(Press-News.org) NEW BRUNSWICK, N.J. – Physicists at Rutgers University have discovered new properties in a material that could result in efficient and inexpensive plastic solar cells for pollution-free electricity production.
The discovery, posted online and slated for publication in an upcoming issue of the journal Nature Materials, reveals that energy-carrying particles generated by packets of light can travel on the order of a thousand times farther in organic (carbon-based) semiconductors than scientists previously observed. This boosts scientists' hopes that solar cells based on this budding technology may one day overtake silicon solar cells in cost and performance, thereby increasing the practicality of solar-generated electricity as an alternate energy source to fossil fuels.
"Organic semiconductors are promising for solar cells and other uses, such as video displays, because they can be fabricated in large plastic sheets," said Vitaly Podzorov, assistant professor of Physics at Rutgers. "But their limited photo-voltaic conversion efficiency has held them back. We expect our discovery to stimulate further development and progress."
Podzorov and his colleagues observed that excitons – particles that form when semiconducting materials absorb photons, or light particles – can travel a thousand times farther in an extremely pure crystal organic semiconductor called rubrene. Until now, excitons were typically observed to travel less than 20 nanometers – billionths of a meter – in organic semiconductors.
"This is the first time we observed excitons migrating a few microns," said Podzorov, noting that they measured diffusion lengths from two to eight microns, or millionths of a meter. This is similar to exciton diffusion in inorganic solar cell materials such as silicon and gallium arsenide.
"Once the exciton diffusion distance becomes comparable to the light absorption length, you can collect most of the sunlight for energy conversion," he said.
Excitons are particle-like entities consisting of an electron and an electron hole (a positive charge attributed to the absence of an electron). They can generate a photo-voltage when they hit a semiconductor boundary or junction, and the electrons move to one side and the holes move to the other side of the junction. If excitons diffuse only tens of nanometers, only those closest to the junctions or boundaries generate photo-voltage. This accounts for the low electrical conversion efficiencies in today's organic solar cells.
"Now we lose 99 percent of the sunlight," Podzorov noted.
While the extremely pure rubrene crystals fabricated by the Rutgers physicists are suitable only for laboratory research at this time, the research shows that the exciton diffusion bottleneck is not an intrinsic limitation of organic semiconductors. Continuing development could result in more efficient and manufacturable materials.
The scientists discovered that excitons in their rubrene crystals behaved more like the excitons observed in inorganic crystals – a delocalized form known as Wannier-Mott, or WM, excitons. Scientists previously believed that only the more localized form of excitons, called Frenkel excitons, were present in organic semiconductors. WM excitons move more rapidly through crystal lattices, resulting in better opto-electronic properties.
Podzorov noted that the research also produced a new methodology of measuring excitons based on optical spectroscopy. Since excitons are not charged, they are hard to measure using conventional methods. The researchers developed a technique called polarization resolved photocurrent spectroscopy, which dissociates excitons at the crystal's surface and reveals a large photocurrent. The technique should be applicable to other materials, Podzorov claims.
INFORMATION:
Collaborating with Podzorov on the research were postdoctoral researcher Hikmat Najafov, graduate students Bumsu Lee and Qibin Zhou, and Leonard Feldman, director of the Rutgers Institute for Advanced Materials, Devices and Nanotechnology (IAMDN). Najafov and Podzorov are also affiliated with IAMDN.
Funding was provided by the National Science Foundation's Division of Materials Research and Japan's New Energy and Industrial Technology Development Organization (NEDO).
END
CORVALLIS, Ore. – The soils in large areas of the Southern Hemisphere, including major portions of Australia, Africa and South America, have been drying up in the past decade, a group of researchers conclude in the first major study to ever examine "evapotranspiration" on a global basis.
Most climate models have suggested that evapotranspiration, which is the movement of water from the land to the atmosphere, would increase with global warming. The new research, published online this week in the journal Nature, found that's exactly what was happening from 1982 to the ...
