The World's #1 Renewable Energy Network for News, Information, and Companies.
Untitled Document

Funneling Solar Energy: A New Way to Harness the Sun

The quest to harness a broader spectrum of sunlight's energy to produce electricity has taken a radically new turn, with the proposal of a "solar energy funnel" that takes advantage of materials under elastic strain.

“We’re trying to use elastic strains to produce unprecedented properties,” says Ju Li, an MIT professor and corresponding author of a paper describing the new solar-funnel concept that was published this week in the journalNature Photonics.

In this case, the “funnel” is a metaphor: Electrons and their counterparts, holes — which are split off from atoms by the energy of photons — are driven to the center of the structure by electronic forces, not by gravity as in a household funnel. And yet, as it happens, the material actually does assume the shape of a funnel: It is a stretched sheet of vanishingly thin material, poked down at its center by a microscopic needle that indents the surface and produces a curved, funnel-like shape.

The pressure exerted by the needle imparts elastic strain, which increases toward the sheet’s center. The varying strain changes the atomic structure just enough to “tune” different sections to different wavelengths of light — including not just visible light, but also some of the invisible spectrum, which accounts for much of sunlight’s energy. 

Li, who holds joint appointments as the Battelle Energy Alliance Professor of Nuclear Science and Engineering and as a professor of materials science and engineering, sees the manipulation of strain in materials as opening a whole new field of research.

Strain — defined as the pushing or pulling of a material into a different shape — can be either elastic or inelastic. Xiaofeng Qian, a postdoc in MIT’s Department of Nuclear Science and Engineering who was a co-author of the paper, explains that elastic strain corresponds to stretched atomic bonds, while inelastic, or plastic, strain corresponds to broken or switched atomic bonds. A spring that is stretched and released is an example of elastic strain, whereas a piece of crumpled tinfoil is a case of plastic strain.

The new solar-funnel work uses precisely controlled elastic strain to govern electrons’ potential in the material. The MIT team used computer modeling to determine the effects of the strain on a thin layer of molybdenum disulfide (MoS2), a material that can form a film just a single molecule (about six angstroms) thick. 

It turns out that the elastic strain, and therefore the change that is induced in electrons’ potential energy, changes with their distance from the funnel’s center — much like the electron in a hydrogen atom, except this “artificial atom” is much larger in size and is two-dimensional. In the future, the researchers hope to carry out laboratory experiments to confirm the effect.

Unlike graphene, another prominent thin-film material, MoS2 is a natural semiconductor: It has a crucial characteristic, known as a bandgap, that allows it to be made into solar cells or integrated circuits. But unlike silicon, now used in most solar cells, placing the film under strain in the “solar energy funnel” configuration causes its bandgap to vary across the surface, so that different parts of it respond to different colors of light.

In an organic solar cell, the electron-hole pair, called an exciton, moves randomly through the material after being generated by photons, limiting the capacity for energy production. “It’s a diffusion process,” Qian says, “and it’s very inefficient.” 

But in the solar funnel, he adds, the electronic characteristics of the material “leads them to the collection site [at the film’s center], which should be more efficient for charge collection.”

The convergence of four trends, Li says, “has opened up this elastic strain engineering field recently”: the development of nanostructured materials, such as carbon nanotubes and MoS2, that are capable of retaining large amounts of elastic strain indefinitely; the development of the atomic force microscope and next-generation nanomechanical instruments, which impose force in a controlled manner; electron microscopy and synchrotron facilities, needed to directly measure the elastic strain field; and electronic-structure calculation methods for predicting the effects of elastic strain on a material’s physical and chemical properties.

“People knew for a long time that by applying high pressure, you can induce huge changes in material properties,” Li says. But more recent work has shown that controlling strain in different directions, such as shear and tension, can yield an enormous variety of properties. 

One of the first commercial applications of elastic-strain engineering was the achievement, by IBM and Intel, of a 50 percent improvement in velocity of electrons simply by imparting a 1 percent elastic strain on nanoscale silicon channels in transistors.

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

Untitled Document

Get All the Renewable Energy World News Delivered to Your Inbox - FREE!

Subscribe to Renewable Energy World Magazine and our award-winning e-Newsletter to stay up to date on current news and industry trends.

 Subscribe Now



A Case Study in Energy-Transition Momentum

Tim King South Australia is clearly at the forefront of the global energy transition as it establishes a fast-moving model oth...

Listen Up: Can I Get Solar if my Roof is Shaded?

The Energy Show on Renewable Energy World Rooftop solar panels only work when they are in direct sunlight. So if you have a partially shaded roof, the output o...

US Senate Democrats Unveil Energy Bill That Restores PTC and Extends ITC

Brian Eckhouse, Bloomberg Senate Democrats unveiled a bill that would provide more tax credits for renewable energy while killing some tax ince...

US, China Solar PV Players Team Up, Invest $100M in Chile, Uruguay and Japan

Andrew Burger Private equity infrastructure specialist Hudson Clean Energy Partners and Hong Kong-based independent power producer ...


Fronius Shifting the Limits in Solar-Plus: It’s not just about products, it’s about solutions.

Fronius USA, who just recently launched the all-new Fronius SnapINverter line this past...

IREC Announces Changes in Regulatory Team

The Interstate Renewable Energy Council (IREC), a not-for-profit organization which for...

IREC Awarded New Funding to Advance Digital Credentials

The Interstate Renewable Energy Council (IREC) proudly announces funding for an innovat...

$100 Discount on 5-day Advanced PV Project Experience Workhop

Upcoming 5-day Workshops: Nov. 7 - 11 Feb. 6 - 10


NY Gov. Cuomo Pledges to Create Carbon Market use Solar, Wind to reduce Climate Change

This week former Vice President Al Gore joined with New York Gov. Andrew Cuomo (D) to sign the Under 2 MOU, a directi...
clean energy

In Clean Energy, The Truth Matters

A group of about 20 protesters gathered outside the Sheraton in Burlington, Vt., early on Oct. 8 as attendees arrived...

Industry Focus: Cleantech: 1366 Technologies joins Solarcity in New York

1366 is set to build a factory just up the road (OK, it is a long road – NYS Thruway) from Solarcity.  The...



Volume 18, Issue 4


To register for our free
e-Newsletters, subscribe today:


Tweet the Editors! @jennrunyon



Successfully Integrating Solar: A Proactive Approach

•      What does the increasing solar penetrati...

Solar Power Asset Management and Performance

SEIA and SEPA collaborated with industry leaders to present the first ev...

Solar Power Northeast

  From the team that produced Solar Power Southeast and the sol...


Join us at the New Solar Power Northeast

From the team that produced Solar Power Southeast and the sold out P...

Saving Vs. Gaining

Whenever I do a national keynote speech or customized coaching session f...

SPI Brings Out The Best In Solar

Phew…...those cross-country flights sure take a lot out of a guy....


Renewable Energy: Subscribe Now

Solar Energy: Subscribe Now

Wind Energy: Subscribe Now

Geothermal Energy: Subscribe Now

Bioenergy: Subscribe Now