First-principles study on optic-electronic properties of doped formamidinium lead iodide perovskite

We have discussed the materials of solar cell based on hybrid organic-inorganic halide perovskites with formamidinium (NH₂CH=NH₂⁺ or FA) lead iodide. Firstly, we build the structure of formamidinium lead iodide (FAPbI₃) by using the material studio. By using the first-principles calculations, the energy band structure, density of states (DOS), and partial DOS (PDOS) of the hydrazine-iodide lead halide are obtained. Then, we theoretically analyze a design scheme for perovskite solar cell materials, published in[Science 354, 861 (2016)], with the photoelectric conversion efficiency that can reach 20.3%. Also, we use non-toxic elements to replace lead in FAPbI₃ without affecting its photoelectric conversion efficiency. Here in this work, we explore the energy band structure, lattice constant, light absorption efficiency, etc. After the Ca, Zn, Ge Sr, Sn, and Ta atoms replacing lead (Pb) and through comparing the spectral distributions of the solar spectrum, it can be found that FAGeI₃, FASnI₃, and FAZnI₃ have better absorbance characteristics in the solar spectrum range. If the band gap structure is taken into account, FAGeI₃ will become an ideal material to replace FAPbI₃, although its performance is slightly lower than that of FAPbI₃. The toxicity of Pb is taken into account, and the Ge element can be used as a substitute element for Pb. Furthermore, we explore one of the perovskite materials, i.e., FA_0.75Cs_0.25Sn_0.25Ge_0.75I₃ whose photovoltaic properties are close to those of FA_0.75Cs_0.25Sn_0.5Pb_0.5I₃, but the former does not contain toxic atoms. Our results pave the way for further investigating the applications of these materials in relevant technologies.