LIGHT-EMITTING AND PHOTOCONDUCTIVE DIODES FABRICATED WITH CONJUGATED POLYMERS

Processible conjugated polymers can be used to fabricate a range of th in-film diodes which can be designed to show good characteristics both as electroluminescent diodes and also as photoconductive diodes. We c onsider the present understanding of the operation of light-emitting d iodes which use conjugated polymers for both charge transport and emis sion. We highlight the improvement to the electroluminescence efficien cy that can be produced by the use of two polymer layers selected so t hat the heterojunction between the two layers is able to confine charg e and thus bring about electron-hole capture to generate excitons at t his interface. Photon absorption produces excitons which are considere d to be bound at room temperature. Charge penetration requires ionisat ion of these excitons, which can be achieved efficiently at heterojunc tions between layers with different electronegativities, and we report how this can be achieved at the interfaces between interpenetrating n etworks of electron- and hole-accepting polymers.