ABSTRACT
Carbazole and triphenylamine derivatives are good hole transport materials in solid state. Driven by an applied external electrical potential, positive charges are injected from the electrode and migrate effectively in the solid matrix. In solution, on the other hand, carbazole and triphenylamine cations tend to dimerize, oligomerize, or polymerize. In the present chapter, some fundamental properties about the chemical reactivity of carbazole and triphenylamine derivatives toward electropolymerization are reviewed. 9.1 Introduction
Polymeric optoelectronic devices derived from conjugated polymers or nonconjugated materials have become extremely important areas
of study due to their advantages of the high mechanical strength as well as homogeneous coating technologies [1-10]. To fabricate thin-film organic electronic devices, polymeric materials are usually coated as uniform thin films directly on an electrode by spincasting and dip-coating [11], contact printing [12], or roll-to-roll printing methods [13]. This requires good solubility of the polymers in an appropriate solvent. Due to the low solubility of conjugated polymers, their optoelectronic applications are sometimes limited. To enhance the solubility of the conjugated polymers, alkyl or alkoxyl side chains have to be introduced [14-16]. This leads to a dilemma in designing materials for polymeric devices: First, this might create some other difficulties for fabrication of the multilayer device structures. For examples, swelling or redissolution of the precoated layers, due to their good solubility, from substrate may occur during the sequential coating process, and thus lead to destruction of the device structures. Direct film formation on ITO glass by chemical cross-linking [17], thermal treatment [18], selfassembly methods [19,20], or electropolymerization [21] provides options to bypass the solubility problem. The second challenge is due to the difficulties involved in formulating optoelectronic polymers with photolithographic-compatible properties. This problem has been partially solved by direct deposition methods, such as ink jet printing [22] and screen printing [23,24], or by diffusing color dyes [25-28] in light-emitting backplanes.
