The Latest Advances Changing the Prospects for OLED Materials

Friday 10 August 2012, Amsterdam

The technology gaps in the OLED industry have not gone unnoticed by the materials suppliers, which have been providing steady improvements in performance. Overall, most clearly needed by the OLED industry are materials used in the functional stack – emitters, hosts, transport and blocking materials, etc. – that enable higher efficiency and longer lifetimes at the right color points to achieve proper color gamut (in displays) or the right color rendering index (CRI) and color temperature (in lighting).

Obviously, US-based OLED materials pioneer Universal Display Corporation (UDC) and its materials partners are at an advantage here, at least with respect to phosphorescent technologies and the superior efficiency that they can provide, and with respect to customization and optimization of auxiliary materials to be used in conjunction with the phosphorescent materials.

However, a breakthrough by an outside firm based on non-phosphorescent (or at least not on iridium metal cores) could be quite lucrative to the inventing firm as well. Breakthroughs in any of a number of other materials could also translate into a significant opportunity.

The Need for Better Blue Emitters

In Lighting: As we noted above, lifetime is still a critical issue for up-and-coming key OLED applications. Some progress has been made on the color and lifetime of a light blue OLED emitter system that may advance OLED lighting . For example, UDC is now actively commercializing a light blue emitter that delivers 70 lm/W luminous efficacy and an operating lifetime of 30,000 hours (to 70% of initial luminance) in an OLED lighting panel.

While this achievement is notable, the industry still has much to be accomplished. First, it remains to be proven that this material can be scaled up at the customer with the same results. Second, even this performance lags behind that required to support a serious business case, i.e., at 100 lm/W and 50,000+ hour lifetimes, for using OLED lighting in general illumination applications.

In Displays: More critically, the lifetime problem has not yet been solved adequately for red, green, blue (RGB) full-color displays, especially with respect to high efficiency deep blue phosphorescent emitters.

In the AM OLED displays on the market today, red phosphorescent emitters are already used preferentially, and green phosphorescent systems are increasingly being adopted as well. But even in the relatively small, relatively short-lived AM OLED mobile computing applications, the blue emitter system is still dominated by a conventional fluorescent system.

Furthermore, there are no real signs that the industry will make the switch to all-phosphorescent any time soon, other than a vague promise by Samsung to adopt UDC’s phosphorescent blue “as soon as it can be qualified.”

The problem is that the larger-area applications like TVs are expected to have much longer product lifetimes than most mobile computing devices, which today makes differential aging among emitter systems a problem for display engineers and consumers alike.

This report expects that the OLED TV industry will need to make a move toward all phosphorescent to allow the technology to establish a strong foothold in the display market. Solving this problem is a materials related issue.

The Need for Bigger Panel Sizes and the Importance of Solution-Processing

Panel size is also getting a lot of development attention. For large-area OLED TVs and OLED lighting to realize their full potential, panel makers need to demonstrate scalability and break into general illumination market(s), respectively. Materials suppliers can seize the opportunity by developing materials that enable an easier shift toward larger areas.

The most promising path to achieving larger areas at lower cost, and the path that many are betting on, involves a transition to solution processing for the fabrication of the OLED layers. Development, and demonstration of the viability of large-area patterning methods, based on OLED materials inks and/or coatings, would eliminate the problem of sag-prone fine metal masks.

While GE (USA) has struggled with its development of printed OLEDs (admittedly on flexible substrates), others have forged ahead with development. DuPont Displays (USA), UDC, and Merck/EMD (Germany) are all betting on solution-deposition, and are actively developing materials compatible with the various solution processing technologies under development. Included in the possible solution-based patterning technologies are aerosol jet printing, ink-jet printing (less advanced), and various other printing or coating methods.

What Ever Happened to Polymer OLEDs?

Printed polymer OLEDs have been in the “development phase” for a very long time now, and this report has become skeptical that they will ever emerge from that phase. In fact, we think it is increasingly likely that the polymer OLED approach will simply be abandoned at some point and replaced with the more promising (and more proven, at this point) solution-processed small molecule approach of DuPont Displays and others.

That said, there is at least one firm – Sumitomo (Japan) – that may prove this assessment incorrect. Sumitomo controls most of the key IP in this sector, and is the only firm still actively (and publicly) pursuing development of applications for polymer OLEDs. There have even been a few signs of hope in the last year:

The firm announced plans to invest modestly in a new materials plant, which we think it could be doing to support a printed polymer OLED TV program at partner Panasonic. It is just as possible, however, that Panasonic will go another way, i.e., toward solution-processed small molecule printing.

Sumitomo has made a strategic shift toward OLED lighting, and plans to start producing its own OLED lighting panels in 2013 for, probably, demonstration purposes and to advance the cause of polymer OLEDs in general. Sumitomo’s goals for lifetime and efficiency are lower than those planned by the “mainstream” OLED lighting industry, but the company is betting that its lower costs, and flexibility, will be an attractive trade-off.

But the key word here is “demonstration.” Polymer OLEDs need to move out of the demonstration phase, and quickly, or get left behind altogether.

Thus, the real question is whether Sumitomo will be successful at finally proving the viability of large panel manufacturing based on printing polymeric materials. Surely, Sumitomo has put more effort into this goal than anyone.