Achieving Reproducible and High-Efficiency (>21%) Perovskite Solar Cells with a Presynthesized FAPbI3 Powder

The conventional precursor mixture based on highly pure and expensive PbI2 (purity >99.99%) is problematic in commercializing perovskite solar cells (PSCs) because of a large deviation in the batch-tobatch photovoltaic performance due to underlying nonstoichiometry and/ or the nonperovskite phase. Here, we report on reproducibly efficient (>21%) PSCs based on the ambient-temperature-stable δ-phase FAPbI3 powder, synthesized by reacting PbI2 (either homemade or low-grade commercial product with purity ≪99%) with formamidinium iodide (FAI) at room temperature (∼93% yield). X-ray diffraction patterns confirm that annealing the spin-coated film leads to phase purity of cubic α FAPbI₃. As compared to the conventional precursor mixture based on PbI₂ (purity = 99.9985%), significantly reducing defects in the powderbased film is responsible for the stable and reproducible efficiency. In addition, the homogeneous light-intensity-dependent surface photocurrent contributes to the reproducibility of photovoltaic performance. The quasi-steady-state power conversion efficiency of 21.07% is certified for the device based on FAPbI₃ powder.