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Effect of dislocations on open circuit voltage in crystalline silicon solar cells

: Kieliba, T.; Riepe, S.; Warta, W.


Journal of applied physics 100 (2006), Nr.9, Art. 093708, 6 S.
ISSN: 0021-8979
ISSN: 1089-7550
Fraunhofer ISE ()

The dislocation dependence of open circuit voltage is studied based on Donolato's model for the effect of dislocations on minority carrier effective diffusion length [J. Appl. Phys. 84, 2656 (1998)]. Experimental data measured on thin-film solar cells show a strong decrease of open circuit voltage V-oc with an increase in defect density. The analysis of the recombination currents indicates that V-oc is largely reduced by space charge region recombination. For a quantitative study on the relationship between dislocation density, effective diffusion length, and V-oc the data are fitted with an extended version of Donolato's model. Taking into account the base recombination current as well as the space charge region recombination current, the modeled curves fit very well to the experimental data. However, satisfactory fitting results require that the region of high recombination is set wider than the "effective depletion region width," which is calculated from the electrical field strength in a planar p-n junction. This effect can be explained with the assumption of a geometrical enlargement of the p-n junction due to defects like dislocations.