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Sharing technical expertise to solve the manufacturing challenges in producing organic light-emitting diodes (OLEDs), Saint Gobain Recherche (SGR) has partnered with Novaled to create a breakthrough in glass substrates. The development, based on a unique, high-performance metallic anode, demonstrates the feasibility of large-area OLED displays.

Teaming up under a two-year research program, SGR and Novaled have sought to develop basic technologies for high-performance white OLEDs. As a result of their efforts, researchers at SGR have developed a highly conductive transparent electrode.

Trademarked under the name Silverduct, the electrode is deployed as the anode in an OLED topology. It exhibits a surface conductivity up to 10 times better than indium tin oxide (ITO), the standard material employed in these applications.

Traditional ITO-coated glass is limited in its ability to carry current over distances longer than a couple of centimeters. To create large-area OLEDs, the ITO layer needs be layered with a thick metallic grid, which prevents gradients of light emission caused by the resistance of ITO, typically 30 O/sq.

The Silverduct anode specifies a sheet resistance of less than 4 O/sq, thereby accommodating large-area OLEDs while eliminating the need for extra grids. In addition to enabling a larger display, eliminating the metal grid significantly reduces manufacturing costs.

Pairing the Silverduct anode with Novaled’s PIN OLED technology for high-efficiency OLEDs, the partners manufactured OLED samples on much larger surface areas. In essence, the breakthrough makes possible the production of OLED devices measuring up to 100 by 100 cm.

PIN OLED TECHNOLOGY
Based on proprietary techniques and materials, Novaled’s PIN OLED technology initially targeted white OLEDs. It boosts power efficiency and extends the operating life of OLEDs, two areas of great concern.

Performance improvements include an efficiency of 35 lumens/W with a lifespan of 100,000 hours at a brightness of 1000 cd/m². Additionally, the device exhibits CIE color coordinates of x,y = 0,43/0,44 with a color rendering index (CRI) of 90.

Novaled’s OLED takes a stacking approach using red/green and blue fluorescent emitters. The stacking and transport layers are proprietary materials (see the figure). As standard, the OLED employs an out-coupling enhancement film.

Since the technology’s debut, Novaled has further extended the lifespan for top-emission and bottom-emission PIN OLEDs to greater than 1 million hours at a brightness of 1000 cd/m². Addressing demands for RGB active matrix displays, the company has demonstrated blue fluorescent PIN OLEDs with an operating life of 50,000 hours at 500 cd/m² in bottomemission and green phosphorescent PIN OLEDs surviving 100,000 hours at 500 cd/m² in top emission.

PROBLEMS SOLVED
Historically, the primary challenges to OLED product development have been their short lifespan, power inefficiency, and low resolution, relegating their use to small displays only. However, the marriage of Novaled’s long-life, high-efficiency components with Saint-Gobain’s Silverduct anode appears to have removed these hurdles.

According to Didier Roux, VP of Research at Saint-Gobain, “Combining the advantages of Novaled PIN OLED technology with our electrode, we achieved lab samples with an increased efficiency of +30%. The lack of a metallic grid makes the whole processing much easier.”

These solutions couldn’t come too soon. According to a January 2008 report by industry analyst firm NanoMarkets, the market for printed and organic signage will hit $2.5 billion by 2015. Electrophoretic, electrochromic, cholesteric liquidcrystal, field emission, and OLED displays, plus electroluminescent materials and emissive carbon nanotube technology, will significantly impact a wide range of signage markets, from outdoor billboards to point-of-sale systems.

These predictions plus the strides made by Novaled and SGR translate into numerous opportunities for OLED manufacturers and the companies that support them. If all goes as foreseen, the OLED market will be bright as well as large.