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Posted: May 15, 2009
The future is bright for novel light sources
(Nanowerk News) EU-funded researchers have created organic light-emitting diodes (OLEDs, novel, bright light sources) that are as efficient as conventional fluorescent tubes. Writing in the journal Nature, the scientists describe the future of OLEDs as 'bright, not only because of their high illumination quality, but also because their outstanding efficiencies will help to reduce our carbon footprint'.
EU support for the work came from the OLLA ('Organic LEDs for ICT [Information and Communication Technology] and lighting applications') project, which is financed through the 'Information Society Technologies' Thematic area of the Sixth Framework Programme (FP6).
OLEDs, which are semiconductors made of layers of organic material just nanometres thick, are widely touted as 'the light source of the future'. In addition to their potential as highly energy-efficient light sources, OLEDs could also be used for display purposes, allowing users to combine colours and shapes to personalise their surroundings with light, for example. Thin and flexible, OLEDs could also be used to make screens that can be rolled up.
However, until now, the most energy-efficient OLEDs reported in the scientific literature had efficiencies of just 44 lumens per watt (lm/W), far below the range of 60 lm/W to 70 lm/W, the efficiency levels of conventional fluorescent tubes.
In this latest study, scientists from the Technical University of Dresden in Germany explain how they surpassed the 60 lm/W to 70 lm/W mark, reaching efficiency levels of 90 lm/W at a brightness of 1,000 candelas per square metre.
'In our approach, we combine a novel, very energy-efficient emission-layer design with improved light-outcoupling concepts, leading to this breakthrough,' explained Sebastian Reineke of the Institute of Applied Photophysics (IAPP) at the Technical University of Dresden, one of the paper's authors.
'The potential of the devices is obvious when one considers that even at the very high brightness of 5,000 candelas per square metre, a power efficiency of 74 lm/W is obtained,' added his colleague, Karl Leo. 'Thus high-intensity illuminations at very high efficiencies are possible as well.'
The researchers believe that, with further research, they will be able to create white OLEDs with an efficiency of over 100 lm/W, while also bringing down the costs of the devices. 'This could make white-light OLEDs, with their soft area light and high colour-rendering qualities, the light sources of choice for the future,' they conclude.
'These results are at R&D [research and development] level and further developments need to be made, e.g. to achieve a commercially acceptable lifetime,' commented Gildas Sorin, CEO of Novaled, a spin-off company from the IAPP. 'However, the values clearly indicate a major breakthrough and qualify OLEDs for mainstream lighting applications.'