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-to batch 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 delta-phase FAPbI(3) powder, synthesized by reacting PbI2 (either homemade or low-grade commercial product with purity <99%) with formamidinium iodide (FAI) at room temperature (similar to 93% yield). X-ray diffraction patterns confirm that annealing the spin-coated film leads to phase purity of cubic alpha FAPbI(3). As compared to the conventional precursor mixture based on PbI2 (purity = 99.9985%), significantly reducing defects in the powder-based film is responsible for the stable and reproducible efficiency. In addition, the homogeneous light-intensity-dependent surface photo current contributes to the reproducibility of photovoltaic performance. The quasi-steady-state power conversion efficiency of 21.07% is certified for the device based on FAPbI(3) powder.