Electron band tuning of organolead halide perovskite materials by methylammonium and formamidinium halide post-treatment for high-efficiency solar cells.

Perovskite crystals post-treated with methylammonium and formamidinium halide materials were compared. The bandgap energy of perovskites changed upon incorporation of CH5N2+, Br-, and Cl- ions. Perovskites treated with formamidinium iodide yielded the best efficiency of 20.06% due to an increase in photocurrent density by decreased bandgap energy.