Conjugated polymer surfaces and interfaces

Abstract

The doping of a conjugated polymer, polyacetylene, to a state of high electrical conductivity in 1977 marked a distinct step in interest in the electronic and transport properties of electrically conducting organic materials. Since 1990, however, undoped semiconducting conjugated polymers have emerged as potentially useful electronic materials in a variety of electronic and optoelectronic applications. In the context of polymer–based electronic device applications, it is of critical importance to understand the nature of the electronic structure of the polymer surface and the polymer–metal interface. It has been shown that, especially for conjugated polymers, photoelectron spectroscopy provides a maximum amount of both chemical and electronic structural information within a single measurement technique. This contribution contains an overview of some details of the early stages of interface formation with metals on the surfaces of conjugated polymers and model molecular solids, as studied using photoelectron spectroscopy. The materials chosen are especially of interest in connection with polymer-based light emitting devices, or LEDs. Specifically, the materials involved include poly( p –phenylenevinylene), or PPV, and a series of substituted PPVs, as well as a diphenylpolyene molecule for PPV, namely, α,ω–diphenyltetradecaheptaene. Some general trends in the behaviour of light–metal atoms on the clean surfaces of conjugated polymers are pointed out. Some consequences, based upon the information obtained in the studies reviewed, are highlighted. Finally, two recent issues, which are studied by the methods used for the metal–on–polymer interfaces studies, are covered: the role of water vapour on the electronic structure of PPV; and the use of phase–separated polymer blends to increase the quantum efficiency of blue light emitting diodes.