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

Improved syntheses and polymerisations are reported of monomers bearing ele ctron transporting substituents based on 2,5-diphenyloxadiazole and 2,3-dip henylquinoxaline attached directly to a vinyl group. By copolymerisation an d by use of mixtures of homopolymers, these materials have been incorporate d into light emitting polymer devices in which hole conduction properties a re provided by 4-vinyltriphenylamine group,High luminescence efficiency is achieved by use of a fluorescent additive. The resulting devices show narro w emission bands and high brightnesses, except in the case of those based o n a diphenyloxadiazole-triphenylamine polymer blend. Thermal analysis data are equivocal but we present evidence that in this system, but not the quin oxaline blend, phase separation occurs. The minority charge carrying capaci ty of the homopolymers is probed: it is shown that the quinoxaline derivati ve has hole blocking properties superior to those, of the oxadiazole polyme r and is a good candidate for use in optimised devices.