Lasers & Sources

Princeton nanotechnology increases LED brightness and efficiency by 57%

Sept. 26, 2014

Using their expertise in nanotechnology, Princeton researchers developed an economical new system that markedly increases the brightness, efficiency, and clarity of LEDs that are widely used in smartphones and other electronics. The illustration demonstrates how a conventional LED structure traps most of the light generated inside the device; the new system, called PlaCSH, guides the light out of the LED.

Using a new nanoscale structure, Princeton researchers led by electrical engineering professor Stephen Chou increased the brightness and efficiency of light-emitting diodes (LEDs) made of organic materials (flexible carbon-based sheets) by 57%. The researchers also report their method should yield similar improvements in LEDs made in inorganic (silicon-based) materials used most commonly today.

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The solution presented by Chou's team is the invention of a nanotechnology structure called PlaCSH (plasmonic cavity with subwavelength hole-array). The researchers reported that PlaCSH increased the efficiency of light extraction to 60%, which is 57% higher than conventional high-end organic LEDs. At the same time, the researchers reported that PlaCSH increased the contrast (clarity in ambient light) by 400%. The higher brightness also relieves the heating problem caused by the light trapped in standard LEDs.

Chou first used the PlaCSH structure on solar cells, which convert light to electricity. In a 2012 paper, he described how the application of PlaCSH resulted in the absorption of as much as 96% of the light striking solar cells' surface and increased the cells' efficiency by 175%. Chou realized that a device that was good at absorbing light from the outside could also be good at radiating light generated inside the device--offering an efficient solution for both light extraction and the reduction of light reflection.

The physics behind PlaCSH are complex, but the structure is relatively simple. PlaCSH has a layer of light-emitting material about 100 nm thick that is placed inside a cavity with one surface made of a thin metal film. The other cavity surface is made of a metal mesh with incredibly small dimensions: it is 15 nm thick; and each wire is about 20 nm in width and 200 nm apart from center to center.

Because PlaCSH works by guiding the light out of the LED, it is able to focus more of the light toward the viewer. The system also replaces the conventional brittle transparent electrode, making it far more flexible than most current displays. Another benefit for manufacturers is cost. The PlaCSH organic LEDs were made by nanoimprint, a technology Chou invented in 1995, which creates nanostructures in a fashion similar to a printing press producing newspapers.

The method also improves the picture clarity of LED displays by 400% compared with conventional approaches. The article published online August 19 in the journal Advanced Functional Materials describes the work.

SOURCE: Princeton University; http://www.princeton.edu/main/news/archive/S41/14/79S63/index.xml?section=topstories

About the Author

Gail Overton | Senior Editor (2004-2020)

Gail has more than 30 years of engineering, marketing, product management, and editorial experience in the photonics and optical communications industry. Before joining the staff at Laser Focus World in 2004, she held many product management and product marketing roles in the fiber-optics industry, most notably at Hughes (El Segundo, CA), GTE Labs (Waltham, MA), Corning (Corning, NY), Photon Kinetics (Beaverton, OR), and Newport Corporation (Irvine, CA). During her marketing career, Gail published articles in WDM Solutions and Sensors magazine and traveled internationally to conduct product and sales training. Gail received her BS degree in physics, with an emphasis in optics, from San Diego State University in San Diego, CA in May 1986.