| EPSRC Reference: |
EP/F008589/1 |
| Title: |
Proof of Concept for enhancing single-junction and tandem concentrator cells by photon recycling |
| Principal Investigator: |
Barnham, Professor K |
| Other Investigators: |
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| Researcher Co-Investigators: |
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| Project Partners: |
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| Department: |
Physics |
| Organisation: |
Imperial College London |
| Scheme: |
Follow on Fund |
| Starts: |
01 August 2007 |
Ends: |
31 July 2008 |
Value (£): |
70,003
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| EPSRC Research Topic Classifications: |
| Materials Characterisation |
Materials Processing |
| Materials Synthesis & Growth |
Solar Technology |
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| EPSRC Industrial Sector Classifications: |
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| Related Grants: |
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| Panel History: |
| Panel Date | Panel Name | Outcome |
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03 Apr 2007
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Follow on Fund 4
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Announced
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Summary on Grant Application Form |
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This proposal concerns a novel type of photovoltaic (PV) solar cell. The threat of global warming is one reason for the rapid expansion in this low-carbon technology. In recent years, world-wide, solar cell manufacturing has been increasing exponentially by 47% each year. The development of higher efficiency cells will help this expansion continue. The Imperial Quantum Photovoltaic Group (QPV) have been collaborating with the EPSRC National Centre for III-V Technologies on an EPSRC grant GR/S81933 which has developed a novel, nano-structured solar cell known as the strain-balanced quantum well solar cell (SB-QWSC). Their primary achievement was to demonstrate a cell which operates at a 27% efficiency which is approximately twice the efficiency of the current Si based PV cells and close to the single junction cell efficiency record of 27.8%. The SB-QWSC is made from GaAs based alloys using the quantum well (QW) technology which underpins modern communication devices such as the laser, LED and the amplifier in mobile phones. The rapid PV market expansion has lead to a silicon feed-stock shortage, so cells based on a different material system and production technology are important if the expansion is to be maintained. As GaAs based cells are expensive a number of companies are developing light-concentrating systems, in which lenses or mirrors focus sunlight onto the cells. This way it is possible to reduce the area of the expensive PV cell by about 1/500. This leads to a major price reduction. The QWs give the cell a wider spectral range without introducing crystal dislocations. Both features give the SB-QWSC a number of advantages in concentrator applications over the tandem or triple junction GaAs based cells which were designed for use in space. The absence of dislocations means the SB-QWSC will have a longer device lifetime than the highest efficiency version of the multi-junction cell. At the same efficiency a SB-QWSC will outperform a conventional tandem cell because it does not require a tunnel junction to connect the cells. The wider spectral range of the QW cell results in significantly more electrical energy being harvested over a year due to the seasonal and daily spectral variation of the sunlight. The QPV group have also demonstrated that when the SB-QWSC is incorporated in a tandem cell the wider spectral range leads to a higher cell efficiency. This enhancement is such that in Madrid, where there is a guaranteed price for PV electricity fed into the grid, the energy savings are as large as the system capital cost over the anticipated 25 year lifetime. In the course of project GR/S81933 the QPV group unexpectedly observed that the SB-QWSC was exhibiting a phenomenon known as photon recycling when operating at high concentration. They had already demonstrated that the quantum well material was of such good quality that the only loss mechanism which operates at high light levels was the unavoidable loss of the current carriers back into photons of light. They observed that, when a mirror, known as a distributed Bragg reflector (DBR) is grown under the quantum wells, some of these lost photons are reflected back into the QWs. Here they are absorbed like the incident sunlight, add to the current and enhance the efficiency. The aim of this project is to study this effect further and see if it can be exploited commercially. We will investigate the use of deeper QWs, different DBRs and transparent substrates to maximise the effect in both single-junction and tandem cells. The maximum efficiency gain which might be achieved is ~ 4%, which is similar to that discussed above, i.e. giving savings similar to the system cost in a sunny location with a guaranteed price for PV electricity. This project should provide very significant added value to the second generation products of or our new company QuantaSol and also strengthen the intellectual property.
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Key Findings |
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This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
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Potential use in non-academic contexts |
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This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
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Impacts |
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| Description |
This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk |
| Summary |
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| Date Materialised |
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Sectors submitted by the Researcher |
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This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
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| Project URL: |
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| Further Information: |
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| Organisation Website: |
http://www.imperial.ac.uk |