14 OLEDs
Organic growth
OLEDs are tipped to be the
cheap due to production costs. CDT’s fabrication
method, on the other hand is simply printed onto
next big thing in display the substrate.’
technology. Greg Blackman
The advantages of OLEDs are that they’re
emissive and require no backlighting, which in
assess the progress of these
turn makes them thin, light and a lower power
consumer than equivalent backlit LCDs. There
light emitting polymers is no colour shift or degeneration from different
viewing angles and the devices can also be switched
on and off quickly, making them potentially able to
The development of Organic Light Emitting deliver more satisfying video content.
Diodes (OLEDs) by Kodak in the 1980s and the Currently, portable devices with low power
Currently, OLEDs are produced commercially for small
subsequent technological advances made over consumption and low weight, such as mobile
displays, such as on this digital radio. Image courtesy
the ensuing years has led to a great deal of hype phones or digital cameras, have been the first of Pacer.
surrounding the light emitting polymers. OLEDs major application to exploit the benefits of OLED
have long been touted as a replacement for Liquid over LCD displays. lifetime, the OLED needs to be tested to failure.
Crystal Displays (LCDs) as the dominant display One of the biggest advantages of OLEDs is But Cobb notes that, invariably, by the time testing
technology, promising a greater range of colours, their flexibility in terms of substrate used. ‘OLEDs is complete the technology has progressed to the
improved power efficiency, and potentially cheaper can use a variety of substrates instead of the rigid extent that the product in question is obsolete.
manufacturing methods. Many OLED providers glass we are familiar with in flat panel displays,’ Kirk Lim, displays product manager at Pacer,
believe that this day is imminent and a lot of the comments James Owens, assistant sales manager adds: ‘Certifying the lifetime of a display also
big television manufacturers are developing OLED- for the systems division at global company depends on how accelerated testing is carried
based large screen TV prototypes. In January 2009, Hamamatsu Photonics. ‘The organic films that out and the amount of time each of the colour
Sony CEO Howard Stringer outlined plans to start emit the light can be applied onto materials polymers are in use.’ A typical movie, for example,
selling 20- to 30-inch OLED flat panel TVs before such as flexible plastics, fabrics, and can even be would use the whole gamut of colours at intensities
the end of the year, and Samsung are also pushing designed so that the OLED is transparent.’ Flexible way below maximum for much of the time. A full
ahead to move to OLED displays. substrates would allow the display to be folded, brightness, white screen would be a rarity.
Broadly speaking, OLEDs are solid state devices bent or rolled up and OLEDs could potentially Pacer’s Cobb says: ‘The lifetime values for
utilising light emitting polymers. They comprise form pull-down projector-type screens, as well OLEDs used in consumer goods, such as TVs
of two or more distinct organic molecules or as being printed onto clothing to enhance high- and laptops, need to be around 10-15,000 hours,
polymer film layers sandwiched between electrical visibility jackets, or onto curved surfaces for use in values which are very achievable, at least on a
connections and mounted onto a substrate. Light is the automotive industry. small scale.’ He suggests that in three to four years
emitted when an electrical current passes through OLED polymers emit light at temperatures as the majority of laptops will be manufactured with
the device, with the colour determined by the type low as -40°C making the technology particularly OLED displays.
of organic molecule used. attractive to certain military applications, for But Cobb does make a distinction between the
om
There are two licensed commercial versions instance. However, the hotter the polymer gets, the lifetimes required for consumer goods and those for
currently produced: those using Kodak’s fabrication shorter the lifetime, and it is insufficient lifetime industrial equipment: ‘For industrial and medical
ooptics.c
process, where the OLED is sandwiched between values that are still considered the main problem equipment, lifetimes will need to be around
ectr
two glass sheets; and those licensed from with the technology. 50,000 hours for producers of this equipment to
.el
Cambridge Display Technology (CDT), which use ‘To make flat panel OLED TV screens a use OLED displays, as the usage is so much higher
www
an inkjet method allowing OLEDs to be printed success, the films will probably need to have than consumer goods, and the product life is so

onto a flexible substrate of varying size. double the current typical lifetime values,’ much longer. The technology is verging on the
‘Kodak’s method is three or four years more says Owens. Hamamatsu makes the C9920 50,000-hour mark (monochrome only), but it
ch 2009
advanced than CDT’s and the vast majority Photo-Luminescence Absolute Quantum Yield will be another three to five years before industrial
of commercially available OLED displays are measurement device to aid research into OLED products are operating using OLEDs.’
manufactured using this,’ explains Martin Cobb, lifetimes. Alexandra Gay, marketing and communication
f
ebruary/mar
product manager at Pacer, an international supplier The production of a long-life, full-colour display specialist at UK-based Cambridge Display

of optoelectronic, display and laser solutions. is hampered by the fact that the RGB polymers do Technology (CDT), which manufactures its
‘Kodak’s fabrication method lends itself very not degrade over a linear period, and also by the Polymer OLED (P-OLED) using inkjet processing,
o
optics
well to small, monochrome displays, but it takes difficulties with performing accelerated life testing. comments: ‘CDT has achieved rapid progress in
ectr
el
place under vacuum and will therefore never be In order to certify the product as having a specific P-OLED material lifetimes. At current lifetime
EOfeb09 pp14-15 OLEDs.indd 14 17/2/09 16:45:14
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