Impact of Anion Impurities in Commercial PbI₂ on Lead Halide Perovskite Films and Solar Cells

Batch-to-batch variability of commercial PbI 2 precursors, even with metal purity levels of >99.99%, is a major limitation toward achieving intra- and interlab reproducibility of lead halide-based perovskite solar cells. This work identifies that Pb(OH)I is the primary impurity that causes these adverse issues. Through a systematic investigation into the role of synthesized Pb(OH)I within Cs 0.05 (FA 0.85 MA 0.15 ) 0.95 Pb(I 0.85 Br 0.15 ) 3 perovskite films and solar cells, it is shown that this impurity induces segregated PbI 2 and δ-FAPbI 3 phases and reduces the ensuing solar cell performance characteristics. To avoid these issues, a facile, high-yield, remediation process amendable to any PbI 2 precursor batch is introduced. Through its use, reliably high performing metal halide perovskite solar cells are achieved.