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We report solvothermal preparations of nanocrystalline CuIn 1-x Al x Se 2 materials prepared from the reaction of Se, CuX 2 (X = Clor stearate), InCl 3 , and Al(oleate) 3 in refluxing oleylamine for 30 minutes to 3 hours. Scanning electron microscopy (SEM) images reveal morphologies consisting of hexagonal plates (100-400 nm diameter) with smaller isomorphic nodules. Micro-Raman spectroscopy, x-ray diffraction, and optical bandgap data are consistent with Al 3+ incorporation into the chalcopyrite structure. For aluminum-containing reactions, product Al/(In+Al) ratios are estimated to be between 0.15 and 0.35 regardless of the indiumaluminum stoichiometry employed in the reaction. When Se is added to the reaction last, the reaction pathway involves an early-formed Cu 2-x Se(s) intermediate that appears to react with Inand Al-containing species simultaneously. This intermediate is avoided when heating InCl 3 , Al(oleate) 3 , and Se together prior to Cu addition, but the final product includes Se contamination that must be removed or reacted by annealing.

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Many reported CuIn1-xGaxSe2 (CIGS) thin films for high-efficiency solar cells have been prepared via a two-stage process that consists of a high-vacuum film deposition step followed by selenization with excess H2Se gas or Se vapor. Removing toxic gas and high-vacuum requirements from this process would greatly simplify it and make it less hazardous. We report the formation of CuIn1-xGaxSe2 (x = 0, 0.25, 0.50, 0.75, 1.0) thin films achieved by rapid thermal annealing of spray-deposited CuIn1-xGaxS2 and Se in the absence of an additional selenium source. To prepare the Se layer, commercial Se powder was dissolved by refluxing in ethylenediamine/2,2-dimethylimidizolidine. After cooling to room temperature, this mixture was combined with 2-propanol and the resulting colloidal Se suspension was sprayed by airbrush onto a heated glass substrate. The resulting film was coated with nanocrystalline CuIn1-xGaxS2 via spray deposition of a toluene-based “nanoink” suspension. The two-layer sample was annealed at 550 oC in an argon atmosphere for 60 minutes to form the final CIGS product. Scanning electron microscopy images reveal that film grains are 200-300 nm in diameter and comparable to sizes of the reactant CuIn1-xGaxS2 nanoparticles. XRD patterns are consistent with the chalcopyrite unit cell and calculated lattice parameters and A1 phonon frequencies change nearly linearly between those for CuInSe2 and CuGaSe2.

We describe the effects of alkyl phosphonate surface coatings applied to LiMnxNiyCo1-x-yO2 (NMC) cathode materials on battery performance. A homologous series of alkyl phosphonic acids with hydrocarbon chains ranging from ethyl (C2) to octadecyl (C18) were solution grafted onto the surface of NMC cathode particles. For each phosphonic acid, we observed comparable grafting densities onto the NMC surface except for the hexyl phosphonic acid as demonstrated by XPS analyses. Analyses of alkyl phosphonate coatings using diffuse reflectance infrared fourier transform spectroscopy (DRIFTS), showed that crystallinity of the coating layer increases with alkyl chain length. We fabricated cathodes comprising NMC coated with various alkyl phosphonates, incorporated them into half-cells, and assessed their electrochemical performance by subjecting them to 100 charge/discharge cycles and to charge/discharge rate performance tests. Electrochemical impedance spectroscopy (EIS) analyses of alkyl phosphonate-coated cathodes before and after the rate tests revealed that the long chain alkyl phosphonate coatings mitigate electrolyte degradation (1 M LiPF6 in ethylene carbonate/dimethyl carbonate) at the electrode surface. However, cathodes with long chain alkylphosphonate coatings exhibit poor high C-rate performance as compared to the shorter alkylphosphonate coatings. These findings are rationalized in terms of the crystallinities of the different coating layers.