Development Of Novel Surface Optical System For Multi-Crystalline Silicon Solar Cells

Light trapping structure for solar-grade multi-crystalline silicon wafers was prepared by low-cost alkaline etching. Antireflection coating with double-layer SiNx films were deposited to form a new-type optical system. By using scanning electron microscopy (SEM) and atomic force microscope (AFM), it was showed that the surface, with NaOH:NaNO2=1:1solution (wt%,75～80℃) etching for25seconds, was distributed with groove texture. Spectrophotometer was utilized to test reflectivity of silicon surfaces. The reflectivity was reduced to21.9%(X=650nm). After texturing treatment, double-layer SiNx films were deposited onto the surface, which reduced surface reflectivity significantly. The thickness of the film was in range of78to85nm, and refractive index was1.98to2.03, and the reflectivity of the mc-Si surface can be reduced to below3%. The efficiency of the mc-Si solar cell (156×156mm2) using the process above was15.6%, and the short circuit current was8.5A. Then a surface light trapping structure for solar-grade metallurgical silicon was developed. The results showed that the most effective process was that the surface etched by HF:HNO3:H2O=1:2.5:2(vol%,20±2℃) for30seconds. The surface of metallurgical silicon was distributed with uniform groove-like etched pits, and it had a very low reflectivity, which can be reduced to 21%(λ=650nm). Besides, novel texturing for quasi-single crystalline silicon solar cells was also developed. The method, using a HF:HNO3:H2O=1:2.5:2solution (20±2℃) for the first texturing treatment and a NaOH solution (10%,40℃) for the second texturing, results in a lowest reflectivity on silicon surface. After texturing treatment, the reflectivity of quasi-single crystalline silicon surface was reduced to20.9%(λ=650nm).