Grain growth behavior in a columnar-grain-structured silicon wafer for photovoltaic application

With direct growth technologies for obtaining ribbon-type silicon (Si) wafers from molten Si, the horizontal growth process is much faster than the vertical one in terms of the growth rate of the wafer. However, such a fast growth rate is likely to create grains of a relatively small size in the Si wafer, resulting in limited efficiency caused by grain boundary recombination. In this regard, controlling the grain growth behavior of the Si wafer with processing parameters such as the temperature of the substrate and its moving speed is very important in the horizontal growth process. The present investigation produced the experimental findings concerning the processing parameters for controlling the grain size. The size of the grains on the surface of the Si wafer increased to around 180 μm at a lower substrate temperature and a slower the moving speed of the substrate due to the increasing thickness of the Si wafer. However, the growth rate of the grains was observed to have little relation to the variations in the wafer thickness resulting from the processing parameters unless the nucleation behavior had been controlled.