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."
