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Making light of it



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A cadre of researchers at Pacific Northwest National Laboratory is laying the groundwork for success with the most promising new lighting technology to emerge since liquid crystal displays (LCD). The light source is organic diodes--simple semiconductors--and the technology is revolutionizing electronic displays for digital cameras, cell phones, car stereos, and even some prototype computer monitors. These organic light-emitting diodes (OLEDs) are brighter and sharper than the ubiquitous LCDs, and they use less energy as well. In the not-too-distant future, OLEDs may illuminate thin, flexible large-screen televisions and computer monitors that can be rolled up for storage.

While OLEDs are transforming display lighting, the PNNL researchers are taking the technology to the next level solid-state lighting. They anticipate being able to construct flexible, transparent, solid-state lighting panels that can be wrapped around a column or applied flat on a wall, window or ceiling like wallpaper. Their challenge is to take the best features of OLEDs--exceptional brightness, quick response time, inexpensive materials and low energy consumption--and scale them up to room-size, general white lighting. A major obstacle to developing OLEDs is a lack of high-performance materials. PNNL scientists are hard at work designing low-voltage, stable organic materials that produce light as bright as a fluorescent panel and more energy-efficient than an incandescent bulb.

The process of creating OLEDs begins on the molecular level, as the scientists design and create organic molecules specifically for maximum light output. "We are structuring matter at the nanoscale," said Paul Burrows, PNNL's Nanoscience and Technology Initiative manager, "where materials behave differently than they do in bulk. We can design and construct molecules to perform specific functions. We are creating molecules whose chemical properties allow them to emit light when a low-voltage electrical current is applied, a process called electroluminescence."

The luminescent molecules are fabricated into a coating or thin film that is a mere 100 to 150 nanometers thick (less than one percent of the diameter of a human hair). This film is then layered between two electrodes, at least one of which must be transparent to let the light shine through. When an electric current is passed between the electrodes and through the organic layer, light is produced. The desired thickness of OLED film is deposited onto a substrate like glass or lightweight, flexible plastic, such as polyethylene terephthalate (PET), the plastic used for pop and water bottles.

Burrows is confident of success in their endeavor. "We have the equipment, the staff and the knowledge to achieve our objectives," he said. "Our team has expertise in molecular design, materials fabrication, thin film deposition, and flexible coatings and application." The equipment consists of the surface/nanoscale analytical facility at the Environmental Molecular Sciences Laboratory (EMSL), where scientists design and structure the organic molecules, and a new lab where the OLED film is deposited on PET at up to 300 feet per minute.

Produced efficiently and inexpensively enough to compete with fluorescent and incandescent light bulbs in the marketplace, OLEDs could by 2020 reduce the amount of electricity used for lighting in the U.S. by 50 percent.

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