German researchers have achieved encouraging results in research on organic light-emitting diodes (OLEDs), giving rise to the hope that European companies might someday capture a larger portion of the flat-panel-display market. Currently, this market is dominated by suppliers from Asia. The total display market is estimated to be about $75 billion and is expected to grow to $100 billion in 2008, with cathode-ray tubes (CRTs) progressively losing their share to thin-film-transistor (TFT) displays.
As a component supplier, Merck (Darmstadt, Germany) shares about 70% of the world market for liquid crystals, mostly shipped to Asia for TFT production. But OLEDs will compete with liquid-crystal technology as the basis for next-generation flat-panel displays. For this reason, a European collaboration has been formed to further develop OLED technology and flat-panel-display manufacturing techniques, so that European companies could also manufacture complete OLED-based displays.
The project, called F & E Initiative OLED 2015, has recently been launched at the Congress on Optical Technologies (Feb. 22; Berlin, Germany) by Philips (Eindhoven, The Netherlands), Osram Opto Semiconductors (Regensburg, Germany), Samsung SDIG (Berlin, Germany), and Merck, and will be sponsored by the German ministry for education and research. The four companies plan to spend more than €500 million (US$647.5 million) and will be supported by the ministry with another €100 million (US$29.5 million) over a five-year period.
In addition to their use in displays, OLEDs show high potential for lighting. Advanced OLEDs have high efficiency, allow full color control, and introduce a new kind of flexibility into architectural design (via so-called “light-emitting wall paper”). To make such applications feasible, a European research program called Olla (Organic LED for Lighting Applications)—a collaboration between 24 research laboratories and companies in eight countries—was formed in October 2004 with the ambitious goal of creating an OLED white-light source for room lighting with a 10,000-hour lifetime. This project of the European Union complements the U.S. Next-Generation Lighting Initiative and the Japanese Lighting 21 programs already in operation.
Recent research results support this optimism. At the Technische Universität Dresden and Novaled (both of Dresden, Germany), together with Universität Kassel (Kassel, Germany), researchers succeeded in achieving an external quantum efficiency of 19% using the green-emitting phosphorescent dye tri(phenylpyridine)iridium doped into two organic host layers, one showing electron conductivity, the other hole conductivity.1 Light emission occurs from both layers. The double-emission-layer concept increases the efficiency and prevents too strong a loss in efficiency at higher current densities—a drawback for earlier OLEDs. Furthermore, the p-i-n diode design of the device allows low operating voltage. The results are a power efficiency of 77 lm/W and an external quantum efficiency of 19% (photons per injected electron-hole pair) achieved at a luminance of 100 cd/m2, dropping to 50 lm/W at a considerably brighter luminance excitation of 4000 cd/m2.
Reaching 110 lm/W Very recently, a world record was demonstrated at Novaled in which a green-emitting OLED reached 110 lm/W at a brightness of 1000 cd/m2. "This value is about two times higher than those obtained by competitors, and about 50% higher than what has been achieved with inorganic LEDs," said Jan Blochwitz-Nimoth, Novaled's chief technical officer. The doped transport layers lead to high power efficiency for red-, green-, and blue-emitting versions (see figure). Other German OLED research centers include Covion (Frankfurt), which was recently taken over by Merck, and Technische Universität Braunschweig. The OLED 2015 project team aims to develop full OLED manufacturing and processing technology, and is open to additional partners. The partnership of Samsung (globally headquartered in Seoul, Korea) is understood by the fact that Samsung sees itself as a "global player" with both research and manufacturing in all important world market regions. Samsung demonstrated a 17-in. OLED display in May 2004. In Berlin, a Samsung-owned CRT production line could also pursue flat-panel-display manufacturing based on OLEDs. A similar global outlook holds for LG Philips, a joint venture of Philips and LG Electronics (Seoul, Korea) and a strong competitor of Samsung. LG Philips showed a 20-in. OLED display in October 2004. Clearly, the European OLED race is in rapid progress.
REFERENCE
1. G. He et al., Appl. Phys. Lett. 85 (17) (2004) 3911.