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A Lawrence Berkeley National Lab research team has discovered a new way to process white OLEDs for solid-state lighting.

OLEDs based on organic and/or polymer semiconductor materials can cover large-area displays or panels using low-cost processing techniques. Single-color OLED displays are already available commercially. A mix of red-, green- and blue-emitting materials can be used to generate white light, but these bands of color often interact with one another, degrading device performance and reducing color quality.

Using polymer nanoparticles to house light-emitting inks, scientists at the Molecular Foundry have made a thin film OLED using iridium-based guest molecules to emit various colors of visible light. The polymer nanoparticle surrounding a guest light-emitter isolates guest molecules from one another. Each guest can then emit light without interactions with neighboring nanoparticles, resulting in white light.

“This simple and bright approach to achieving nanoscale site isolation of phosphors opens a new door for facile processing of white OLEDs for solid state lighting,” says Biwu Ma, a staff scientist with the Molecular Foundry’s Organic Nanostructures Facility. Ma and his colleagues plan to vary the ratio of each color nanoparticle in the OLED to enhance efficiency and brightness.

A paper reporting this appears in the journal Nano Letters.

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By changing the polarization direction of bismuth ferrite, these domain walls give rise to a photovoltaic effect. (Credit: Seidel, et. al.)

According to a Lawrence Berkeley National Laboratory press release, researchers have discovered a new path to convert sunlight to electricity. Researchers have found a new mechanism by which the photovoltaic effect can take place in semiconductor thin films. This new route to energy production overcomes the bandgap voltage limitation that continues to be detrimental to conventional solid-state solar cells.

Working with bismuth ferrite, researchers discovered that the application of an electric field makes it possible to manipulate the crystal structure and control the photovoltaic properties.

Working through LBNL’s Helios Solar Energy Research Center, Jan Seidel, a physicist who holds joint appointments with Berkeley Lab’s Materials Sciences Division and the UC Berkeley physics department, and his team discovered that by applying white light to bismuth ferrite they could generate photovoltages within submicroscopic areas between one and two nanometers across. These photovoltages were significantly higher than bismuth ferrite’s electronic bandgap.

At the domain walls, the polarization direction of the bismuth ferrite changes and the photovoltaic effect arises.

“While we have not yet demonstrated these possible new applications and devices, we believe that our research will stimulate concepts and thoughts that are based on this new direction for the photovoltaic effect,” Seidel says.

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A nitride thin film semiconductor material technology captures a wider spectrum of the sun's solar spectrum. (Credit: RoseStreet Labs Energy.)

A Phoenix company said it has created a hybrid solar cell that pairs a gallium-nitride thin film with typical silicon-based PV technology to produce a single unit it claims can achieve an efficiency of 25 percent to 30 percent.

RoseStreet Labs Energy announced the prototype cell Monday, and it expects to start commercial production late 2010, says Bob Forcier, CEO of RoseStreet. When those cells come off the first production line, they should be able to convert 25 percent to 30 percent of the sunlight that falls on them into electricity, he adds.

That kind of efficiency would be significantly greater than what the best silicon cells on the market can achieve today. Currently, the most efficient silicon cells for sale come from San Jose, Calif.-based SunPower, whose cells have 22.5 percent efficiency.

There are other types of cells that use alternative materials and perform much better than SunPower’s, but they also are much more expensive and are developed mostly for solar panels on satellites. The majority of the solar cells on the market today are made with silicon, and their efficiencies are typically in the mid-teens.

RoseStreet’s idea is that by adding a layer of gallium-nitride, PV panels can be tuned to make use of photons from a broader range of spectrum. “With gallium-nitride you can tune it for whatever [part of the spectrum] you want. It’s like a piano versus the ukulele – you get more notes with the piano,” Forcier says. “This technology allows silicon to be supercharged, like adding a big booster without a big cost penalty.”

Gallium-nitride is a common material for making LEDs, so sourcing it wouldn’t pose a challenge, he notes.

