Osram has achieved a significant efficiency result in its push towards practical OLED lighting.
“After only two years of development, Osram has achieved record values in the laboratory for organic light emitting diodes in warm white,” said the firm. “With an efficiency of 46 lm/W the organic light emitting diodes for lighting applications (OLED Lighting) have a brightness of 1,000cd/m² and last more than 5,000 hours.”
Conventional power LEDs are well established on the fringes of lighting, but cost projections suggest they are unlikely ever to displace light bulbs and fluorescent lamps through market forces alone.
However, if efficiency and lifetime can be improved, OLEDs could do it as their structure lends itself to low-cost mass production.
The flat sheet form of OLEDs matches well with both standard 600mm office lighting units and the area emitting effect achieved by architectural up-lighters. And, unlike most fluorescent technology, OLEDs are fully dimmable.
The Osram OLED is a 10x10cm tile with a light output of between 30 and 50lm. The firm has pulled out all the stops to hit 46 lm/W – particularly in fashionable, but generally less efficient warm white – putting this fledgling technology level with the bottom of established fluorescent fittings in efficiency terms, and well above the 12 lm/W achieved by normal light bulbs.
“Ours emits a homogeneous warm white, with a stable colour over brightness,” Dr Karsten Heuser, director of OLED lighting technology at Osram told EW. “We have scaled it up to 100cm2 to see if it could be transferred to a larger area. This is an intermediate step to prove it is scalable. Another development topic is to find the limits of how large a panel could be made.”
The basic technology in this emitter is vacuum-processed small molecule OLED, as opposed to printable polymer OLED.
“It has a transparent anode on glass, a reflective metal electrode on the back, and an emitter achieved by casting red, green and blue dopants in a matrix material,” said Heuser. “We are focussing to achieve in future very cost-effective processing of this technology.”
OLEDs degrade rapidly in the presence of oxygen and water vapour. Heuser said the firm is using an undisclosed encapsulation process to block these – leading to the 5,000 hour life to half brightness.
For ease of manufacture, installation, and robustness flexible emitters are desirable, but the whole OLED industry is still looking for effective vapour-blocking barrier layers.
Heuser said that his organic layers are flexible and suitable for flexible substrates but “the pre-requisite is sufficient barrier properties and I don’t see that it will be reached in the short term. We need a certain shelf-life and I have not seen more than five or six years shelf life.”