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Researchers at MIT have devised a way to reduce the amount of expensive, highly purified silicon needed to make solar cells. They increased light absorption of the cells by etching tiny surface indentations described as “inverted nanopyramids” that may reduce the thickness of the silicon used in solar cells by more than 90 per cent while still maintaining high efficiency.
These tiny indentations, each less than a micrometre, can trap rays of light as effectively as conventional solid silicon surfaces that are 30 times thicker, the findings by MIT postdoc Anastassios Mavrokefalos, professor Gang Chen, and three other postdocs and graduate students of MIT’s Department of Mechanical Engineering show.
Besides cost reduction, the method also cut the weight of the cells, which in turn would reduce the material needed for frames and supports. The potential cost savings are not only in the cell material, but also in the installation costs. The technique uses equipment and materials that are already standard parts of silicon-chip processing, so no new manufacturing machinery or chemicals would be required.
So far, the first step towards making the new type of solar cells has been carried out, producing the patterned surface on a silicon wafer and demonstrating its improvement in trapping light. The next step will be to add components to produce an actual photovoltaic cell and then show that its efficiency is comparable to that of conventional solar cells. It is expected to produce energy-conversion efficiencies of about 20 per cent, compared to 24 per cent for the best current commercial silicon solar cells.
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