Before the inorganic LED manufacturers even have their first product ranges designed, tested and manufactured for widespread exploitation of the domestic and commercial lighting markets, the next pretenders to the throne are already on the way. Organic light emitting diode technology (OLED) will prove a serious and possibly disruptive competitor to the conventional high brightness inorganic LED.
OLED technology made its appearance in the flat panel displays market in recent years with applications in MP3 players, household appliances and mobile phones. Very recently, OLED has made its debut into the domestic TV market, with rave reviews about its image quality, brightness and colour range.
With the markets originally pioneered by Kodak with its vacuum-processed small molecule technology, and latterly expanded by Cambridge Display Technology with its solution processable polymer OLED (P-OLED) materials, OLEDs are poised to start the fight back against the dominance of LCDs in the conventional flat panel display marketplace. What has been less obvious to the market at large is the commercial convenience of using OLEDs to create lighting products for consumer and commercial applications.
At the heart of this OLED lighting revolution is the desire of the inventors to break the mould – to get away from the dogma of ‘like replacing like’, where the lighting world has been gripped by the need to replace incandescent lamps with form, fit and function replacement solid state LED lamps just to save a few watts of power. Instead, OLED designers want to change how we light the world.
Incandescent lamps and LEDs are point sources of light, so products and lighting designs today are mostly centred on making best use of bright spheres of light. OLEDs are inherently area sources of light, and with solution processable variants ideally suited to printing large areas at low cost, completely new lighting concepts are facilitated. Initial products are likely to be “lighting tiles” built on glass substrates, with blocks of light of 200x200mm up to 600x600mm, followed by ‘electronic wallpaper’, where complete walls or ceilings will be covered by OLED materials printed or otherwise deposited onto flexible substrates using roll to roll production techniques.
Lighting products may range from ‘one pixel displays’ of constant colour through to pixelated, multiple colour panels that can change colour and brightness according to your mood or the task to be performed in the vicinity.
OLED devices can also be fabricated as transparent devices, leading to the intriguing concept that normal windows could be coated with these OLED materials such that at night they are transformed into the light sources to illuminate the same rooms, doing away with all need for supplemental lighting devices.
Much of the research and development to underpin these ideas and turn them into real world products is taking place around the UK.
Ultra-efficient lighting is a topic of national strategic importance, and the British Government is funding development across the board, in multiple technologies across the spectrum of materials, processes and device architectures to help identify the winners in this global race.
World-class production of OLED materials, at companies such as CDT in Cambridge and London’s OLED-T, is supplemented by research activities at Universities including Durham, Cambridge, Hull, Oxford, St Andrews, Imperial, Sheffield and Manchester amongst others.
In the UK, the Technology Strategy Board is the primary funding body responsible for supporting innovation in industrial technology development and exploitation.
A specific example in OLED lighting is project TOPLESS (thin organic polymeric light emitting semiconductor surfaces), funded with a £3.3m grant over three years. Project partners are Thorn Lighting, Sumation (the joint venture materials company formed by CDT and Sumitomo Chemicals) and the University of Durham, and the objective is to research and develop organic white light emitting polymers and devices.
“My team comprises organic chemistry and physics research scientists focussed completely on commercially viable lighting product,” said Dr Geoff Williams of Thorn Lighting, project manager for TOPLESS. “Since beginning, we have developed high quality, white light, single polymers with a colour temperature approaching 4,000K. Small area test devices have demonstrated lifetimes of 15,000hrs at 500cdm2. This is excellent progress and the coming months will see larger area single pixel devices being assemble with these materials.”
Device efficiencies are also promising with values well in excess of the expected 5 lm/W targeted for the first year. “Novel techniques are being investigated which it is hoped will allow 15 lm/W to be realised by the end of year two,” said Williams. “The roadmap for development demonstrates P-OLED product efficacies approaching fluorescent T8 luminaires by 2011.”
As well as driving material efficiencies up, project TOPLESS is also seeking to simplify and cost reduce the present structure.
According to Thorn’s Williams: “The technical drive over the next two years is to minimise the number of deposited layers between the electrodes. Today there are three solution deposited layers amounting to a total organic layer thickness of approximately 100nm. Reducing this would lead to even simpler manufacturing assembly processes and improve uniformity of the light across the whole device.
The team continuously strives to develop alternatives to the reactive metal cathode and ITO anode structures, replacement of either one or both will result in distinct benefits for the P-OLED devices. Material and device development has also been guided by product marketing input, steering this development towards rapid commercial exploitation.”
TOPLESS is one of many collaborative research projects in this technology area funded by the Technology Strategy Board. The project partners are encouraged to access the outcomes from other funded projects with the objective of encouraging UK-wide communal exploitation of IP for the benefit of UK plc.
The UK Displays and Lighting Knowledge Transfer Network plays a primary role in spreading the word about these technology activities and creating consortia in the UK and beyond.
The UK is at the forefront of development in OLED lighting, but it is certainly not alone. Many companies around the world are developing OLED lighting projects. European projects such as OLLA, with 24 partners including Philips, Osram, Novaled, Aixtron and Merck show the depth of interest the EU has in this nascent market area.
On March 19 this year, EW reported that Osram have demonstrated 46 lumens/Watt from their ‘warm white’ OLED multiple layer, glass-based, vacuum processed small molecule lighting tiles with a brightness of 1,000cd/m2 and lifetime of over 5,000 hours.
OLED lighting is on its way with the potential to outshine its solid state LED competition by virtue of its potential for simplicity of construction and low cost of manufacturing.
Chris Williams is a director of UK Displays & Lighting Knowledge Transfer Network