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Minority carrier lifetime mapping of solar cells

Fisher, Rebbeca (2011) Minority carrier lifetime mapping of solar cells. Other thesis, Murdoch University.

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The minority carrier lifetime distribution across silicon solar cells was investigated using variations of the open circuit voltage decay method. This was performed on monocrystalline, polycrystalline and amorphous silicon solar cells. Light from a white LED was focused using an aperture and a glass bi-convex lens to a spot size of 2mm on the surface of each cell investigated and moved in 1mm increments. At each point, a short pulse of light was emitted from the LED, with the open circuit voltage generated measured with time. This decay was then analysed using two calculation methods using a program written in LabVIEW. The generated minority carrier lifetime values at each point were exported in an array and plotted in Microsoft Excel, so that maps of the minority carrier lifetime were created.

The calculation method from Mahan et al. (Mahan et al. 1979), produced values of the minority carrier lifetime that were consistently lower than the results found using the method from Ranjan, Solanki and Lal (Ranjan, Solanki, and Lal 2008). The values of the minority carrier lifetime obtained in both instances were generally in the expected range, once abnormally high lifetimes found to be a result of external factors (such as increased background effects due to low LED intensities or measured open circuit voltages) were removed.

Due to the high levels of inaccuracy involved in analysis of the open circuit voltage decay curves, it was determined that this method could not produce reliable values of the minority carrier lifetime. However, through agreement of the two calculation methods used, the distribution of the minority carrier lifetime (such as regions of comparatively high and low lifetimes across a cell) could be determined with some accuracy in the case of the monocrystalline and polycrystalline silicon cells.

Item Type: Thesis (Other)
Murdoch Affiliation(s): School of Engineering and Energy
Supervisor(s): Parlevliet, David and Creagh, Chris
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