The physical supercritical fluid deposition is a method of thin film deposition that allows high molecular weight materials to be deposited onto curved and flexible substrates to form patterns with high spatial resolution. The preferred mode of deposition relies on a maximum in the isobaric solubility to precipitate material onto a heated substrate. This typically occurs at pressures exceeding the critical pressure of the solvent, hence the technique is termed supercritical fluid deposition. Because the technique relies on the solubility properties of the solvent-solute system, one of the most important factors in determining the optimized deposition conditions is solvent selection. Here, we demonstrate that for poly(3-hexyl thiophene) (P3HT), there are three qualitatively different types of solvents, only one of which is appropriate for physical supercritical fluid deposition on heated substrates. Over-powered solvents are ineffective for the physical supercritical fluid deposition because they lack a maximum in the isobaric solubility. Underpowered solvents are unable to dissolve the deposition material. Optimum solvents dissolve the material effectively and exhibit a maximum isobaric solubility over the working temperature range of the deposition chamber. In addition, we demonstrate the effect of adding an overpowered solvent to an underpowered solvent and an optimum solvent. Only the mixture with an optimum solvent shows the necessary characteristics for physical supercritical fluid deposition. In sum, the work demonstrates clear guidelines for solvent selection that will allow for the deposition of a wider range of materials. Furthermore, the films are deposited to achieve better uniformity and smoothness.
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Thesis advisor: Kaake, Loren
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