Sharp Corporation has just announced that it has achieved the world’s highest solar cell conversion efficiency using a compound layered design based on the technology used in the solar cells that power space satellites. Mindful of the link between sustainable energy and the future market for consumer electronics, Sharp has been aggressively pursuing solar efficiency improvements that lend themselves to commercial application.
Instead of silicon, compound solar cells use two or more photo-absorption layers composed of different elements. The trick is to find materials that generate the most current with the least waste. Sharp’s innovation is a proprietary technology that enables it to produce a high-efficiency crystalline compound, InGaAs (indium-gallium-arsenide), which boosted the efficiency of Sharp’s previous cells from 31.5% to 35.8%.
Solar Cell Efficiency Records on the Rise
So far, Sharp’s new triple-junction compound solar cell beats out the achievements of conventional silicon-based technology, but even silicon cells are showing rapid improvements. Last year researchers at the University of South Wales in Australia announced the first silicon cell to reach 25% conversion efficiency, and this summer that SunTech announced a solar conversion efficiency of 15.6% for its multi-crystalline silicon solar module. MIT scientists are working on an organic dye that could boost solar cell efficiency by 50%, and the U.S. Department of Energy has awarded a grant to develop an anti-reflective coating that boosts solar efficiency for thin film solar cells.
Compound Solar Cells
Compound solar cells typically include a bottom layer of germanium (Ge), which is relatively easy to manufacture. On the down side, Ge wastes most of the current that it generates. Sharp’s InGaAs has a much higher efficiency but it is difficult to produce in the desired high crystalline form. Sharp was able to solve the problem through its proprietary process for forming the layers in the cell, a breakthrough that it credits to working with NEDO, Japan’s public entity for promoting research and development.
A Note on Solar Efficiency
The number of solar products in and out of development is skyrocketing, and there are various means and standards of judging conversion efficiency. Sharp bases its claim of 35.8% efficiency on a cell surface of approximately one square centimeter, as confirmed by Japan’s National Institute of Advanced Industrial Science and Technology. Working with a team of U.S. researchers, the University of South Wales has achieved 43% solar conversion efficiency using a combination of five cells, one silicon and the other four composed of gallium, indium, phosphorus and arsenic, as verified by the National Renewable Energy Laboratory in the U.S. The design is far from commercial viability, but it provides a glimpse of still more improvements in solar efficiency to come.
Image: X-ray image of the sun by NASA Godard Laboratory via wikimediacommons.
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