Alkoxysulfonate-Functionalized PEDOT Polyelectrolyte Multilayer Films:  Electrochromic and Hole Transport Materials

Water-soluble poly(4-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl-methoxy)-1-butanesulfonic acid (PEDOT-S) has been synthesized both chemically and electrochemically, and the properties of the resultant films have been examined and compared. In particular, it was found that PEDOT-S, deposited in conjunction with poly(allylamine hyrochloride) PAH in the form of polyelectrolyte multilayer (L-B-L) films of PEDOTS/PAH, possesses highly advantageous properties that allow for applications involving aqueous-based electrolytes. Electrochemically prepared films of PEDOT-S and L-B-L prepared films of PEDOT-S/PAH were characterized by electrochemical, spectroelectrochemical, and colorimetric methods illustrating reversible redox states at −0.2 and +0.2 V, respectively (vs Ag/Ag+ in organic media), which resulted in distinctive color changes between light blue (oxidized) and purple/pink (neutral). The change in color states was evident by a change in the electronic absorbance in the 500 nm region (neutral state) which was transferred to the near-IR absorption >800 nm (oxidized state). The phenomena of “acid doping” in aqueous and organic media was also investigated spectroscopically and found to result in a reversible color change accompanied by a relatively small changes in conductivity between 2 × 10-4 S/cm (oxidized) and 7.1 × 10-5 S/cm (neutral) when films were deposited on glass. In all cases, PEDOT-S/PAH exhibited superior and more reproducible electrochemical properties relative to electrochemically formed films that were tested for possible application in electrochromic devices and as the hole transport layer of OLEDs. It was found that PEDOT-S/PAH displays comparable properties to spin-coated PEDOT:PSS as a hole injecting layer in NIR emitting PLEDs.