Texturization of diamond wire sawn multi-crystalline silicon wafers by micro-droplet etching

Diamond wire sawn multicrystalline silicon (DWS mc-Si) solar cell wafers have been known to be difficult to texturize by conventional acidic wet etching texturization process. A novel texturization method based on localized micro-droplet etching (MDE) has been developed, in which the micro-droplet is generated by controlled condensation of thermal vapor from a HF-HNO3-H2O bath. Uniformly distributed micron scale etch-pit type surface textures on DWS mc-Si wafers are made by the MDE process. Their light reflectivity is reduced to 18-21%, and their sawmarks are removed. Full size DWS mc-Si wafer samples were MDE textured, and send to a solar cell fabrication line along with the conventionally wet textured DWS mc-Si wafers as reference, without any adjustment of processing parameters for the MDE textured wafers. The average short circuit current of the MDE textured cells has been found to increase as compared to the reference cells, in a relative ratio approximately matching the final light reflection reduction ratio induced by the MDE textures. The average open circuit voltage and fill factor of the MDE textured cells are found to increase slightly, indicating that the MDE texture has not induced any significant increase in surface recombination of carriers, neither poorer contact of printed grid contact on cell surfaces. In average, 0.52% absolute increase of energy conversion efficiency is obtained.