MIT researchers look to funnel sunlight for power

 A visualization of the broad-spectrum solar energy funnel. Image: Yan LiangIn an attempt capture more of the solar spectrum, MIT researchers are looking a new class of so-called ultrastrength materials to create a kind of solar energy funnel to produce electricity using elastic strain. The researchers published their work in Nature Photonics this week.

Usually a photovoltaic material creates electricity when a particular bandgap of sunlight hits its surface, the funnel being developed at MIT could absorb more of sunlight bandgap because different parts of the device would react to different parts of the funnel.

Still, the funnel isn’t a conventional funnel by any means. It’s more than microscopic. It’s molecule thick sheet poked into a funnel-shape by a microscopic needle, according to MIT. “We’re] using large elastic strains to change the physical and chemical properties of materials,” Ju Li, MIT’s Battelle Energy Alliance professor of Nuclear Science and Engineering and a professor of materials science and engineering who co-authored the article with Xiaofeng Qian, a postdoc in MIT’s Department of Nuclear Science and Engineering program. 

“One example is we designed a stretched molybdenum disulfide membrane which is an atomic sheet of semiconductor. And by applying the strain we can change the bandgap from about 2 electron volts to about 1.1. electron volts,” he said. By changing the bandgap of the material Li thinks the device can absorb more sun. “With that we hope to collect the raw spectrum of solar energy and also have a new design for photovoltaics,” he said.

The result is a potentially more efficient converter of electricity than other forms PV generation. Whereas in a normal PV cell, electrons move somewhat inefficiently through the semiconductor, the funnel leads electrons to the device’s center where they could  potentially more efficiently.

Manipulating strain could be a whole new field of research, according to Lu, and could have impacts far beyond photovoltaic materials. The elastic strain engineering field was recently made possible by some key factors, according to Li. They include nanostructured materials, like Graphene and MoS2, that can retain large amounts of elastic strain indefinitely as well as the development of the atomic force microscope and next-generation nanomechanical instruments, electron microscopy and synchrotron facilities and electronic-structure calculation methods, Li told MIT’s news service.

The work was conducted with the Ji Feng of Peking University and Cheng-Wei Huang. It was supported by the U.S. National Science Foundation, the U.S. Air Force Office of Scientific Research, and China’s National Natural Science Foundation.

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