Second Wind For OLEDS

Organic light-emitting diodes may not have lived up to the hype that surrounded them in 2000 when promoters proclaimed the imminent arrival of large, flexible displays, but that doesn't mean OLEDs haven't been successful. Only a few years after their first commercial applications, the OLED-based display industry is already worth hundreds of millions of dollars—a ramp-up that developers of any new technology would envy. Building on their earlier successes and learning from past challenges, OLED developers say they are on the brink of a next wave of growth in more advanced applications.

Experts say OLEDs have many inherent advantages over liquid-crystal displays (LCDs), the dominant flat-panel technology on the market today. In OLED technology, polymers or small organic molecules emit light when acted upon by an electric current. Liquid crystals, in contrast, work by orienting themselves in the presence of an electric field to block out light emitted by a backlight.

This difference allows OLED displays to offer less power consumption, higher contrast displays, wider viewing angles, thinner architecture, brighter colors, and faster response times than LCDs, says Terry Nicklin, marketing director for Cambridge Display Technology (CDT), a developer of technology for polymer-based OLEDs. "There is something odd about a technology like LCD, where you are producing a light from a bulky, power-hungry backlight and then filtering out most of that light and wasting it," he says. "That doesn't sound very efficient."

According to Nicklin, OLEDs are off to a robust start. "It has only been about 10 years between the discovery of organic electroluminescence and its first application," he says.

And from that first commercial application—in a 1999 car radio display-the market for OLED displays increased to $520 million in 2005, says Kimberly Allen, director of display technology and strategy for the display consulting firm iSuppli. She expects the OLED display market to hit $740 million this year and $3.5 billion by 2012.

The first big successes for OLEDs, Allen says, have been in MP3 players and secondary graphic displays for mobile phones, uses that draw on the bright colors and high contrast of OLED displays. "These were surprises for the industry and an early foundation for growth," she says.

These applications were based on simple passive matrix display technology. Active matrix displays, where each display pixel has its own transistors, have proven to be more troublesome for OLEDs. Allen points to two early uses: a Kodak Easyshare camera in 2003 and one of Sony's Clie personal entertainment players in 2004. "They were really just tests of the market, and the results were that there were some challenges," she recalls. Specifically, there were problems with the backplanes of the displays and the lifetimes of some of their colors.

Experiences such as these have led some observers to suggest that OLEDs "stumbled out of the gate." Nicklin concedes that the industry's rhetoric got ahead of itself. "People very quickly grasped the idea of some very exotic products like roll-up giant display screens in the office and TVs rolling out of a pen," he says.

Peter Compo, managing director of DuPont Displays, explains that hype is normal for new technologies. "Certainly, the industry five to six years ago was extremely bullish on OLEDs," he says. "It was just an overestimation of what any technology could do. It is very natural to have some people feel very positive and optimistic, and it is very common for reality to lag behind that optimism."

For OLEDs to succeed, they will have to build on the infrastructure established for the LCD sector, Compo argues. "In principle, OLEDs and LCDs are somewhat in conflict or in competition," he says. "A more important point is that OLEDs do not replace the entire LCD value chain. OLEDs replace only part of the LCD value chain." Both technologies, he notes, use a backplane of thin-film transistors. OLEDs replace the front-plane liquid crystals and color filters as well as the backlights.

Paul Breddels, executive vice president of Merck KGaA's liquid-crystal division, says there is room in the displays business for OLEDs and LCDs. "Both technologies will coexist side by side, and the decision about which technology will be used in a display will depend on the application and the specific requirements of the customer," he says.

A dominant supplier of liquid-crystal materials, Merck placed a bet on OLEDs last year through its purchase of Avecia's Covion polymer OLED unit for $65 million. Breddels isn't shy about his enthusiasm for OLEDs. "For the long term, we see OLED technology as a potential new technology that can rival the existing LCD technology," he says.

CDT's Nicklin sees the purchase as a watershed for the OLED industry. "For us, it was a very important signal that the leading LCD supplier was investing in and developing OLEDs," he says.

Since the Covion acquisition, CDT has made some dramatic changes of its own. Soon after that deal, Sumitomo Chemical purchased Dow's Lumation OLED polymer unit. CDT and Sumitomo then formed a joint venture to pool their R&D expertise in OLEDs and to use Sumitomo to manufacture the resulting materials.

The deal has transformed CDT from a mere licenser and developer of technology, Nicklin points out. "It is a very important strategic change for us to be involved in the supply chain for the first time," he says. "Another issue in building up a new technology and getting it established is building a supply chain."

Observers agree that some technical barriers need to be overcome for OLEDs to progress further. Merck's Breddels says OLED developers must improve backplane technologies, costs, production processes, materials lifetime, and power consumption.

Of those challenges, perhaps the most important is the lifetime of OLED materials. Lifetime, as OLED developers define it, is the amount of time it takes for the luminance of the light emitted by the OLED to decrease to half its original value under continuous operation. Too-short lifetime has kept OLEDs out of large full-color displays in products such as televisions and computer screens that are used for many hours.

But companies are continuing to report improvements along this front. For example, CDT recently announced a blue material with a lifetime of about 200,000 hours at a brightness of 100 candelas/m². Two years ago, Nicklin says, the lifetime of blue at 100 candelas/m² would have been only about 35,000 hours. "It is more than enough for all monochrome applications and small display applications," Nicklin says. "What it wouldn't be enough for yet is large-panel televisions."

Another issue facing the nascent OLED industry is which chemistry will underpin the platform's future success: small molecules or polymer-based OLEDs. According to iSuppli's Allen, some 95% of OLED applications thus far have been based on small-molecule materials including substituted perylenes and quinacridones, whereas polymer-based displays, based on materials such as polyphenylene vinylene and polyfluorene, have lagged.

Small molecules got a head start because they are incorporated into displays via vapor deposition, a common electronics manufacturing process. Polymer-based materials lend themselves to solution-based processes similar to ink-jet printing, a technology that isn't fully developed.

Small molecules have more advanced performance properties than polymers do, but the deposition process is expensive and difficult to scale up, DuPont's Compo says. "Over the past several years, there was an awareness that small molecules had excellent lifetime and efficiency properties, but the only way you could use them was with vapor-phase shadow-mask technology," he says. "Using that process to bring small molecules to market is fairly expensive."

To combine the best of what small molecules and polymers have to offer, DuPont has focused its OLED efforts on developing a solution manufacturing process for small-molecule-based OLED displays. "Polymers haven't been ready, they haven't had the performance that is required, and so we have developed the ability to solution-process small molecules," Compo says. According to DuPont, OLED displays using the technology can be 30% cheaper to make than equivalent LCDs.

Similarly, Universal Display Corp. is working with Mitsubishi Chemical on a solution-based process for Universal's phosphorescent materials.

Display manufacturers will soon take another stab at putting active matrix displays in cell phones, iSuppli's Allen says. By the end of the decade, she adds, the first televisions might be incorporating OLED technology.

So, after several years marked by some success and plenty of hype, developers of OLED technology are regrouping and tackling the real-world problems that have prevented OLEDs from reaching their full potential. And they will leave the roll-up pen TVs for another day.