Nanotechnology for LEDs

Nanotechnology could lead to better, cheaper LEDs

LEDs are widely used in smartphones and portable electronics, and are also becoming more common in lighting. Researchers at Princeton University have developed a new method to increase the brightness, efficiency, and clarity of LEDs. Using a new nanoscale structure, researchers led by professor of electrical engineering Stephen Chow increased the brightness and efficiency of LEDs made from organic materials (carbon-based flexible sheets) by 57 percent. The researchers also report that their method should produce similar improvements in LEDs made from the inorganic (silicon-based) materials most commonly used today.

Image explanation -
(Picture A): Princeton researchers used their expertise in nanotechnology to develop a cost-effective new system. The illustration demonstrates how the structure of a traditional LED does not release most of the light generated inside the device. A new system called PlaCSH allows light to escape from the LED.
(Figure B): PlaCSH has a layer of light-emitting material about 100 nanometers thick, which is placed inside a cavity with one surface made of a thin metal film (shown on the left). The main part of the device is a metal mesh (center) with incredibly small dimensions, thickness - 15 nanometers. And each thread of the grid is about 20 nanometers wide and 200 nanometers between the centers of the holes. An image of the experimental LED is shown on the right. (Images courtesy of Stephen Chou et al.)

This method also improves the image clarity of LED displays by 400 percent over traditional approaches. In a paper published online Aug. 19 in the journal Advanced Functional Materials, the researchers describe how they achieved this by inventing a technique that manipulates light at a physical level of less than one wavelength.

"New nanotechnology could change the way light is manipulated," said Zhou, who has been working in the field for 30 years. "We can use this to create devices with unprecedented performance."

An LED is an electronic device that emits light when an electric current passes through it. LEDs have a number of advantages over incandescent or fluorescent lamps: they are much more efficient, compact and have a longer lifespan, which is important for portable displays.

In order to improve properties, developers in the field of modern LED technology are trying to solve some problems. First of all, this is a decrease in the amount of light reflected into the structure. While LEDs are known for their efficiency, only a very small amount of light generated inside an LED actually comes out.

“Lighting installed inside a swimming pool looks dim from the outside because the water reflects inward and captures the light. This is exactly what happens in the LED,” said Zhou, Professor of Engineering Joseph S. Elgin. "The solid structure of an LED absorbs much more light than pool water."

In fact, the LED, in its early designs, only emitted 2 to 4 percent of the light it generated. Absorbed light not only makes LEDs dim and energy efficient, but also makes them short-lived because the absorbed light heats up the LED, greatly reducing its lifespan.
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