Organoammonium-Ion-Based Perovskites Can M. Degrade To Pb-0 Via Amine-Pb(Ii) Coordination

The degradation of alkylammonium Pb-II halide perovskites, in the dark and upon irradiation near room temperature, involves coordinated amine as the dominant reducing agent to yield Pb-0 near room temperature, as determined by X-ray photoelectron spectroscopy (XPS). The reduction of Pb-II first involves amine coordination, supported by Pb-207 nuclear magnetic resonance (NMR) analysis. It is shown that a Pb-II-amide complex is the immediate precursor of Pb-II reduction. Its oxidized counterpart, the imine, is formed and is characterized by NMR and gas chromatography-mass spectrometry. The "redox" process requires a beta-C-H bond of the alkylamine. Amine species devoid of this moiety do not similarly reduce Pb-II to Pb-0. The conversion of an alkylammonium moiety to the Pb-II-amide is proposed to occur through a sequence of photoassisted proton-transfer reactions to a lead-coordinated ligand, which is substantiated through XPS-observed Pb-II reduction in a family of lead bromide/iodide 2D perovskites.