Investigation of strontium doping in formamidinium lead iodide: electronic and optical properties*

Due to toxicity concerns of Pb-containing materials in solar cells, Pb-free and stable organic-inorganic perovskites have been a highly desirable option for space and commercial solar cell applications; however, Pb-containing perovskites are among the higher-performing materials for solar cells to date. One possible method for retaining the preferable optoelectronic properties of purely Pb-containing materials while reducing their toxicity is the partial substitution of Pb⁺² by the homovalent cation, Sr⁺². Given the almost identical bonding pattern and ionic radii of Pb and Sr, interchanging the two has been achieved. Upon substitution by the non-toxic alkaline earth metal, there is increased thermal/environmental stability and an inherent reduction in overall toxicity of the host material. Here we utilize first-principles DFT methodologies to investigate the effects of Sr-doping on the electronic and optical properties of FAPbI₃, such as the electronic structure, bandgap, dielectric function, absorption spectra, reflectivity, and conductivity of the doped/undoped materials. These results can provide insight into the role that partial substitution of the Pb-site in perovskite materials has in the development of non-toxic Pb-free materials for solar cell applications.