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Determination of quasi-fermi level separations in quantum well solar cells


Research objectives and content
The quantum well solar cell is a novel device in which quantum wells (QWs) are used to enhance the efficiency of photovoltaic (PV) cells. QWs are ultra thin layers of low band-gap material, produced by modern epitaxial growth techniques, which have been extensively studied for lasers and other opto-electronic devices. The Imperial College group were the first to demonstrate that QWs enhance the short-circuit current and power conversion efficiency of p-i-n solar cells compared to control cells without wells. There has, however, been controversy concerning the output voltage QW cells might attain. This is determined, fundamentally, by the quasi-Fermi level separation (AEf). The aim of this project is to determine AEf quantitatively in multi-quantum well solar cells. The research will extend the work done in the Imperial College group by myself on my Diploma project while still a University of Karlsruhe undergraduate. The method is to measure the electroluminescence (EL) i.e. the light output from the cells in the dark, as a function of bias and temperature. The light output is calibrated in absolute units by measuring the photocurrent from a known laser excitation, and the bias and temperature dependence is modelled in terms of AEf. The calibration of the EL signal in absolute units is one of the innovative features of this project. The JOULE-THERMIE workprogramme recognises that "solar PV is among the most promising renewable technologies for long term energy supply..." The quantitative determination of AEf is of fundamental importance for all types of solar cells, not just QW cells or those made from III-V materials Training content (objective, benefit and expected impact)
The research project will be directed towards the award of a Ph.D. The Experimental Solid State Physics Group organises an M.Sc. in Semiconductor Science and Technology. I will take the M.Sc. courses will in the first year which will provide an ideal theoretical background for the project. The research experience, originality of the project and the organisational experience to be gained by collaborating with the group, Interdisciplinary Research Centre, industry and researchers in other U.K. universities and abroad will provide training which should result in the award of an excellent Ph.D. degree.
Links with industry / industrial relevance (22)
The group has very good links to EEV, a major European manufacturer of GaAs space solar cells grown by MOVPE. QWs can be added during MOVPE growth with no extra cost. BP Solar, the largest manufacturer of PV cells and modules in Europe, strongly supported the group's recent application to the U.K. PV Technologies initiative. The research is relevant to many other QW devices being developed by European IT industry.


Imperial College of Science, Technology and Medicine
Blackett Laboratory Prince Consort Road
SW7 2BZ London
United Kingdom

Participants (1)

Not available