The findings, published in the journal Applied Physics Letters, piggyback on another University of Michigan advancement announced in the same journal late last year that could improve the chemistry of photovoltaic panels, including allowing manufacturers to eliminate toxic beryllium from the devices.
Together, the discoveries would make so-called “concentrator photovoltaics” that could be more than twice as efficient and 30 percent cheaper than traditional solar panels, the researchers said. Store-bought panels only convert around 15 percent of the sun’s energy, they said. Concentrator photovoltaics, on the other hand, have conversion rates of 50 percent.
“The implications are that you could have a boost in the efficiency and a reduction in the cost through these two innovations for wide scale deployment of concentrator photovoltaics on Earth,” said Rachel Goldman, a professor of materials science at Michigan and a co-author on the studies.
Currently, solar panels don’t capture infrared light that’s invisible to the naked eye.
But Goldman and her colleagues mixed a cocktail of arsenic, gallium arsenide, nitrogen, bismuth, and a material now used in solar panels, silicon, to create a layer of chemicals a few microns thick that they could spray onto photovoltaic cells to harness infrared energy. A micron is around .00004 inches.
"'Magic' is not a word we use often as materials scientists," Goldman said in a statement. "But that's what it felt like when we finally got it right."
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The other innovation involves simplifying the process of making semiconductors, or the chemical compounds that convert light into electricity in solar panels.
Currently, silicon is the routinely used semiconductor in solar panels. It doesn’t act alone, however. Solar panel makers add other chemicals to the silicon referred to as “designer impurities” or “dopants” to determine how it functions as a semiconductor.
Scientists have known for years that gallium arsenide — a combination of the metal gallium and arsenic — was potentially a more efficient semiconductor. But, for dopants, gallium arsenide semiconductors need silicon and beryllium. A component in nuclear weapons, beryllium is 10 times more expensive than silicon dopants and carcinogenic if mishandled.
Goldman, University of Michigan physics graduate student Richard Field, and others discovered how to eliminate the beryllium by reducing the levels of arsenic in the mix of dopants in gallium arsenide. As a result, the silicon dopants performed beryllium’s role in the semiconductor, behavior the researchers labelled “atomic ambidexterity.”
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Removing the beryllium would make gallium arsenide solar panels more practical for consumers. “Since you are using less material to basically do the same thing, it would cut the cost down,” said Field, who is now principal engineer at NanoFlex Power Corporation, an Ann Arbor-based company working on solar technology.
Engineers still need to take the researchers’ findings to develop new solar panels for the mass market, Goldman and Field said. But they hoped their work might inaugurate a new generation of better solar energy collectors on homes around the world.
“Once you have silicon and you optimize it, you optimize it,” said Field. “With gallium arsenide, you can add more things, you can tweak things. There is a lot more you can do.”
The National Science Foundation and US Department of Energy Office contributed funding to the study on infrared light. The National Science Foundation helped fund the research on silicon and beryllium dopants published last year.
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