Surface and bulk phenomena in conjugated polymers devices

We report a number of investigations into a variety of surface and bulk phenomena which are particularly relevant to the design of polymer optoelectronic devices, and in particular to light-emitting diodes (LEDs). First, we consider the surface properties of the most common anode, a thin layer of indium tin oxide (ITO), as modified by chemical and physical treatments. We show how the treatments affect the electrode workfunction, surface energy, morphology, sheet resistance and therefore, the LEDs efficiency and lifetime. We will also consider the effect of a conducting polymer hole-transport layer, such as poly(styrene sulfonate) doped poly(3,4-ethylene dioxythiophene) (PEDOT), incorporated between the ITO and the active layer. Secondly, we turn our attention to the optimisation of the photoluminescence (PL) efficiency, and report examples of how the polymer microstructure and possibly the engineering of disorder in a class of poly( p-phenylene vinylene)s and poly- or oligo-thiophenes can determine a significant increase of the PL efficiencies in the solid state. (C) 2000 Elsevier Science S.A. All rights reserved.