Add-Vision’s printed P-OLED technology offers many of the attractive characteristics of mainstream OLEDs, but is much easier and cheaper to manufacture. The company developed a doped P-OLED LEP ink that’s specially formulated and doped with additives and transport materials.
The additives enable low-voltage charge injection and high-efficiency radiative recombination in the luminescent polymer without the need for unstable, vacuum deposited metal electrodes. Furthermore, the film is less sensitive to high-throughput variations that are common in vacuumdeposition approaches.
The Add-Vision structure uses air-stable printable cathode materials that enable low-voltage operation, high power efficiency, and uniform emission. Simultaneously, these materials are printable in air and compatible with the low-temperature handling of flexible substrates (Fig. 3).
FLEXIBLE OLED DISPLAYS IN VOGUE
An exciting trend is the AM OLED’s move to flexible displays. “Consumers are attracted to flexible displays and devices not only because they are innovative in design, but also because they provide enhanced functionality,” says Chris Schreiner, senior user experience analyst at Strategy Analytics.
UDC demonstrated a 4-in. diagonal prototype using AM OLEDs. Designed for the military and funded by the U.S. Army’s Communication Electronics Research Center, the device was fabricated in collaboration with LG Display and L-3 Communications’ Display Systems Division as a complement to the work ongoing at ASU (Fig. 4). UDC is also working on a touchscreen version of the display.
At this year’s CES, Sony demonstrated a flexible AM OLED display prototype called Flex OLED, in the form of a Sony Walkman bracelet. Sony believes the product could be a future electronic ink (e-ink) reader. Samsung is also bullish on flexible OLED displays, saying it will double production of OLEDs this year and next year. It has made 2 million OLED panels so far and indicated that it will be able to commercialize such a display by next year.
TURNING ON TO TOLEDS
Transparent OLEDs (TOLEDs), which can be PM or AM devices, produce a white light output. They only have transparent components—the substrate, cathode, and anode. When turned off, they’re up to 85% as transparent as their substrate, as shown by a 12-cm prototype TOLED panel from Philips (Fig. 5).
When a TOLED is turned on, it allows light to pass in both directions. This is useful for heads-up displays, light partitions (nearly invisible by day and a pleasant diffused light at night), mood lighting, light canopies, automotive windshields for navigation and warning systems, and architectural windows. Companies developing TOLEDs include Osram Opto Semiconductors, Philips, and UDC. Prototype TOLEDs are expected to emerge within a year or two.
Using OLED technology for lighting is a major goal of the U.S. Department of Energy (DoE), which is funding the industry to develop energy-efficient products for myriad lighting applications. The DoE estimates that by 2016, white-light OLEDs could save well over $20 billion in electricity costs worldwide and more than 9 million metric tons of carbon emissions from the U.S. alone.
Last year, UDC achieved a record power efficacy rating of 102 lm/W at 1000 cd/ m2 from a white light source, using the aforementioned UniversalPHOLED technology. The DoE last year awarded the company $1.9 million to accelerate the development of white OLED lighting products. UDC also licensed its UniversalPHOLED technology to Konica Minolta for use in Konica’s white OLED lighting products.
An integrated research project launched by the European Union (EU), dubbed OLED100, will look to achieve OLED efficiencies of 100 lm/W and lifetimes of more than 100,000 hours from a chip unit area of 100 by 100 cm at cost of 100 €/m2 or less. This project follows the EU’s successful Organic LEDs for Lighting Applications (OLLA) program, whose membership includes leading European electronics manufacturers as well as research institutions and universities.
One such member, Osram Semiconductor AG, last year demonstrated a 10- by 10-cm OLED tile with a light output of 30 to 50 lm/W at 1000 cd/m2 and 5000 hours of lifetime. This intermediate step in Osram’s work proves that OLED whitelight output can be scaled upward from the lower levels achieved previously. Osram employed a basic vacuum-deposition technology that uses small molecules instead of printable polymers (Fig. 6). That output was later increased to 60 lms/W thanks to a joint effort with BASF AG.
Novaled AG achieved light power efficiency levels of 35 lm/W at 1000 cd/m2 and lifetimes of 100,000 hours using a white stacked structure that connects individual red, green, and blue emission units or multiple white emission units in series. The p-i-n structure comprises proprietary materials (Fig. 7). The emission color can easily be tuned to the equal-energy white for display applications by selecting the emitting materials and varying the thickness of the transport layer.
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