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The moisture barrier properties of large-grain single-layer graphene (SLG) deposited on a Cu(111)/sapphire substrate are demonstrated by comparing with the bare Cu(111) surface under an accelerated degradation test (ADT) at 85 °C and 85% relative humidity (RH) for various durations. The change in surface color and the formation of Cu oxide are investigated by optical microscopy (OM) and X-ray photoelectron spectroscopy (XPS), respectively. First-principle simulation is performed to understand the mechanisms underlying the barrier properties of SLG against O diffusion. The correlation between Cu oxide thickness and SLG quality are also analyzed by spectroscopic ellipsometry (SE) measured on a non-uniform SLG film. SLG with large grains shows high performance in preventing the Cu oxidation due to moisture during ADT.

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The role of an additional solvent thiosemicarbazide (TSC) in the synthesis of a highly crystallized inorganic–organic halide FA0.8Cs0.2PbIxBr3 − x perovskite using the co-solvent N,N-dimethylformamide/1-cyclohexyl-2-pyrrolidone has been investigated. Ellipsometry combined with x-ray diffraction and FTIR spectroscopy was used for characterization purposes. The average crystal grain size increased from several hundred nanometers to 1–1.5 μm with increasing content of TSC in the co-solvent. Ellipsometry and FTIR spectroscopy revealed that the as-deposited perovskite film before thermal annealing was distorted and featured a large number of voids; also, the Pb ions formed complexes with the C˭S groups in TSC, which suppressed the excessive nucleation. Removal of the co-solvent at the thermal annealing stage facilitated the rearrangement of the [Pb(IxBr3 − x)6]4− octahedral structure from a zero-dimensional to a three-dimensional network, which enhanced crystal grain growth.

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