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Enhanced lateral current transport via the front N+ diffused layer of N-type high-efficiency back-junction back-contact silicon solar cells

: Granek, F.; Hermle, M.; Huljic, D.M.; Schultz-Wittmann, O.; Glunz, S.W.


Progress in Photovoltaics 17 (2009), No.1, pp.47-56
ISSN: 1062-7995
Journal Article
Fraunhofer ISE ()

N-type back-contact back-junction solar cells were processed with the use of industrially relevant structuring technologies such as screen-printing and laser processing. Application of the low-cost structuring technologies in the processing of the high-efficiency back-contact back-junction silicon solar cells results in a drastic increase of the pitch on the rear cell side. The pitch in the range of millimetres leads to a significant increase of the lateral base resistance. The application of a phosphorus doped front surface field (FSF) significantly reduces the lateral base resistance losses. This additional function of the phosphorus doped FSF in reducing the lateral resistance losses was investigated experimentally and by two-dimensional device simulations. Enhanced lateral majority carrier's current transport in the front n(+) diffused layer is a function of the pitch and the base resistivity. Experimental data show that the application of a FSF reduces the total series resistance of the measured cells with 3.5 mm pitch by 0.1 Omega cm(2) for the 1 Omega cm base resistivity and 1.3 Omega cm(2) for the 8 Omega cm base resistivity. Two-dimensional simulations of the electron current transport show that the electron current density in the front n+ diffused layer is around two orders of magnitude higher than in the base of the solar cell. The best efficiency of 21.3% was obtained for the solar cell with a 1 Omega cm specific base resistivity and a front surface field with sheet resistance of 148 Omega/sq.