The Molecular Structure of PEDOT

1 Doping in Poiy(p-Phenyiene Vinyiene) and Poiy(3,4-Ethyienedioxythiophene) 

Regarding the nature of the excited states that are created when photons are absorbed, the experimental results are presented in Fig. 3.3. The figure shows absorption spectra in the Vis range, which were obtained for a series of oligomers of poly(p-phenylene vinyiene) (PPV). The four presented absorption bands all have a similarly fine structure and are shifted against each other the higher the number of monomers, the lower the frequency. A first conclusion can be drawn from the invariance of the profile of the bands. Since it is independent of the number of coupled monomers it must be a property of the monomer itself 

The conjugation, that is, the resonance interaction between the n bonds, results in delocalized n electron states. In the case of PPV these states are occupied by the eight n electrons. There is a highest occupied molecular n orbital, and there is a gap by extending up to next level, the lowest unoccupied molecular n orbital. 

Electrochemical doping The doping charge comes from the electrode and the ions of the salt included in the electrochemical bath play the role of the counterions (Fig 3.6). 

Chemical doping The doping charge (electron or hole) on the conjugated molecules or polymers comes from another chemical species (atom or molecule). The chemical species become the counterions of the polarons created on the conjugated materials. 

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The first conducting polymer was trans-polyacetylene which was doped with bromine and was produced at 1970s. Soon other conjugated polymers such as poly (p-phenylene), polypyrrole (PPy), polyethylene dioxythiophene (PEDOT) and polyaniline (PANi) and their derivatives which are stable and processable were synthesized. The molecular structures of a few ICPs are shown in Figurel. 

FIGURE 3.1 The molecular structure of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT-PSS). 

FIGURE 1.2. Molecular structure of widely used it-conjugated and other polymers (a) poly(para-phenylene vinylene) (PPV) (b) a (solid line along backbone) and it ( clouds above and below the a line) electron probability densities in PPV (c) poly(2-methoxy-5-(2 -ethyl)-hexoxy-l,4-phenylene vinylene) (MEH-PPV) (d) polyaniline (PANI) (d.l) leucoemeraldine base (LEB), (d.2) emeraldine base (EB), (d.3) pernigraniline base (PNB) (e) poly(3,4-ethylene dioxy-2,4-thiophene)-polystyrene sulfonate (PEDOT-PSS) (f) poly(IV-vinyl carbazole) (PVK) (g) poly(methyl methacrylate) (PMMA) (h) methyl-bridged ladder-type poly(jf-phenylene) (m-LPPP) (i) poly(3-alkyl thiophenes) (P3ATs) (j) polyfluorenes (PFOs) (k) diphenyl-substituted frares -polyacetylenes (f-(CH)x) or poly (diphenyl acetylene) (PDPA). 

Tables 6-9 give the device structures and performance metrics for monochromatic OLEDs that utilize organometallic emitters. Eigures 38-42 show the molecular structures for the various materials used in these devices. White OLEDs have also been prepared with these materials, but these will be discussed in a later section. Light-emitting electrochemical cells are treated in a separate section as well, since the finished devices have different operating characteristics than either of the other solution or vapor processed devices. Table 6 lists devices made solely with discrete molecular materials, while Table 7 gives data for devices made using polymeric materials. The only exception to the use of discrete molecular materials in Table 6 is for devices that use a conducting polymer, poly(3,4-ethylenedioxythiophene polystyrene sulfonate) (PEDOT), as a material to enhance the efficiency for hole injection into the organic layer. The mode of preparation for a given device is listed with the device parameters in the...

Fig. 6.13 Molecular structures of the donor and acceptor constituting the emitting layer in a PhOLED, ITO/rubbed PEDOT PSS (30 nm)/(38) (39) at 3 1 mass ratio (55 nm)/TPBi (45 nm)/ LiF (0.5 nm)/Al (150 nm) with its linearly polarized electroluminescence spectra. Used with permission [50]...

Poly(3,4-ethylenedioxythiophene) (PEDOT) is formed from polymerization of bi-cyclic monomer 3,4-ethylenedioxythiophene (EDOT). The structure of PEDOT is shown in Eig. 3. Due to its narrow energy gap of the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) [59, 68],... 

Kanatzidis has recently prepared the thio analogue to PEDOT, namely poly(3,4-ethylenedithiathiophene) [192] by the FeCl method. Unfortunately the molecular weight of the polymer was found to be around 3-4K and the solubility was a bit low. However, this exceptionally interesting structure exhibited conductivities of around 0.4Scm and very interesting thermopower behavior reminiscent of a metallic state. 

With molecular structures similar to the MEH-PPV CN-PPV system, the intensively studied M3EH-PPV CN-ether-PPV system—either as a blend or as a bilayer—resulted more recently in higher efficiencies under full AM 1.5 illumination (lOOmW/cm ) (Fig. 46) [35,223-225]. The first blend devices incorporated either a flat sintered titanium dioxide (Ti02) or a PEDOT PSS interlayer at the ITO interface. Blend devices with PEDOTiPSS and Ca electrodes led to power conversion efficiencies of 1% and EQEs of up to 23%. 

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