The anisotropic conductivity of thin films of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is correlated to the film morphology as obtained from scanning tunneling and atomic force microscopy images. The material was found to consist of layers of flattened PEDOT‐rich particles that are separated by quasi‐continuous PSS lamella (see figure).

Poly (3,4-ethylenedioxythiophene) : poly(styrenesulphonic acid) (PEDOT : PSS) is commonly used as an anode in polymer light-emitting diodes (PLED). We have studied the effect of the pH and Na + ion concentration of the aqueous PEDOT : PSS dispersion on the bulk and surface properties of spincoated films by various techniques, including UV-vis-NIR optical absorbance spectrometry, Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoemission Spectroscopy (UPS). A pH increase by addition of NaOH modifies the PEDOT : PSS properties in a similar way as electrochemical dedoping: the IR absorbance decreases, the Raman peaks shift, sharpen and increase in intensity, and the work function decreases. Consequently, a barrier for hole injection is introduced for several classes of light-emitting polymers. We argue that the mechanism of the pH-effect is different from electrochemical dedoping, and originates from a change in the relative stability of polarons and bipolarons on the doped thiophene. The changes in the electronic properties of PEDOT : PSS point to the determining role of the counter-ion in the stabilisation of oxidised thiophene units. Polymer LEDs comprising Na + -rich, proton poor PEDOT : PSS can show lower lifetime and efficiency than the corresponding Na + -free, proton-rich devices. For light emitting polymers which suffer from the addition of sodium to the hole injecting PEDOT : PSS, the decreased lifetime hints at hole injection as limiting factor in the degradation of these PLEDs.

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The prerequisites for the polymerization process of sulfinyl monomers toward precursor polymers for poly(p-phenylenevinylene) were investigated. In this process, proton abstraction affords the premonomer anion, which is converted to the actual monomer, viz. a p-xylylene derivative. These p-xylylene derivatives polymerize spontaneously without external initiation. In hydrogen bond donor solvents (HBD solvents) like alcohols, three products can be isolated. High molecular weight polymer is formed together with a residual fraction that consists of a minor amount of premonomer and a large amount of solventsubstituted product. These solvent-substituted products are most likely formed by addition of a solvent anion to the actual monomer and cannot participate in the polymerization process anymore. Solvent substitution is therefore an important side reaction and has to be avoided. It was found that, in branched alcohols such as s-butanol, conversion of premonomer to actual monomer is very efficient, resulting in a rapid buildup of p-xylylene derivative. In this way the polymer yield was increased to 90%.