Conformal coverage of poly(3,4-ethylenedioxythiophene) films with tunable nanoporosity via oxidative chemical vapor deposition

Abstract

Novel nanoporous poly(3,4-ethylenedioxythiophene) (PEDOT) films with basalt-like surface morphology are successfully obtained via a one-step, vapor phase process of oxidative chemical vapor deposition (oCVD) by introducing a new oxidant, CuCl2.The substrate temperature of the oCVD process is a crucial process parameter for controlling electrical conductivity and conjugation length. Moreover, the surface morphology is also systemically tunable through variations in substrate temperature, a unique advantage of the oCVD process. By increasing the substrate temperature, the surface morphology becomes more porous, with the textured structure on the nanometer scale. The size of nanopores and fibrils appears uniformly over 25 mm X 25 mm areas on the Si wafer substrates. Conformal coverage of PEDOT films grown with the CuCl2 oxidant (C-PEDOT) is observed on both standard trench structures with high aspect ratio and fragile surfaces with complex topology, such as paper, results which are extremely difficult to achieve with liquid phase based processes. The tunable nanoporosity and its conformal coverage on various complex geometries are highly desirable for many device applications requiring controlled, high interfacial area, such as supercapacitors, Li ion battery electrodes, and sensors. For example, a highly hydrophilic surface with the static water contact angle down to less than 10 degrees is obtained solely by changing surface morphology. By applying fluorinated polymer film onto the nanoporous C-PEDOT via initiative chemical vapor deposition (iCVD), the C-PEDOT surface also shows the contact angle big her than 150 degrees. The hierarchical porous structure of fluorinated polymer coated C-PEDOT on a paper mat shows superhydrophobicity and oil repellency.