Wet Texturing of a Multi-Crystalline Si-Wafer Using the Phenol-Formaldehyde Resin Mask

Abstract

In the process of multi-crystalline silicon etched by the Metal Assisted Chemical Etching (MACE) method, due to its too small and uneven microstructures, heavy doping often occurs, which usually requires mixed acid (HNO3+HF) treatment, but this will ultimately affect the efficiency of crystalline silicon solar cells. In this article, phenol-formaldehyde (PF) resin, a main component of the positive photoresist, and water were dissolved in ethanol to form a PF resin-water-ethanol solution (PWEs) toward wet etching of multi-crystalline Si wafer, aim to prepared the texture structure with uniform distribution and reasonable size. A liquid film of PWEs was prepared on the Si wafer using dip-coating method. After the ethanol volatilizing, a mask of the resin was formed on the wafer through phase separation between the resin and water. A net like or a particle array mask was formed on the wafer through controlling the water/resin ratio, pulling speed and drying speed of the liquid film. With appropriate parameters above, a desirable particle array mask of PF resin was prepared. The size of particles and their spaces in this array were about $1{\mu }\text{m}$ and $2~{\mu }\text{m}$ respectively. With assistance of this particle array as a mask, a better textured surface of the Si wafer was prepared through MACE combined with etching of HNO3-HF mixed solution. The minimum reflectance of the wafer with the textured surface was as low as 14.2 %.