The company’s core technology came from Cornell University and the Lawrence Berkeley National Lab. RoseStreet’s chief technical officer is Wladek Walukiewicz, who also serves as a senior scientist at LBNL. Walukiewicz reached LBNL via the Warsaw Institute and at the Massachusetts Institute of Technology.

When the company announced its licensing agreement in 2005, it said the technology could lead to solar energy conversion efficiencies greater than 48 percent.

Although RoseStreet claims it will start production of the hybrid panels in late 2010, it could license its technology to other silicon makers that seek ways to significantly boost their products’ performance, Forcier says.

Interestingly, RoseStreet says its technology is not a one-trick pony. Two weeks ago, the company also announced that it had discovered a way to use a nitride thin film-based photoelectrochemical cell to produce hydrogen gas directly from sunlight.

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Arun Majumdar, who currently heads a Lawrence Berkeley National Lab project that aims to help India reduce its greenhouse gas emissions, has been nominated by President Obama to head the newly-created Advanced Research Projects Agency-Energy at the DOE.

The White House announced Majumdar’s nomination — which requires Senate confirmation — on Sept. 18. The IIT-Bombay graduate is not allowed to comment on the nomination until he is confirmed.

Majumdar — dubbed the nation’s new “green czar” by the press — is currently the associate laboratory director for energy and environment at Berkeley Labs in Berkeley, Calif. He also serves as a professor of mechanical engineering and materials science and engineering at UC-Berkeley.

ARPA-E was created in 2007, but only received its budget this February, under the Obama administration’s economic stimulus plan. The agency’s goals are to create technologies to reduce the country’s reliance on foreign energy and improve energy efficiency.

ARPA-E is also charged with reducing greenhouse gas emissions. At Berkeley Labs, Majumdar heads a collaboration between the U.S. and India that aims to reduce the latter’s greenhouse gas emissions while maintaining sustained economic growth.

The collaboration, the Berkeley-India Joint Leadership on Energy and the Environment, involves researchers from Lawrence Berkeley Labs and UC-Berkeley, and other U.S. and Indian universities and organizations.

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R&D Magazine hosts the R&D 100 Awards, which are presented annually to researchers who have developed the year’s 100 most outstanding advances in applied technologies. ACerS just learned that 49 out of the 100 awards were presented to U.S. national labs. The labs competed in an international pool that included universities, start-ups and large corporations.

Winners on the list that may be of particular interest include:

• Ultrasensitive Electrospray Ionization Mass Spectrometry Source and Interface, Pacific Northwest National Lab
• FemtoScope: a time microscope, Lawrence Livermore National Lab
• High-temperature Silicon Carbide Power Module, Sandia National Lab
• Argonne/Envia Composite Electrode Material Technology to Enable Plug-in Hybrids and All-Electric Vehicles, Argonne National Lab
• Nanocrystal Solar Cells, Lawrence Berkeley National Lab
• Clay-Liquid CO₂ Removal Sorbent, National Energy Technology Lab
• Fire-Resistive Phase Change Material, Oak Ridge National Lab
• NanoCoral Dendritic Platinum Nanostructures for Renewable Energy Applications, Sandia National Lab
• Hard X-Ray Nanoprobe, Argonne National Lab
• Hyperspectral Confocal Fluorescence Microscope System, Sandia National Lab
• Spectral Sentry—Protecting High-Intensity Lasers from Bandwidth-Related Damage, Lawrence Livermore National Lab
• Superhard and Slick Coating, Argonne National Lab
• Rhombohedral Single Crystal SiGe, NASA Langley Research Center

The DOE is particularly pleased with the awards. “The Department of Energy’s national laboratories are incubators of innovation, and I’m proud they are being recognized once again for their remarkable work,” says DOE Secretary Steven Chu. “The cutting-edge research and development being done in our national labs is vital to maintaining America’s competitive edge, increasing our nation’s energy security and protecting our environment. I want to thank this year’s winners for their work and congratulate them on this award.”

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