Combined Ultraviolet Ozone and Thermally Activated Formamidinium Iodide Solution to Fabricate Large Grain FAPbIBrCl Films.

In this report, we report the fabrication of a large grain and high crystallinity perovskite film by combined ultraviolet-ozone (UVO) and thermal treatment of formamidinium iodide solution during the fabrication of formamidinium lead halide (FAPbIBrCl) films by a two-step deposition method. In this process, lead halide films were treated with UVO-treated FAI at different times. In addition, we have observed that hot-casting of UVO-assisted FAI nucleates the α-FAPbI phase in as-prepared films. Again, we observed that the annealed hot-cast UVO-assisted FAI increased the grain size and crystallinity in the films. It was observed that the perovskite film fabricated using 10 min UVO-treated FAI solution shows the highest power conversion efficiency (PCE) up to 17.74%. Furthermore, the perovskite film fabricated with the hot-cast at 120 °C with the 10 min UVO-treated FAI solution improved the PCE to 19.22%. This finding would help with fabrication of large grain, smooth, uniform, and pinhole perovskite films by combining UVO and thermally assisted FAI solution.