New material discovered, absorbs wide range light with high efficiency

New material discovered, absorbs wide range of light with high efficiency

3:17 AM, 16th March 2012
New material discovered, absorbs wide range of light with high efficiency
Tapered ridges, made from alternating layers of metal and insulating material deposited on a surface, can produce a metamaterial that is tuned to a range of specific frequencies of light.

MASSACHUSETTS, US: Researchers at Massachusetts Institute of Technology (MIT) have found a way to use metamaterials to absorb a wide range of light with extremely high efficiency, which could lead to a new generation of solar cells or optical sensors. Metamaterials are a new class of artificial substances with unusual properties. Some have been designed to act as invisibility cloaks; others as superlenses, antenna systems or highly sensitive detectors.

According to Nicholas X Fang, Associate Professor, MIT the most thin materials used to fully capture light are limited to a very narrow range of wavelengths and angles of incidence. The new design uses a pattern of wedge-shaped ridges whose widths are precisely tuned to slow and capture light of a wide range of wavelengths and angles of incidence. These metamaterials can be extremely thin, saving weight and cost. Fang compares the tapered structures to the cochlea of the inner ear, which responds to different frequencies of sound at different points along its narrowing structure.

The actual structure of the material is etched from alternating layers of metal and an insulating material called a dielectric, whose response to polarized light can be varied by changing an electric field applied to the material.“What we have done is to design a multilayer sawtooth structure that can absorb a wide range of frequencies with an efficiency of more than 95 per cent. Previously, such efficiency could only be achieved with materials tuned to a very narrow band of wavelengths. High-efficiency absorption has been achieved before, but this design has an extremely wide window for colors of light,” said Kin Hung Fung, PhD, MIT.

The material can easily be fabricated using equipment that is already standard in conventional photovoltaic-cell manufacturing. Although the initial work was based on computer simulations, the team is now working on lab experiments to confirm their findings. Besides solar cells, the design could be used to make efficient infrared detectors for a selected range of wavelengths. “We can selectively enhance the material’s interaction with infrared light at the wavelengths we want,” said Fung.

Fang says that by its nature, the material would be both a very efficient emitter and absorber of photons, so in addition to potential uses in new kinds of solar cells or infrared detectors, the material could be used for infrared-light emitting applications, such as devices for generating electricity from heat. It could even be used to produce visible light with extremely low energy loss, creating a new kind of high-efficiency light bulb.

© Massachusetts Institute of Technology News

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