First-principles study on azetidinium tin iodide <?A3B2 pi6?>perovskites for photovoltaics

Recently, organic-inorganic halide perovskite has received much attention because of its low cost and high efficiency in solar cells. Herein, we have performed the first-principles investigation to explore the structure, stability, electronic properties, and optical properties of AZBI₃ (B = Pb, Sn, Ge) and AZSnI_{3−<italic>y</italic>}Br_{<italic>y</italic>} (<italic>y</italic> = 1, 2, 3) perovskites. The tolerance factor (<italic>τ</italic>), octahedral factor (<italic>μ</italic>), and formation energies were calculated to evaluate the structural thermodynamic stability of six perovskites. The band gap and structures have been obtained, indicating that Sn/Ge replacement and Br-doping decrease the band gap. Similarly, B-site replacement and X-site doping affect the optical properties. All the absorption spectra of six perovskites cover the visible light region, and AZSnI₃/AZSnI₂Br perovskites are the most outstanding. They are likely to be good candidates for use in solar cells.