Surface Characterization and Reactivity of Methylammionium Lead Iodide

Zielinski, Kenneth M

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Surface Characterization and Reactivity of Methylammionium Lead Iodide

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We quantify the chemical species present at and reactivity of the tetragonal (100) face of single-crystal methylammonium lead iodide, MAPbI3(100). MAPbI3 is an ABX3 perovskite, experiments utilized the orthogonal reactivity of the A+-site cation, the B2+-site cation, and the X–-site halide anion. Ambient-pressure exposure to BF3 solutions probe the reactivity of interfacial halides. Reactions with p-trifluoromethylanilinium chloride probe the exchange reactivity of the A+-site cation. The ligand 4,4’-bis(trifluoromethyl)-2,2’-bipyridine probe for interfacial B2+-site cations. Fluorine features in x-ray photoelectron spectroscopy (XPS) quantify reaction extents with each solution-phase species. XP spectra reveals adsorption of BF3 indicating surface-available halide anions on tetragonal MAPbI3(100) and preliminary examinations on the (112), (110), and thin-film surfaces. Temperature-programmed desorption (TPD) established a ~200 kJ mol–1 desorption activation energy from tetragonal MAPbI3(100). Adsorption of the fluorinated anilinium cation includes no concomitant adsorption of chlorine as revealed by the absence of Cl 2p features within the limits of XPS detection on the tetragonal (100) and (112) faces with no discernable exchange in preliminary experiments on tetragonal (110). Within detection limits, bipyridine ligand demonstrate no adsorption to tetragonal MAPbI3(100) or (112), while it does demonstrate significant adsorption on the (110) in preliminary experiments. We discuss the present results in the context of interfacial stability, passivation, and reactivity for perovskite-based energy conversion materials and some preliminary investigations into bilayer graphene-based dye sensitized photovoltaic materials.

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