Researchers at the Georgia Institute of Technology and Emory University have developed a novel approach for delivering small bits of genetic material into the body to improve the treatment of inflammatory bowel diseases. Delivering short strands of RNA into cells has become a popular research area because of its potential therapeutic applications, but how to deliver them into targeted cells in a living organism has been an obstacle.
In the Oct. 10 advance online edition of the journal Nature Materials, researchers describe how they encapsulated short pieces of RNA into ...
Children who spend longer than two hours in front of a computer or television screen are more likely to suffer psychological difficulties, regardless of how physically active they are.
The PEACH project, a study of over a 1,000 children aged between ten and 11, measured the time children spent in front of a screen as well as their psychological well being. In addition, an activity monitor recorded both children's sedentary time and moderate physical activity. The results showed that more than two hours per day of both television viewing and recreational computer use ...
Racial disparities in the receipt of breast cancer care persist despite accounting for patients' insurance and social and economic status. That is the conclusion of a study published early online in Cancer, a peer-reviewed journal of the American Cancer Society. The findings suggest that greater efforts are needed to better understand disparities in breast cancer care and to ensure that all affected women receive equal and effective treatments.
Studies have demonstrated that black and Hispanic women are less likely to receive recommended breast cancer treatments than ...
Unless the IT industry adopts new energy-efficient technologies in the coming decade, it runs a serious risk of being unable to contribute to growing the global economy if limits are placed on carbon emissions. The findings come from an 18-month investigation by scholars at the Institute for Sustainable and Applied Infodynamics (ISAID) in Singapore and Rice University's Baker Institute for Public Policy in Houston.
"In the face of growing global concerns over greenhouse carbon emission, the key for the industry is finding new technologies that deliver more performance ...
For most American students, spending a semester or two studying in a foreign country means the opportunity to improve foreign language skills and become immersed in a different culture. For others, studying abroad is more like a prolonged spring break: it can be months with fewer academic responsibilities, plentiful bars and alcohol, and parents far away.
New results from University of Washington researchers point to why some students drink more alcohol while abroad and suggest ways to intervene.
"We hear stories in the media and elsewhere about students going abroad, ...
DALLAS – Oct. 11, 2010 – A clinical trial at UT Southwestern Medical Center aims to determine whether adding the hormone leptin to standard insulin therapy might help rein in the tumultuous blood-sugar levels of people with type 1 (insulin-dependent) diabetes.
This is the first type 1 diabetes treatment trial involving leptin, which is naturally produced by fat cells and involved in body-weight regulation. For this study, UT Southwestern researchers will be using metreleptin, a slightly modified form of the hormone that has been well-tolerated in other clinical trials.
"Leptin ...
Monarch butterflies appear to use medicinal plants to treat their offspring for disease, research by biologists at Emory University shows. Their findings were published online Oct. 6 in the journal Ecology Letters.
"We have shown that some species of milkweed, the larva's food plants, can reduce parasite infection in the monarchs," says Jaap de Roode, the evolutionary biologist who led the study. "And we have also found that infected female butterflies prefer to lay their eggs on plants that will make their offspring less sick, suggesting that monarchs have evolved the ...
The Colorado Cleantech Industry Association(CCIA) has released names of the finalists for its inaugural "Colorado Cleantech Awards Celebration" recognition event, honoring leadership in advancing cleantech. "Winners will be announced at our now officially sold-out event on Tuesday, October 19, 11 a.m. to 1 p.m., at the Denver Marriott City Center," Christine Shapard, CCIA Executive Director announces, "We're extremely pleased to share the twenty finalists who emerged from our statewide call for nominations."
CCIA - Leadership in Advancing Cleantech Awards - Finalists:
* ...
Chasing Arrows is a group of like-minded musicians that have integrated varied musical influences into a seamless dynamic whole. They have played the last several years up and down the East Coast for numerous enthusiastic audiences while sharing the stage with many notable acts including The Plain White T's, Carbon Leaf, Days Difference, Uh Huh Her and Vertical Horizon to name but a few. And to top it off, they were selected as first runner up for the MTVU Best Music on Campus Woodie Award in a competition that eliminated literally thousands of bands across the nation and ...
