Nanolayer boosts LED output to 99 percent
Researchers at Imperial College London and the Indian Institute of Technology (IIT) Guwahati have used a 2D nanolayer to boost the output of LED devices.
The team modelled the impact of placing a two-dimensional (single layer) of nanoparticles between the LED chip, which produces the light, and the transparent casing that protects the chip. Although the casing is necessary, it can cause unwanted reflections of the light emitted from the LED chip, meaning not all the light escapes.
They found that adding a layer of finely tuned silver nanoparticles could reduce these reflections, allowing up to 20 percent more light to be emitted. The reflections also increase the heat inside the device, degrading the LED chip faster, so reducing the reflections could also reduce the heat and increase the lifetime of LED chips.
This ‘meta-grid’ of sub-wavelength-sized plasmonic nanoparticles (NPs) boosts the transmission through destructive interference between light reflected from the chip/encapsulant interface. The theory says this can increase the transmission across the interface at the peak emission wavelength to 99 percent, up from a typical value of 84 percent.
“While improvements to the casing have been suggested previously, most make the LED bulkier or more difficult to manufacture, diminishing the economic effect of the improvement,” said Dr Debabrata Sikdar from IIT Guwahati, formerly a European Commission Marie Curie-Sklodowska Fellow at Imperial.
“We think that our innovation, based on fundamental theory and the detailed, balanced optimization analysis we performed, could be introduced into existing manufacturing processes with little disruption or added bulk,” she said.
“The simplicity of the proposed scheme and the clear physics underpinning it should make it robust and, hopefully, easily adaptable to the existing LED manufacturing process,” said Professor Sir John Pendry, from the Department of Physics at Imperial.
“It is obvious that with larger light extraction efficiency, LEDs will provide greater energy savings as well as longer lifetime of the devices. This will definitely have a global impact on the versatile LED-based applications and their multi-billion-dollar market worldwide,” he added.
Next: Manufacturing the layer
The next stage for the research will be manufacturing a prototype LED device with a nanoparticle layer, testing the best configurations predicted by the theory – including the size, shape, material and spacing of the nanoparticles, and how far the layer should be from the LED chip.
The principles can work along with other existing schemes implemented for enhancing light extraction efficiency of LEDs. The same scheme could also apply to other optical devices where the transmission of light across interfaces is crucial, such as in solar cells.
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