Synthesis and device characterisation of side-chain polymer electron transport materials for organic semiconductor applications

Improved syntheses and polymerisations are reported of monomers bearing electron transporting substituents based on 2,5-diphenyloxadiazole and 2,3-diphenylquinoxaline attached directly to a vinyl group. By copolymerisation and by use of mixtures of homopolymers, these materials have been incorporated into light emitting polymer devices in which hole conduction properties are provided by 4-vinyltriphenylamine groups. High luminescence efficiency is achieved by use of a fluorescent additive. The resulting devices show narrow emission bands and high brightnesses, except in the case of those based on a diphenyloxadiazole–triphenylamine polymer blend. Thermal analysis data are equivocal but we present evidence that in this system, but not the quinoxaline blend, phase separation occurs. The minority charge carrying capacity of the homopolymers is probed: it is shown that the quinoxaline derivative has hole blocking properties superior to those of the oxadiazole polymer and is a good candidate for use in optimised devices.