Organoammonium-Ion-based Perovskites Can Degrade to Pb⁰via Amine-Pb(II) Coordination

The degradation of alkylammonium PbII halide perovskites, in the dark and upon irradiation near room temperature, involves coordinated amine as the dominant reducing agent to yield Pb0 near room temperature, as determined by X-ray photoelectron spectroscopy (XPS). The reduction of PbII first involves amine coordination, supported by 207Pb nuclear magnetic resonance (NMR) analysis. It is shown that a PbII-amide complex is the immediate precursor of PbII reduction. Its oxidized counterpart, the imine, is formed and is characterized by NMR and gas chromatography-mass spectrometry. The "redox"process requires a β-C-H bond of the alkylamine. Amine species devoid of this moiety do not similarly reduce PbII to Pb0. The conversion of an alkylammonium moiety to the PbII-amide is proposed to occur through a sequence of photoassisted proton-transfer reactions to a lead-coordinated ligand, which is substantiated through XPS-observed PbII reduction in a family of lead bromide/iodide 2D perovskites.