Light bulb moment

A light-emitting diode with the potential to be brighter and more efficient than current devices has been developed by Cranfield University researchers.

They say the technology will also be cheaper to manufacture and significantly more robust than current LEDs. The breakthrough has huge potential for improving the efficiency of many applications, from large advertising displays to mobile phones, PC monitors and televisions.

About 20 per cent of the world’s energy is used for lighting and light products, meaning an environmentally-friendly lighting solution could have a significant impact on energy consumption.

It has already been estimated that the widespread replacement of traditional bulbs with LED lighting could reduce energy use in this area by 10-50 per cent.

The new device, called a nano-LED and which has just been granted a patent, has the advantage that it does not need to be made within a clean room.

The solution is not water-sensitive: if the protective glass cover on a car dashboard or mobile phone display is cracked, the LED will not fail on exposure to airborne moisture.

The nanoparticles have the advantage of being temperature stable, so their colour will not change if, for instance, they are used in a vehicle that is left in the sun or is out in freezing conditions in winter.

According to its designers, the device is similar to a standard organic light-emitting diode (OLED) or polymeric light-emitting diode (PLED) device, but uses inorganic instead of organic materials.

OLEDs have been used to produce visual displays for portable electronic devices such as cellphones, digital cameras, and MP3 players. Larger displays have been demonstrated, but their life expectancy is still too short to be practical.

Dr Steve Dunn, lecturer in nanotechnology in Cranfield’s Microsystems and Nanotechnology Centre, said the technology will be complementary to PLEDs, though will have many advantages over the devices. ‘It is hard to work with polymers,’ said Dunn. ‘If water such as condensation gets in then this kills them.’

However, the nano-LEDs are created in water using a dipping technique, meaning that exposure to water will not destroy their luminescence.

While the materials used to manufacture organic LEDs are becoming more expensive, the nano-LEDs have been designed to use inorganic materials, thus reducing their cost.

Within the device, electrons and holes flow from one side to the other. When the two coincide, light shines out.

At present, the LEDs do not shine as brightly as would be necessary, although their efficiency is the same as a light bulb.

However, the team has established the cause for the lack of brightness and, as part of a 30-month programme, is now working to improve the flow of electrons and holes so that the amount of light produced is increased.

It is also looking for industrial partners to help with the technology’s development.

The nano-LED uses particles of a semi-conductor material that are about 3.5 nanometres in size.

Academics from Cranfield’s Microsystems and Nanotechnology Centre initially developed the technology for use in smart dashboards for cars but quickly realised its advantages for other applications.

Its manufacture allows the previously impossible ability to produce multi-coloured devices using only one process, as well as the ability to produce the device in an ambient environment without a need for clean rooms or dry atmospheres.

The process also allows manufacturers to produce pixels that range in size from a few tenths of a millimetre to many centimetres.

It may also be possible to use the device to produce pure white light, something that is proving particularly difficult with the technologies now on offer. Though nanoparticles are expensive, the device uses very few, again keeping manufacturing costs to a minimum and making the device commercially viable.