Organoammonium-Ion-based Perovskites Can Degrade to Pb⁰ via Amine–Pb(II) Coordination

Abstract

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 207 Pb 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 β-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.

2D Pb‐Halide Perovskites Can Self‐Heal Photodamage Better than 3D Ones

“…This explanation is based on the observation that exposing thin films of BA 2 PbI 4 to 375 nm radiation (25 mW cm −2 , for 1 h) was found to reduce Pb II to Pb 0 (while releasing HI) via a reaction with BA. [ 33 ] However, this referenced case study involved surface chemistry of an open polycrystalline system (from which degradation products are able to escape), while our study reflects processes in the bulk of a highly crystalline sample. Therefore, the main difference to keep in mind is that degradation in/on polycrystalline thin films is likely to be irreversible if mass conservation is not guaranteed, while in the bulk degradation products remain spatially confined close to the damage site, which greatly helps SH.…”

“…[ 22 ] The Pb II to Pb 0 reaction requires the presence of a β‐CH bond in the ammonium cation, which exists in BA. The results in the cited study [ 33 ] show that this mechanism for Pb II reduction to Pb 0 (under the conditions specified above) is more efficient than the known PbI 2 photolysis (to Pb 0 and I 2 ). If this reaction takes place as a result of the 2P excitation of C4N1 and C4N3, some of the Pb II and BA could react.…”

“…In the report on BA-dependent Pb II → Pb 0 reduction, [33] it was argued that the PbI 2 photolysis into Pb 0 and I 2 is less efficient than a direct amine-based pathway of Pb II reduction to Pb 0 , in which case the following reduction reactions take place:…”

Construction of Polyoxometalate‐Based Material for Eliminating Multiple Pb‐Based Defects and Enhancing Thermal Stability of Perovskite Solar Cells

“…The high‐resolution XPS are performed to investigate the interaction between the dopants and perovskite crystal. Obviously, the characteristic peaks of Pb 0 , locating at 141.1 and 136.3 eV, [ 23 ] disappear after doping with CoW 12 @MIL‐101 and CoW 12 , which indicates that metallic Pb 0 has been successfully oxidized (Figure 3c). Meanwhile, compared to the pristine film, the ratio of Pb 0 /(Pb 0 + Pb 2+ ) in the MIL‐101 doped perovskite film is reduced from 3.1 to 2.5%, suggesting the Pb 0 passivation ability of MIL‐101.…”

Defect Passivation through Cyclohexylethylamine Post-treatment for High-Performance and Stable Perovskite Solar Cells

“…We attribute the downfield shifts to the connection of CHEA to a more negatively charged lead ion. Based on the changes in chemical shifts, it can be determined that CHEA and PbI 2 form a strong electrostatic force . Due to the strong electrostatic force, the film surface PbI 2 was passivated by CHEA and thus decreased the defects and improved the quality of the films.…”