A team of researchers at MIT has developed a new type of textured solar surface that could bring down the cost of photovoltaic technology by reducing the thickness of silicon used by more than 90% while still maintaining high efficiency. To create the surface MIT modified a silicon sheet with a pattern of tiny inverted pyramids. These indentations, each less than a millionth of a meter across, are able to trap light rays just as effectively as solid silicon surfaces – which are 30 times thicker.

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The study is documented in the journal Nano Letters in a paper by MIT postdoc Anastassios Mavrokefalos, professor Gang Chen, and three other postdocs and graduate students, all from MIT’s Department of Mechanical Engineering. Speaking about the team’s breakthrough, Anastassios Mavrokefalos said: “We see our method as enhancing the performance of thin-film solar cells. It would enhance the efficiency, no matter what the thickness.”

Fellow team member Matthew Branham, a co-author of the paper, noted the cost efficiency benefits: “If you can dramatically cut the amount of silicon [in a solar cell] … you can potentially make a big difference in the cost of production. The problem is, when you make it very thin, it doesn’t absorb light as well.”

The team’s tiny surface indentations, also known  “inverted nanopyramids” greatly increase light absorption with only a 70% increase in surface area, limiting surface recombination. The innovation allows a sheet of crystalline silicon just 10 micrometers (millionths of a meter) thick to absorb light just as efficiently as a conventional silicon solar cell.

Not only would this reduce the cost of solar cells, but it would also reduce how much silicon is needed. The new technique also uses pre-existing equipment and materials that are already standard parts of silicon-chip processing, so new costs are incurred. “It’s very easy to fabricate,” Mavrokefalos says, yet “it attacks big problems.”

Currently the new silicon solar cell is only in the testing phase. The next step in the project 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. If the team is successful, then not only will the market soon see even cheaper solar cells, but their new thin design will enable them to be used in an even wider range of applications.


Images: MIT, Arenamontanus