New Alloy Could Make For Highly Efficient Solar Cells

The main growth chamber where the new alloy was constructed. Joseph Xu

Researchers at the University of Michigan have unveiled a newly developed alloy that they believe could push the efficiency of solar cells easily beyond 50 percent.

The new semiconductor is made of a mixture of arsenic, gallium, bismuth, and nitrogen and is 25-percent less expensive than previously tested alloys. The team believe this is the world’s most cost-effective material that's capable of absorbing near-infrared light. The discovery is reported in Applied Physics Letters.

The new material could be used in the newest generation of solar cells, known as concentrator photovoltaics. These cells are expected to double the efficiency of solar panels, which is currently around the 25 percent mark.

"Flat-panel silicon is basically maxed out in terms of efficiency," Professor Rachel Goldman, whose lab developed the alloy, said in a statement. "The cost of silicon isn't going down and efficiency isn't going up. Concentrator photovoltaics could power the next generation."

Current concentrators are made of three materials that absorb different wavelengths of lights. Each material is “sprayed” on top of each other so that they are in thin layers just a few microns thick. Using multiple materials allows each layer to focus on certain types of light. If one layer doesn’t stop a particular photon, another will.

One of the big hurdles for this tech is the lack of absorption of near-infrared light. Researchers worldwide have been struggling to catch these sun-rays and have been looking for a fourth layer. This layer needs to not only be sensitive to infrared light, it also needs to be stable, durable, and with an atomic structure that can match the other three layers. And, obviously, it needs to be cost effective.

The new material does all that. The researchers used advanced imaging techniques using X-rays and ions to study the alloy molecules directly and discovered that a slightly different type of arsenic paired with bismuth more effectively. In addition, they found that a different nitrogen-bismuth mix reduced the number of manufacturing steps, and they also discovered the right temperature to have the elements mixed securely.

"Essentially, this enables us to make these semiconductors with fewer atomic spray cans, and each can is significantly less expensive," Goldman said. "In the manufacturing world, that kind of simplification is very significant.

"'Magic' is not a word we use often as materials scientists," Goldman added. "But that's what it felt like when we finally got it right."

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