Effect of Surface Cleaning on Laser Texturing of Multicrystalline Silicon Wafer

Abstract

A HF-free laser texturing process for multicrystalline silicon (mc-silicon) solar cell was developed and the effect of post-laser cleaning on the properties of the solar cell was investigated. Laser texturing of wafers was performed with a Nd-YAG picosecond laser with a wavelength of 1064 nm and anisotropic alkaline etching was performed using a TMAH/CH3COONa solution. The textured wafers showed a decrease in reflectance with increasing cleaning time while the cell efficiencies showed a maximum value of 15.2% after 5 min of cleaning at 70 degrees C. The TMAH/CH3COONa cleaning effectively removed the globules of laser-induced defects from the textured surfaces. In addition, the cleaning (etching) provided pseudo-pyramidal structures on the mc-silicon wafer surfaces. Accordingly, it was found that TMAH/CH3COONa cleaning may play a dual role of cleaning the laser-induced damage and anisotropic surface texturing. However, when the texturing process is accompanied with alkaline TMAH/CH3COONa cleaning, it was necessary to find the optimum etching time. The time should be long enough for removing the laser-induced damages and obtaining rough surfaces. At the same time, the time should not be so long to prevent the formation of high steps at the grain borders.