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Highly Resolved Nanostructured PEDOT on Large Areas by Nanosphere Lithography and Electrodeposition

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journal contribution
posted on 07.10.2015, 00:00 by Van-Quynh Nguyen, Delphine Schaming, Pascal Martin, Jean-Christophe Lacroix
Poly­(ethylenedioxythiophene) (PEDOT) films were electrodeposited galvanostatically from an EDOT/sodium dodecyl sulfate solution in water, through a carboxylated polystyrene template monolayer self-assembled on ITO, after which the template was dissolved away in tetrahydrofuran. Analysis of the films by scanning electron microscopy and atomic force microscopy reveals large-area PEDOT honeycomb structures. The morphology of these structures was varied electrochemically, as the effective thickness and, surprisingly, the shape of the honeycomb arrangement depend on the polymerization time. Using nanospheres of 1 μm diameter and charge densities between 12 and 30 mC cm–2 for electrodeposition generates PEDOT hexagons with very thin rectilinear walls 30–35 nm-thick and 800 nm-long, whereas at higher charge densities, circular bowls are created with 60 nm walls separating adjacent bowls; triangular areas as small as 0.02 μm2 develop at the intersection of three nanospheres. These morphologies are specific to the use of carboxylated PS spheres and a water-based solution with a surfactant in the galvanostatic electrodeposition mode. Using smaller nanospheres, i.e. 500 nm in diameter, makes it possible to reach PEDOT hexagons with rectilinear walls as small as 11–17 nm-thick and 300 nm-long; circular bowls with 25–35 nm walls separating adjacent bowls and triangular areas as small as 0.003 μm2 can also be generated. The wettabilities of the surfaces depend markedly on the pore depth of the PEDOT nanostructure, with contact angles going from 82° to 130° with increasing pore size. Finally these nanostructured PEDOT electrodes were used in Grätzel-type dye-sensitized solar cells (DSSCs) as Pt-free counter-electrodes, with an increase in the yield from 7.0 (bulk PEDOT) to 8.1%.