Adsorption of Formic Acid on CH3NH3PbI3 Lead–Halide Organic–Inorganic Perovskites

Abstract

The adsorption kinetics of formic acid (HCOOH) was studied under ultrahigh vacuum (UHV) on lead–halide organic–inorganic perovskites (CH3NH3PbI3) supported on indium-doped tin oxide (ITO). The thin film samples were made at ambient pressure using the common liquid-phase synthesis, but samples were degassed under UHV. We studied real-world samples which do have some carbon impurities. Adsorption and decomposition kinetics were characterized with thermal desorption spectroscopy. Furthermore, samples’ composition (including impurities) were inspected under UHV with Auger electron spectroscopy and X-ray photoelectron spectroscopy. Accordingly, formic acid adsorbs molecularly at 100 K but decomposed above 600 K. On ITO or thermally decomposed perovskite samples, formic acid adsorbs only molecularly. The gas-phase species detected are consistent with a decomposition mechanism via the formation of formate (HCOO) and formyl (HCO) intermediates. The perovskite itself also decomposed thermally, but it is stabilized...