Table and Fig. show I:Pb ratios of the as-received PbI2 materials (measured by ICP-OES) varied from 8% deficient to 5% excess in iodide. Despite statistical considerations, the trend in asreceived I:Pb ratio appears reflected in the corresponding device efficiency in Fig. reported as stabilized power output (SPO). A similar trend in as-received PbI2 efficiency is observed in devices with differing perovskite compositions, processing, and architectures made by different researchers (Supplementary Figures and) confirming that the noted effects are not limited to a specific composition, architecture, nor processing route. Note that SA5 is omitted from asreceived device sets because its solubility was too low to produce films adequate for devices.