Industrialization of the laser diffusion process: Innovative concepts for increased production throughput

Laser doping or laser diffusion is a well-known process which serves to enhance the efficiency of crystalline solar cells. An increase of absolute cell efficiency of 0.3 - 0.5% has been demonstrated by using this method. In this process phosphorus is diffused from the surface into the bulk silicon at the locations were silicon is melted by laser irradiation. These locations are identical to the later contact finger locations. The sheet resistance of the laser treated areas are strongly reduced, compared to the non-treated area, e.g. from 120-150 Ohm/sq to typically 20 - 30Ohm/sq. Although the process itself is well known by now, the debate of how to apply the laser beam in the most efficient and time saving way is still going on. In this work we present a unique beam splitter technology which opens the path to simultaneous processing of several 10 to more than 100 contact fingers at the same time. In combination with a green laser with long pulses, which reduces surface and bulk damage to a minimum, a technology for very fast laser doping of high quality solar cells is available.