Advanced alignment technique for precise printing over selective emitter in c-Si solar cells

Significant improvements in c-Si solar cells performance can be achieved acting on the emitter or on the contact formation side. At the moment, an efficiency gain around 0.50.6%abs [1] has been demonstrated for selective emitter (SE) cells, mainly caused by the improvement of the blue response of the shallow emitter. Nevertheless, in case of sub-optimal alignment of the printed metal with the deep emitter, the shallow junction depth leads to a significantly narrower firing process window, consequently causing high contact resistance and poor shunting behavior. Moreover, after Anti Reflective Coating (ARC) the contrast between differently doped areas is poor and often prevents the screen printer vision system from correctly recognizing the pattern for metal printing alignment. Thus, we developed a new equipment, high precision selective emitter, for precise alignment over SE able to guarantee recognition of every SE pattern and consequent printing repeatability within +/-30?mu m without rejections or misalignments. In this work, results from experimental investigations and mass production are reported and discussed, including also comparison with standard alignment methods and further feasible applications. New equipment for precise alignment over SE able to guarantee recognition of every SE pattern and consequent printing repeatability within +/-30 mu m without rejections or misalignments has been developed (examples of SE patterns are reported in the following pictures). Test performed at production sites confirm that an efficiency gain of 0.1% and a significant reduction of rejection can result from the increased robustness of the presented method. Finally, also a correlation between sheet resistance of heavily doped area and image contrast has been demonstrated. Copyright (c) 2011 John Wiley & Sons, Ltd.