Polyethylenedioxythiophene

A thin layer deposited between the electrode and the charge transport material can be used to modify the injection process. Some of these arc (relatively poor) conductors and should be viewed as electrode materials in their own right, for example the polymers polyaniline (PAni) [81-83] and polyethylenedioxythiophene (PEDT or PEDOT) [83, 841 heavily doped with anions to be intrinsically conducting. They have work functions of approximately 5.0 cV [75] and therefore are used as anode materials, typically on top of 1TO, which is present to provide lateral conductivity. Thin layers of transition metal oxide on ITO have also been shown [74J to have better injection properties than ITO itself. Again these materials (oxides of ruthenium, molybdenum or vanadium) have high work functions, but because of their low conductivity cannot be used alone as the electrode. 

At the ITO interface, various conducting polymers have been introduced between the luminescent polymer and the ITO. These include polyaniline56 and polyethylenedioxythiophene (PEDOT) (Fig. 5.13).37 There are several potential benefits from this approach, including the smoothing out of surface features on the ITO which may lead to short-circuits, the possibility of dopants from the con-... 

Recent encouraging results have been reported by Carter et al., who have obtained room temperature lifetimes in excess of 7000 h for encapsulated ITO/PPV/Ca devices at current densities of 60 mA/cm2.37 The polymer used was the PPV copolymer shown in Fig. 5.23, where the conjugation is interrupted by nonconjugated a -acetyloxy-/ -xylylene units. The efficiency of these devices was typically 0.02 lm/W. Devices operating at 80° C had lifetimes in excess of 1100 h. Carter et al., also reported devices based on the same emissive polymer giving efficiencies between 0.5 and 2 lm/W. These devices used a layer of conducting polymer (polyethylenedioxythiophene/polystyrene sulfonate) between the ITO and the PPV, and a sputtered aluminum/lithium alloy as the cathode. The devices... 

Very few CPs are produced in bulk quantities. Polyphenylene sulfide, a member of the third generation of polymers, was produced in bulk quantities many years before CPs were established and its dopability was elucidated. Polyethylenedioxythiophene is commercially available as a water-based colloidal dispersion (Baytron P water dispersion), and presumably as dispersible powders. The powders with a conductivity of 5-10 S/cm can be dispersed in thermoplastic polymers and in organic solvents such as xylene. Polyaniline doped with dodecylbenzene sulfonic acid and complexed with zinc dodecylbenzene sulfonate is commercially available as a powder, which can be dispersed in polyolefins. The same polymer doped with p-toluenesulfonic acid is also available as a dispersible powder, Ormecon, and in a predispersed form for solution processing in polar and nonpolar media. Based on Ormecon PANi, there are many commercial products marketed for many different applications. 

Anothumakkool, B., A. T. A. Torris, S. N. Bhange, M. V. Badiger, and S. KurungoL 2014. Electrodeposited polyethylenedioxythiophene with infiltrated gel electrolyte interface A close contest of an all-solid-state supercapacitor with its liquid-state counterpart. Nano scale 6 5944-5952. 

On the substrate side, the same process occurs for the holes, but on a different energy level. The holes are injected with a high work fimction metal or semiconductor like the transparent indium-tin-oxide ITO, which consists of a nonstoichiometric composite of 10-20% Sn02 and 80-90% ln203. The work function of ITO depends strongly on the surface treatment and lies in the range of 4.4-S.2 eV [43,44]. As in the case of the cathode, hole injection can be improved by an additional layer of, e.g., copper phthalocyanine [45] or polyethylenedioxythiophene (FEDOT), doped with polystyrenesulfonic acid (PSS) [46]. The holes are injected into the hole transport layer and proceed... 

P.-H. Aubert, L. Groenendaal, F. Louwet, L. Lutsen, D. Vanderzande and G. Zotti, In situ conductivity measurements on polyethylenedioxythiophene derivatives with different counterions, Synth. Met. 126, 193-198 (2002). 

Daoud, W.A., Xin, J.H., Szeto, Y.S., 2005. Polyethylenedioxythiophene coatings for humidity, temperature and strain sensing polyamide fibers. Sensors and Actuators B Chemical 109 (2), 329-333. 

F. Jonas and J.T. Morrison, 3,4-Polyethylenedioxythiophene (PEDT) Conductive coatings technical applications and properties. Synthetic Metals, 85(1-3) 1397-1398,1997. 

Cogan SF, Peramunage D, Smirnov A et al (2(X)7) Polyethylenedioxythiophene (PEDOT) coatings for neural stimulation and recording electrodes. Mater Res Soc Meet, (Abstr. QQ2.7), Nov. 26-30, 2007, Boston... 

The polymerization processes described in this chapter may also impart a helical structure in heterocyclic conjugated polymers or aromatic systems that do not have chiral substituents in the side chain. In fact, in recent years various helical conjugated copolymers, such as poly thiophenes, polyethylenedioxythiophenes, and phenylene-thiophene, have been synthesized by electrochemical or chemical polymerization using the N -LC host phase [171-178]. 

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