Reactive Vapor Deposition of Conjugated Polymer Films on Arbitrary Substrates

Summary

This paper presents a protocol for reactive vapor deposition of poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), and poly(thieno[3,2-b]thiophene) films on glass slides and rough substrates, such as textiles and paper.

Abstract

We demonstrate a method of conformally coating conjugated polymers on arbitrary substrates using a custom-designed, low-pressure reaction chamber. Conductive polymers, poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-propylenedioxythiophene) (PProDOT), and a semiconducting polymer, poly(thieno[3,2-b]thiophene) (PTT), were deposited on unconventional highly-disordered and textured substrates with high surface areas, such as paper, towels and fabrics. This reported deposition chamber is an improvement of previous vapor reactors because our system can accommodate both volatile and nonvolatile monomers, such as 3,4-propylenedioxythiophene and thieno[3,2-b]thiophene. Utilization of both solid and liquid oxidants are also demonstrated. One limitation of this method is that it lacks sophisticated in situ thickness monitors. Polymer coatings made by the commonly used solution-based coating methods, such as spin-coating and surface grafting, are often not uniform or susceptible to mechanical degradation. This reported vapor phase deposition method overcomes those drawbacks and is a strong alternative to common solution-based coating methods. Notably, polymer films coated by the reported method are uniform and conformal on rough surfaces, even at a micrometer scale. This feature allows for future application of vapor deposited polymers in electronics devices on flexible and highly textured substrates.

Introduction

Polymeric conducting and semiconducting materials have unique properties, such as flexibility¹, stretchability², transparency³, and low density,⁴ which provide extraordinary opportunities for creating next-generation electronic devices on nontraditional substrates. Currently, many researchers are endeavoring to take advantage of the unique properties of polymeric materials to create flexible and/or wearable electronics^5,6 and smart textiles⁷. However, the ability to conformally coat highly te....

Protocol

Read MSDS for reagents and follow all chemical safety measures as required by your institution.

1. Deposition of Cl-PProDOT and Cl-PTT

1. Build the structure of the custom-built tubular vapor deposition chamber as shown in Figure 1.
   1. Make a 1/4-in. (outer diameter, O.D.) fused quartz side inlet to a 2-in. (O.D.) fused quartz tube. Make a cold trap with a custom-built U-shape 1-in. stainless-steel tube and a Dewar flask.
   2. Connect the quartz tube with a vacuum gauge and cold trap using stainless-steel KF connectors and quick-connect couplings. Place the monomer in a quartz ampule and....

Results

The thickness of Cl-PProDOT films formed on 1.3 cm x 2.5 cm glass slides placed at discrete lateral positions along the central tube were measured by a profilometer (Figure 3). Conductivities were calculated from resistivity measurements using a home-built four-point probe test station. The measured conductivity of a 100-nm thick Cl-PProDOT film on glass slides is 106 S/cm, which is sufficient to qualify this film as a potential electrode material.

Discussion

The mechanism of the reaction is oxidative polymerization. Polymer coating methods using the same mechanism include electropolymerization¹⁷ and vapor phase polymerization¹⁸. Electropolymerization requires a conductive substrate, lacks the advantage of uniform and conformal coating, and is an environmentally-unfriendly solution-based method¹⁹. The existing vapor phase polymerization method is similar to the method reported here but can only polymerize.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
3,4-Ethylenedioxythiophene, 97%	Sigma Aldrich	483028
3,4-Propylenedioxythiophene, 97%	Sigma Aldrich	660485
Thieno[3,2-b]thiophene, 95%	Sigma Aldrich	702668
FeCl3, 97%	Sigma Aldrich	157740
Br2	Sigma Aldrich	207888