摘要： The conventional precursor mixture based on highly pure and expensive PbI2 (purity>99.99%) is problematic in commercializing perovskite solar cells (PSC) because of a large deviation in the batch-to-batch photovoltaic performance due to underlying non-stoichiometry and/or non-perovskite phase. Here, we report on reproducible efficiency (>21%) PSCs based on the ambient-temperature-stable delta-phase FAPbI3 powder, synthesized by reacting PbI2 (either home-made or low-grade commercial product with purity <99%) with formamidinium iodide (FAI) at room temperature (~93% yield). X-ray diffraction patterns confirms that annealing the spin-coated film leads to phase purity of cubic alpha FAPbI3. As compared to the conventional precursor mixture based on PbI2 (purity = 99.9985%), a significantly reduced defect in the powder-based film is responsible for the stable and reproducible efficiency. In addition, homogeneous light-intensity-dependent surface photocurrent contributes to the reproducibility of photovoltaic performance. The quasi-steady-state PCE of 21.07% is certified from the device based on FAPbI3 powder.