Enhanced Optical Property with Tunable Band Gap of Cross‐linked PEDOT Copolymers via Oxidative Chemical Vapor Deposition

Abstract

85wileyonlinelibrary.com been attracted by polymers based-on polyacetylene, [ 2,3 ] polypyrrole, [ 4 ] polythiophene, [ 2,5 ] polyphenylene, [ 2 ] polyphenylene-vinylene, [ 2 ] polyaniline [ 6 ] and poly(3,4-ethylenedioxythiophene) (PEDOT), [ 3,7 ] and their derivatives. Table 1 summarizes [2][3][4][5][6][7][8] the characteristics of these polymers: the band gap, electrical conductivity, dopant counterion, and chemical structure. This class of materials has been extensively implemented as electrodes, electrical conductors (e.g., charge carrier transport layers) and semiconducting active layers in many organic electronic and optoelectronic devices that include lightemitting diodes, [ 9 ] fi eld effect transistors [ 10 ] and photovoltaic cells. [11][12][13] These devices have successfully demonstrated high device performance comparable to classical Si-or oxide-based technologies. Polymers based on PEDOT [ 3,14 ] are of particular interest due to their high electrical conductivity, mechanical fl exibility, as well as their stability relative to other conjugated polymers.Oxidative chemical vapor deposition (oCVD) offers a facile approach to synthesize and deposit conjugated polymers irrespective of polymer solubility or the properties of the substrate material. The oCVD method has the merits of good fi lm uniformity [ 7,15 ] over the large areas, high electrical conductivity, [ 15 ] conformal coating on non-planar [ 12,13 ] (e.g., textiles and papers) and patterned [ 16,17 ] (e.g., trench) substrates, and relatively low process temperature [ 15,17 ] (25-150 °C). Previously, we reported on the oCVD synthesis of conjugated homopolymer thin fi lms of the doped conducting polymer PEDOT [ 15,17 ] with systematically tunable band gap over ≈0.3 eV [ 14 ] and excellent adhesion to the substrate through grafting. [ 18 ] The oCVD platform has been demonstrated for the dedoped semiconducting homopolymers polythiophene, [ 19,20 ] polyisothianaphthene, [ 21 ] and polyselenophene. [ 22 ] The oCVD synthesis method has also achieved copolymers from thiophene-3-acetic acid with EDOT [ 23 ] and with pyrrole. [ 24 ] Additionally, 3-thiopheneethanol (3-TE) has been oCVD copolymerized with EDOT. [ 25 ] The oCVD fi lms fi nd application including transparent conductors for electrodes [ 13 ] and carrier transport layers, [ 26 ] sensors [ 23,25,27 ] and electrochromic devices. [ 28 ] Highoptical transmittance conjugated-polymers with electrical conductivity are garnering much attention for the applications in organic optoelectronic devices including organic fi eld-effect-transistors and solar cells. Polymers based on PEDOT are particularly promising candidates with high conductivity, uniform surface planarity and excellent ductility. In this work, homopolymer PEDOT deposited using oxidative chemical-vapordeposition(oCVD) show the maximum conductivity of ≈3500 S/cm. However, their utility is limited due to the relatively low transmittance and abrupt decrease near the red edge in the visible regime. Here, the signifi cantly improved opti...

Device Fabrication Based on Oxidative Chemical Vapor Deposition (oCVD) Synthesis of Conducting Polymers and Related Conjugated Organic Materials

“…Utilizing a modified reactor configuration, monomers which are solids at ambient conditions have also been successfully oCVD polymerized including 3,4‐propylene dioxythiophene, 2,2‐dimethyl‐3,4‐propylene dioxythiophene, 2,2′‐bithiophene, 3,2′:5′3″‐terthiophene, and thieno[3,2‐ b ]thiophene. The oCVD copolymerization of EDOT with the solid monomers anthracene or biphenyl produced systematic bandgap tuning . The low‐bandgap semiconductor 1,3‐dihydroisothianaphthene (DHITN) has been demonstrated with a modified oCVD process.…”

“…The introduction of oxidants (especially solid ones) through the vapor phase to the oCVD reactor is more challenging than vapor delivery of the monomers since many solid oxidants have low volatility. The most common oxidant used for oCVD to date is iron chloride (FeCl 3 ) . A tall reactor is often used for sublimating the solid oxidants like FeCl 3 inside the oCVD vacuum chamber.…”

In-Situ Approaches for the Preparation of Polythiophene-Derivative Cellulose Composites with High Flexibility and Conductivity

“…There are no substantial differences in the spectra obtained of cellulose fibers and Whatman filter paper substrates, identifying the most intense band in the region between 1180 and 940 cm −1 attributed to C-O and C-C stretching vibrations [31,32]. PEDOT-cellulose materials present FTIR peaks at 1518, 1350, and 1220 cm −1 that can be attributed to the quinoid structure and stretching modes of C=C and C-C in the thiophene ring and the stretching of the C-O-C bond in the ethylendioxy group of PEDOT, which demonstrates that PEDOT was successfully coated on the cellulose fibers in all composites materials prepared [33,34]. Other characteristic peaks can be found at around 980, 830, and 695 cm −1 due to the vibration modes of the C-S bond in the thiophene ring [35].…”

Synthesis of coaxial nanotubes of polyaniline and poly(hydroxyethyl methacrylate) by oxidative/initiated chemical vapor deposition

“…The oCVD technique is based on step-growth polymerization where the polymerization takes place directly on the surface of the substrate. The oxidant, either liquid [37] or solid [38], and the monomers are delivered into the vacuum system simultaneously, initiating the polymerization reaction on the surface. The key advantages of oCVD are good homogeneity, retention of polymer functional groups due to low reaction temperature (25–100 °C), adequate electrical conductivity for a wide range of applications and high-quality conformal CP thin films on various non-planar surfaces [39–41].…”