High-Performance CH₃NH₃PbI₃-Inverted Planar Perovskite Solar Cells with Fill Factor Over 83% via Excess...

The reduction of charge carrier recombination and intrinsic defect density in organic-inorganic halide perovskite absorber materials is a prerequisite to achieving high-performance perovskite solar cells with good efficiency and stability. Here, we fabricated inverted planar perovskite solar cells by incorporation of a small amount of excess organic/inorganic halide (methylammonium iodide (CH₃NH₃I; MAI), formamidinium iodide (CH(NH₂)₂I; FAI), and cesium iodide (CsI)) in CH₃NH₃PbI₃ perovskite film. Larger crystalline grains and enhanced crystallinity in CH₃NH₃PbI₃ perovskite films with excess organic/inorganic halide reduce the charge carrier recombination and defect density, leading to enhanced device efficiency (MAI+: 14.49 ± 0.30%, FAI+: 16.22 ± 0.38% and CsI+: 17.52 ± 0.56%) compared to the efficiency of a control MAPbI₃ device (MAI: 12.63 ± 0.64%) and device stability. Especially, the incorporation of a small amount of excess CsI in MAPbI₃ perovskite film leads to a highly reproducible fill factor of over 83%, increased open-circuit voltage (from 0.946 to 1.042 V), and short-circuit current density (from 18.43 to 20.89 mA/cm²).