Research On The Main Impurities And Defects In Mono-Like Silicon

The conversion efficiency of solar cells fabricated by traditional Czochralski silicon is higher because of less impurities and defects, but its production cost is high. While the production cost of cast multi-crystalline silicon is lower than that of Czochralski silicon, but there are large number of grain boundaries, dislocations and impurities. These factors have a significant influence on the properties of cast multi-crystalline silicon solar cells. Mono-like silicon combines the advantages of conventional Czochralski silicon and cast multi-crystalline silicon. The production cost of Mono-like silicon is lower than that of Czochralski silicon and conversion efficiency of solar cells is higher than that of cast multi-crystalline silicon. Mono-like silicon has a significant influence on the photovoltaic industry.In this paper, the surface morphologies, impurities and minority carrier lifetime of Mono-like silicon were analyzed by GEMINI detecting instrument, Fourier Transform Infrared Spectrometer and μ-PCD. The morphology and distribution characteristics of defects were studied by etching method.The experimental results showed that the surface morphologies of Mono-like silicon were related with their location. There was a large number of microcrystallines in the areas that contact with the crucible. The morphology of these areas was similar to that of cast multi-crystalline silicon. However, in the center area of silicon ingot, the single large crystal grain occupied99%, and the morphology was similar to that of Czochralski silicon.Many kinds of defect morphologies were observed in Mono-like silicon. There were not defects in most area, but the defect density in the edge was higher and increased from bottom to top gradually.The concentration of interstitial oxygen in Mono-like silicon ingot decreased gradually from the edge to the center and from the bottom to the top. The concentration of carbon increased gradually from the bottom to the top. The minority carrier lifetime was lower in silicon ingot top, bottom and the side that contacts with the crucible, while the center region of ingot was higher and distributed evenly. This characteristic was associated with the distribution of the impurities and defects.Excellent textured surfaces cannot be obtained by traditional texturing methods for Mono-like silicon, because its unique morphology and distribution of defects. The optimizing texturing process of Mono-like silicon was obtained. Pyramid structures on the surface of Mono-like silicon wafers were obtained and the surface reflection in the visible light region was reduced.