PbI2 Reagent Impurities Catalyze Mixed-Cation Halide Perovskite Ink Degradation

Non-negligible K, acetate (OAc–), and nitrate (NO3–) impurities have been identified in commercially available PbI2 reagents, plausibly remnant from synthesis. Here, we characterize the individual impact of each of these impurities on the relative rate of the methylammonium (MA) condensation reaction with formamidinium (FA) to release N-methylformamidinium (MFA), a main degradation pathway of mixed-cation halide perovskite inks, emphasizing the need to better control purity in halide perovskites.