Oxidative Chemical Vapor Deposition of Electrically Conducting Poly(3,4-ethylenedioxythiophene) Films

Abstract

An oxidative chemical vapor deposition (CVD) process is presented as an alternative to conventional solution-based processing of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films. This solventless technique yields PEDOT with higher conductivities and conformally coats fibers and other high area morphologies, important for enhancing efficiencies in some organic electronic devices. The CVD method eliminates corrosive poly(styrenesulfonate) that is used to disperse PEDOT in an aqueous suspension for solution-based processing. A mechanistic approach is presented that favors the deposition of the conjugated, conducting form of PEDOT. We achieved conductivities as high as 105 S/cm and demonstrated films about 100 nm thick that do not crack upon bending and are more than 84% transparent to visible light. The compatibility of oxidative CVD deposition of PEDOT is demonstrated on silicon, glass, plastic, and paper substrates.

Effect of Imidazole and Surfactant on the Opto-Electrical Properties of PEDOT Thin Films via Vapor Phase Polymerization

“…[19][20][21] Various non-conductive materials such as glass and poly(ethylene terephthalate) (PET) can be used as coating substrates. 20 The typical oxidants used in the VPP of PEDOT are iron(III)-based halides 19 or salts such as ferric p-toluenesulfonate (FTS).…”

“…[19][20][21] Various non-conductive materials such as glass and poly(ethylene terephthalate) (PET) can be used as coating substrates. 20 The typical oxidants used in the VPP of PEDOT are iron(III)-based halides 19 or salts such as ferric p-toluenesulfonate (FTS). [22][23][24] Contemporary research on PEDOT thin films has predominantly focused on testing various additives in the FTS solution to improve the electrical conductivity of the conductive films.…”

“…13 An abundance of methods have been described for the production of PEDOT-based thin films using various synthesis techniques, including electrochemical synthesis, 14 liquid-phase polymerization (LPP), 15 micellar polymerization, 16 and vapor-phase polymerization (VPP). [17][18][19] Recently, VPP has drawn close consideration as a means for the in situ synthesis of PEDOT thin films on variously shaped substrates, due to its ability to overcome issues associated with film processing/coating, performance, and pot-life. Through † To whom correspondence should be addressed.…”

Vapor phase oxidative synthesis of conjugated polymers and applications

“…55 This solventless deposition technique yielded PEDOT films with conductivities as high as 105 S cm À1 and 84% transparency. Later, surface roughness of the deposited PEDOT was significantly improved by modifying the oCVD reactor configuration.…”

“…29 Too strong or too acidic nature of an oxidizing agent can sometimes over oxidize the growing polymer, which results in disruption in conjugation and reduced electrical conductivity. 55,82 Organic bases, such as pyridine and imidazole, are known to reduce the acidity of the oxidants, lower the rate of polymerization, and increase the electrical conductivity of the deposited polymers. 55,82 In addition to controlling the humidity in the VPP chamber, incorporation of a surfactant such as poly(ethylene glycol)-ran-poly(propylene glycol) (PEG-ran-PPG) to the oxidant solution also inhibits the adverse effects of water absorption and prevents the oxidant from forming crystallite domains during the VPP process resulting in a significant increase in the conductivity from 84 S cm À1 to 528 S cm À1 .…”