OLEDs could be used for power-efficient large area light sources

Paul Boughton
Philippe Christou, Michael Elwell and Bernhard Sailer believe that increased applications and energy efficiency mean that OLEDs will be among the next generation of general purpose lighting

Following their discovery more than 50 years ago, organic light emitting diodes (OLEDs) have since been viewed as holding significant benefits, particularly for use in display technologies. Because OLEDs are classed as light emitters, they do not require a backlight. This means that battery operated products with OLED fitted displays have the potential to perform better and even outlive their LCD equipped counterparts. More recently, with the EU's objective of cutting at least 20 per cent in CO2 emissions by 2020 and studies by the JRC showing a huge potential for saving energy by creating better energy efficiency forming the backdrop, the lighting industry has gradually started to regard OLEDs as promising alternatives to conventional light sources.

While solid state inorganic light emitting diodes (LEDs) comprise point light sources, OLEDs could be used for power-efficient large area light sources or general illumination with their revolutionary thin, flat, transparent, lightweight and flexible properties. OLEDs provide brighter, crisper displays than both conventional LEDs and liquid crystal displays (LCDs). They also consume up to 70 percent less energy compared to conventional light sources, meaning that OLED lighting could also help to reduce energy consumption. Hence, it's hardly surprising that OLEDs are increasingly being seen as prime candidates for the next generation of lighting.

The Fast2Light consortium, co-ordinated by Holst Centre, brings together a group of 14 companies, research institutes and universities, with the objective of demonstrating that high quality and cost-efficient lighting foils are the future for lighting and signage applications. The project, which is partially funded under the European Union's 7th Framework program as part of the ICT priority, is addressing large area deposition processes for fabricating cost effective, roll-to-roll light emitting OLED foils.

OLEDs are sensitive to moisture and oxygen and require protection from these in order to maintain a longer lifetime. As such, thin film barriers are one of the prerequisites for OLEDs. Having identified this, it soon became apparent to the Fast2Light consortium that measuring the properties of a barrier would be fundamental, as would standardisation of barrier materials.

Within the consortium project, one of the key members, Huntsman Advanced Materials, worked on developing a new barrier material, designed to significantly prolong the lifetime of OLEDs. The high performance, thin barrier coatings which Huntsman developed are now considered as state of the art and have recently been integrated in the world's first flexible OLED system, on a racing car.

In this year's 24 Hours of Le Mans race, the ORECA 01 car from French racing team ORECA-Matmut used new rear view mirrors with an integrated flexible OLED on the back. The OLED itself was provided by Holst Centre. The integration of the rear view mirrors was made possible due to the special process developed by Huntsman, allowing its Araldite resins to bond and mechanically protect the OLEDs without compromising their light emitting capabilities.

By integrating OLEDs into composite parts and combining the advantages of durable composites with the properties of thin, flexible, large surface OLEDs, a range of new generation lighting ideas for the racing industry are just starting to form. For example, on the dash board, side pods or front of the face car, warning lights, leaders lights and brand names could potentially be displayed. And for racing equipment, OLED light sources could be added onto flat carbon surfaces; for example on information panels on pit walls and on trailers, allowing stewards to move cars quickly into the gravel trap at night.

In encapsulation technology and moist barriers for flexible electronic devices, Huntsman and its partners are among the few who are able to make flexible OLED lighting and signage devices. The integration of OLEDs on a racing vehicle represents a great success; heralded as the most successful benchmark projects to date. Holst Centre is now applying the results of this successful integration to its future research activities in furthering encapsulation technologies and moist barriers for flexible electronic devices.

The topic has been the subject of European research for some time now. In 2004, the OLLA - Organic LEDs for Lighting Applications - Integrated Project, was established to gather and focus European expertise in OLED lighting to jointly realise a high brightness, high efficiency flat light source component and demonstrate its use in ICT and next generation lighting applications. The project's major challenge was to address the combination of size, lifetime and efficiency of OLEDs without compromising on the white colour.

Within the timeframe of the OLLA project, many materials, OLED stacks and processes were developed and large sized lighting tiles were successfully demonstrated. When it ended, the project had also achieved its original goal and was able to demonstrate the basic technology for a white OLED light source. The source, which had an efficiency of 50.7lumen/W, had an initial brightness of 1000cd/m2 and was thought to have a lifetime well in excess of 10,000 hours.

OLLA was the first and largest European research project on OLED lighting. Now, a number of similar European research projects on OLED lighting have started, including the Fast2Light project, TOPAS, CombOLED, Light InLine and OLED100.EU, to name a few.

The overall goal of OLED100.EU is to develop all the necessary technologies forming the basis for efficient OLED applications for the general lighting industry in Europe. OLED100.EU is focusing on delivering OLEDs with twice the efficiency, 10-times the operational lifetime and 10-times the substrate size. OLED100.eu is aiming to create an OLED light source measuring 1 x 1m which has an efficiency of 100lumen/W and a life expectancy of 100,000 hours. A further target has been set in order to commercialise the technology, producing such a device for EUR100/m2.

Having proved its value within the demanding conditions of car racing and with the weight of the industry joining forces to progress its development, it won't be long before we start to see OLEDs taking their rightful place in general purpose, mass market lighting applications.

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Huntsman Advanced Materials is based in Basel, Switzerland. www.huntsman.com/advanced_materials. Huntsman is a member of the F2L project to develop barrier and encapsulation technologies of OLEDs.

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