New Nanomaterial Increases Yield of Solar Cells


 

New nanomaterial increases yield of solar cells  6 hours ago

Linked quantum dots – In the new nanomaterial two or more electrons jump across the band gap as a consequence of just a single light particle (arrow with waves) being absorbed. Using special molecules the researchers have strongly linked the …more

Researchers from the FOM Foundation, Delft University of Technology, Toyota Motor Europe and the University of California have developed a nanostructure with which they can make solar cells highly efficient. The researchers published their findings on 23 August 2Researchers from the FOM Foundation, Delft University of Technology, Toyota Motor Europe and the University of California have developed a nanostructure with which they can make solar cells highly efficient. The researchers published their findings on 23 August 2013 in the online edition of Nature Communications.

Smart nanostructures can increase the yield of . An international team of researchers including physicists from the FOM Foundation, Delft University of Technology and Toyota, have now optimised the so that the solar cell provides more electricity and loses less energy in the form of heat.

Solar cells

A conventional solar cell contains a layer of silicon. When sunlight falls on this layer, in the silicon absorb the energy of the (photons). Using this energy the electrons jump across a ‘‘, as a result of which they can freely move and electricity flows.

The yield of a solar cell is optimised if the is equal to the band gap of silicon. Sunlight, however, contains many photons with energies greater than the band gap. The excess energy is lost as heat, which limits the yield of a conventional solar cell.

Nanospheres

Several years ago the researchers from Delft University of Technology, as well as other physicists, demonstrated that the excess energy could still be put to good use. In small spheres of a the enables extra electrons to jump across the band gap. These nanospheres, the so-called , have a diameter of just one ten thousandth of a .

If a light particle enables an electron in a quantum dot to cross the band gap, the electron moves around in the dot. That ensures that the electron collides with other electrons that subsequently jump across the band gap as well. As a result of this process a single photon can mobilize several electrons thereby multiplying the amount of current produced.

Contact between quantum dots

However, up until now the problem was that the electrons remained trapped in their quantum dots and so could not contribute to the current in the solar cell. That was due to the large molecules that stabilize the surface of quantum dots. These large molecules hinder the electrons jumping from one quantum dot to the next and so no current flows.

In the new design, the researchers replaced the large molecules with small molecules and filled the empty space between the quantum dots with aluminium oxide. This led to far more contact between the quantum dots allowing the electrons to move freely.

Yield

Using laser spectroscopy the physicists saw that a single photon indeed caused the release of several electrons in the material containing linked quantum dots. All of the electrons that jumped across the band gap moved freely around in the material. As a result of this the theoretical yield of solar cells containing such materials rises to 45%, which is more than 10% higher than a conventional solar cell.

This more efficient type of solar cell is easy to produce: the structure of linked nanospheres can be applied to the solar cell as a type of layered paint. Consequently the new solar cells will not only be more efficient but also cheaper than conventional cells.

The Dutch researchers now want to work with international partners to produce complete solar cells using this design.

Read more at: http://phys.org/news/2013-08-nanomaterial-yield-solar-cells.html#jCpn mobilise several electrons thereby multiplying the amount of current produced.

 

Read more at: http://phys.org/news/2013-08-nanomaterial-yield-solar-cells.html#jCp

Scientists demonstrate high-efficiency quantum dot solar cells


 

Research shows newly developed solar powered cells may soon outperform conventional photovoltaic technology. Scientists from the National Renewable Energy Laboratory (NREL) have demonstrated the first solar cell with external quantum efficiency (EQE) exceeding 100 percent for photons with energies in the solar range. (The EQE is the percentage of photons that get converted into electrons within the device.) The researchers will present their findings at the AVS 59th International Symposium and Exhibition, held Oct. 28 — Nov. 2, in Tampa, Fla.

While traditional semiconductors only produce one electron from each photon, nanometer-sized crystalline materials such as quantum dots avoid this restriction and are being developed as promising photovoltaic materials. An increase in the efficiency comes from quantum dots harvesting energy that would otherwise be lost as heat in conventional semiconductors. The amount of heat loss is reduced and the resulting energy is funneled into creating more electrical current.

By harnessing the power of a process called multiple exciton generation (MEG), the researchers were able to show that on average, each blue photon absorbed can generate up to 30 percent more current than conventional technology allows. MEG works by efficiently splitting and using a greater portion of the energy in the higher-energy photons. The researchers demonstrated an EQE value of 114 percent for 3.5 eV photons, proving the feasibility of this concept in a working device.

Joseph Luther, a senior scientist at NREL, believes MEG technology is the right direction. “Since current solar cell technology is still too expensive to completely compete with non-renewable energy sources, this technology employing MEG demonstrates that the way in which scientists and engineers think about converting solar photons to electricity is constantly changing,” Luther said. “There may be a chance to dramatically increase the efficiency of a module, which could result in solar panels that are much cheaper than non-renewable energy sources.”

 

Researchers to Study Quantum Metamaterials


Published on October 4, 2012 at 4:34 AM

Through a new Multidisciplinary University Research Initiative (MURI) awarded by the Air Force Office of Scientific Research, researchers from Brown University will lead an effort to study new optical materials and their interactions with light quantum scale. The initiative, titled Quantum Metaphotonics and Quantum Metamaterials, will receive $4.5 million over three years, with a possible two-year extension.

“The field of metamaterials has already expanded the range of optical materials and phenomenon available at larger, classical scales,” said Rashid Zia, Manning assistant professor of engineering and the lead investigator of the initiative. “What we’re doing now is asking what happens when we bring these metamaterials down to the scale of quantum emitters.”

Harnessing the power of light at the quantum scale could clear the way for super-fast optical microprocessors, high-capacity optical memory, securely encrypted communication, and untold other technologies. But before any of these potential applications sees the light of day, there are substantial obstacles to overcome. Not the least of which is the fact that the wavelength of light is larger than quantum-scale objects, limiting the range of possible light-matter interactions.

“The optical wavelength is approximately 100 times larger than a quantum emitter,” Zia said. “So we need to find ways of overcoming this size mismatch to increase interactions at the quantum scale, for example by shrinking the optical wavelength in highly confined metamaterial cavities. And hopefully we can learn something fundamental about the nature of light that opens up news ways of manipulating it to increase these interactions.”

The Quantum Metaphotonics and Metamaterials MURI team includes:

Harry Atwater, California Institute of Technology

Seth Bank, University of Texas at Austin

Mark Brongersma, Stanford University

Nader Engheta, University of Pennsylvania

Shanhui Fan, Stanford University

Nicholas Fang, Massachusetts Institute of Technology

Arto Nurmikko, Brown University

Jelena Vuckovic, Stanford University

Xiang Zhang, University of California, Berkeley

Rashid Zia, Brown University

“It’s really an exciting project,” Zia said. “Over the next five years, this program will bring together 10 groups and 40-plus researchers with complementary expertise to help answer questions that we couldn’t have imagined a short time ago. We are very optimistic about where this will lead.”

Source: http://www.brown.edu/about