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In this study, we describe the fabrication of n-type solar cells using an industrial process. The open-circuit voltage limitation is discussed by investigating the influence of the screen-printed metallization at the front and rear sides. Efficiencies above 19.0% were obtained on 125PSQ Cz-Si wafers with a reference process. Narrow front metalized fingers were deposited by means of a stencil screen associated with a silver-plating step. Recombination below the contacts due to a metal area reduction resulted in a Voc improvement up to 5 mV. The process flow was then modified to develop an improved back-surface field (BSF). Measurements of implied Voc values on the cell precursors confirmed the interest of reducing the BSF doping level. Nevertheless, no gain in efficiency was achieved on full-metalized solar cells. A Voc limitation due to the metallization impact was also observed on several batches of solar cells. Specific light beam induced current measurements confirmed the need for a deep BSF profile to minimize recombination activity under the contact area. Finally, stability of the fabricated cell was investigated under light soaking. After over 100-h exposures, the cell efficiency was improved by 0.2% absolute, leading to a maximum efficiency of 19.3%.
Date of Publication: Oct. 2011