Analytical Evaluation of Lead Iodide Precursor Impurities Affecting Halide Perovskite Device Performance

Mirroring established semiconductor technologies, halide perovskite materials synthesized from higher quality reagents display improved optoelectronic performance. In this study, we performed a semiquantitative analytical characterization of five different commercial lead iodide sources to determine the identity and concentration of impurities that affect perovskite devices. It was possible to single out acetate (OAc) and potassium (K) as key species in as-received materials, both plausibly remnant from synthesis or purification. We removed these impurities through aqueous recrystallization revealing contrasting impacts on device performance: removal of OAc was beneficial but reducing K could be detrimental. This observation indicates that the highest purity lead iodide does not guarantee the highest performing perovskite material, since certain extrinsic impurities, such as KI, can improve device performance. Fundamental and applied studies will both benefit from improved purification procedures coupled with analytical studies to better understand and control the effects of individual impurities in halide perovskite materials.