Light-emitting diodes fabricated with conjugated polymers

Processible conjugated polymers can be used to fabricate a range of thin-film diodes which can be designed to show good characteristics, both as electroluminescent diodes and also as photoconductive diodes. We discuss the present understanding of the operation of light-emitting diodes which use conjugated polymers for both charge transport and emission. We highlight the improvement to the electroluminescence efficiency that can be produced by the use of two polymer layers selected so that the heterojunction between the two layers is able to confine charge and thus, bring about electron-hole capture to generate excitons at this interface. The nature of these diodes allows fabrication of microcavity structures in which the emission characteristics of the polymer are strongly modified by the allowed cavity modes. This can be used to control the colour of emission and sharpness of the emission bands.