Semiconductor device physics 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 consider here the present understanding of the operation of a range of semiconductor devices. Field-effect transistors are readily fabricated but are limited by low carrier mobilities. However, these can be improved by ordering the polymer films. For light-emitting diodes 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. Photon absorption produces excitons which are considered to be bound at room temperature. Charge generation requires ionisation of these excitons, which can be achieved efficiently at heterojunctions between layers with different electronegativities, and we discuss how this can be achieved at the interfaces between interpenetrating networks of electron- and hole-accepting polymers.