This thesis focuses on the electronic and photophysical phenomena that occur at the heterojunction between two distinct organic semiconductor materials. The hetero junction luminescence is correlated to the photovoltaic performance in a polymer blend diode. Polymer semiconductor blends allow efficient operation of photovoltaic diodes when there is a large interfacial area of hetero junction between electron donor and acceptor polymers. In this thesis, we use electromodulation spectroscopy to investigate the luminescent and photovoltaic behaviour of electron- and hole-transporting polyfluorenes blends at a broad range of blend ratios, temperatures and electric fields. In the systems investigated, an exciton at the hetero junction produces either free charges or an exciplex (or a similar interfacially-bound charge-transfer pair). We find that an externally-applied electric field increases the number of free charges and quenches the exciplex luminescence with a one-to-one correspondence: the increase of the photocurrent internal quantum efficiency is equal to the reduction in the exciplex emission. We conclude that, independent of temperature and morphology, the photovoltaic quantum yield is predominantly limited by the dissociation of the geminate electron-hole pair intermediate at the hetero junction. Once the charges are fully separated they are transported across the material and collected at the external circuit with nearly unit efficiency.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:599488 |
| Date | January 2008 |
| Creators | Gonzalez-Rabade, A. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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