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International Journal of Photoenergy
Volume 2013 (2013), Article ID 368403, 8 pages
http://dx.doi.org/10.1155/2013/368403
Research Article

Optimization of Rear Local Contacts on High Efficiency PERC Solar Cells Structures

Applied Materials, 3535 Garrett Drive, Santa Clara, CA 95054, USA

Received 1 February 2013; Revised 11 March 2013; Accepted 14 March 2013

Academic Editor: Sudhakar Shet

Copyright © 2013 Kapila Wijekoon et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

A local contact formation process and integration scheme have been developed for the fabrication of rear passivated point contact solar cells. Conversion efficiency of 19.6% was achieved using  mm, pseudo square, p-type single crystalline silicon wafers. This is a significant improvement when compared to unpassivated, full area aluminum back surface field solar cells, which exhibit only 18.9% conversion efficiency on the same wafer type. The effect of rear contact formation on cell efficiency was studied as a function of contact area and contact pitch, hence the metallization fraction. Contact shape and the thickness of Al-BSF layer were found to be heavily dependent on the laser ablation pattern and contact area. Simulated cell parameters as a function of metallization showed that there is a tradeoff between open circuit voltage and fill factor gains as the metallization fraction varies. The rear surface was passivated with an Al2O3 layer and a capping layer. The rear surface contact pattern was created by laser ablation and the contact geometry was optimized to obtain voids free contact filling, resulting in a uniform back surface field. The efficiency gain in rear passivated cells over the reference cells is mainly due to improved short circuit current and open circuit voltage.