changing the concentration of halide : experimental and DFT study

In recent years, perovskites have quickly gained popularity in applications related to photonic devices and in photovoltaic applications. Over the last several years, the efficiency of photovoltaic (PV) cells based on perovskites has matched the efficiency of PV cells based on silicon. $CsPbBr_{3}$ perovskite is gaining more and more popularity, but due to the too large band gap value, its use in photovoltaics is difficult. Another perovskite, very intensively researched and giving hope for further development of photovoltaics, is $CsPbI_{3}$. The $CsPbI_{3}$ band gap is smaller than the $CsPbBr_{3}$ band gap and more suitable for photovoltaic applications. However, $CsPbI_{3}$ is unstable under the conditions of solar cell operation. To reduce the band gap value and increase the perovskite stability, very intensive research, both theoretical and experimental, is devoted to structures with mixed halides, i.e., a mixture of bromine and iodine with the general formula $CsPbBr_{x}I_{3−x}$. Computational methods based on DFT have been successfully used for many years to determine the parameters and properties of materials. The use of computational methods significantly reduces the costs of the research performed compared to experimental techniques. The aim of this work is to understand the band gap changes based on DFT calculations as well as XRD and UV-Vis experiments for $CsPbBr_{3}$, $CsPbI_{3}$, and $CsPbBr_{x}I_{3x}$ perovskites.