387032 In-Situ Polymerization of Functional Materials through CVD Pathway for Energy and Clean Water Resources

Sunday, November 16, 2014
Galleria Exhibit Hall (Hilton Atlanta)
Siamak Nejati, Department of Chemical and Environmental Engineering, Yale University, New Haven, CT

Polymers are versatile materials with diverse application in many different disciplines. However the current emerging technologies that rely on nanoscale materials fabrication pose a new challenge in polymer integration into devices. Solar cells, batteries, and capacitors with their mesoscopic dimension are good examples. The solvent intractability makes the integration of polymers into various devices with nanostructured electrodes very cumbersome. Here we rely on Initiated and oxidative chemical vapor deposition ( iCVD/oCVD)  as unique, solvent free method that enable polymerization and coating in one step to address the current challenges facing device fabrication at nanoscale metric regime.

Here we demonstrate how in-situ polymerization using chemical vapor deposition (CVD) can be utilized to integrate polymers within photoanode of a dye senstitzed solar cell. The importance of polymer chemistry investigated by integrating different polymer electrolytes such as poly (2‐hydroxyethyl methacrylate) (PHEMA), poly (glycidyl methacrylate)(PGMA), and poly(4-vinylpyridine) (P4VP) into cell architecture. For all the three polymers deposited, we found that fill quality which is defined as the ratio of the volume occupied by polymer over the pore volume realizes an optimum as a function of monomer surface availability. The observed phenomena attributed to the difference in sticking coefficient and surface diffusivity of the monomers. The importance of the interfacial energetic studied using different side chain pendants group and the result compared with the simulation result of our first principal modeling of the cell as a pesudohomogenous medium. We further applied our unique oCVD process to enable step polymerization of conjugated polymer with exceptional and tunable properties. Highly non-soluble unsubstituted polythiophene was deposited with measured conductivity as high as 70 S/cm, which is an indication of low degree of defect. The charge storage capacity of the polymer deposited within nanostructed electrode was evaluated and proved to be enhanced due to the nanostructue effect and nanoconfinement. We used our finding and integrate polythiophene within conventional super-capacitor electrode. A 250% increase in volumetric capacitance was realized when the polymer loading to matrix mass was optimized.  We further synthesize highly conductive Poly(3,4-ethylenedioxythiophene) (PEDOT)  with near metallic conductivity. The importance of processing parameter on conductivity and the film composition was studied and the reason behind high conductivity of the as deposited film attributed to the overoxidation state of polymer that is stabilized with the oxidant complexes imbedded within the film. The highly conductive film was used as a hole transport media in a all solid state solar cell.  A titania mesoporous electrode was deposited on a 50 nm compact layer of titanium dioxide which served as the electron transport layer and thin coating of dedoped oCVD polythiophene was used as absorber layer. The PEDOT with high conductivity was deposited on this assembly and the cell was fabricated using a gold contact on the top of the PEDOT layer. The measured photocurrent efficiency of 0.8% without any optimization was realized. To further benefit from novel iCVD process the potential application of the iCVD in fabricating microporous membrane for membrane distillation (MD) was examined. The exceptional coating ability of iCVD to deposit thin polymer layer on a hydrophilic microporous support and converting the surface to superhydrophic state proved the practicality of this approach for MD membrane fabrication application.

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