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Passive-Matrix

Polymer LightEmitting Displays

Eliav I. Haskal, Michael Büchel, Paul C. Duineveld, Aad Sempel, and Peter van de Weijer Abstract Organic light-emitting devices (OLEDs) have attracted considerable interest in the last five years and are now viewed as an important competitor with liquid crystals for a wide variety of display applications. Current research focuses on the use of small-molecule and polymer materials to make organic electroluminescent displays with both passiveand active-matrix technologies. This article will discuss work on the device architecture for a polymer passive-matrix display application, the stability of polymer light-emitting displays, and the use of ink-jet printing for high-resolution patterning of red, green, and blue light-emitting polymers. Keywords: flat-panel displays, optoelectronic materials, organic light-emitting devices (OLEDs), polymer light-emitting displays (PLEDs), polymer passive-matrix displays, polymer thin films.

Introduction The flat-panel display industry has grown tremendously in recent years based on the success of the liquid-crystal display (LCD) for high-information-content display applications. In parallel, organic light-emitting device (OLED) technology has evolved to the point where it is now viewed as an important competitor with LCDs for a variety of display applications. Indeed, OLED sales are forecast to reach 5.8% of the total worldwide flat-panel revenue by the year 2007.1 This has led to the introduction of OLED research and development programs in at least 100 universities, research laboratories, and companies in the last five years, all working on this potentially disruptive technology. Organic electroluminescent displays are emissive displays, providing certain fundamental advantages over LCDs for highquality, high-information-content video applications. These advantages include a wide (
170) viewing angle, fast display response time (microseconds), broad color range, high (
200
1) dark contrast (the ratio of black to white in dark conditions), and a thin and light display module. With

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this in mind, most of the companies currently working toward the production of OLED displays are focusing on mobile telephones, personal digital assistants (PDAs), digital cameras, camcorders, digital video disk (DVD) players and automotive applications. The first products using OLEDs were produced by Tohoku Pioneer in 1999 for mobile telephones and car radios. Currently, Samsung and NEC Mobile Display are also shipping commercial products, as is Royal Philips Electronics.

Background Organic electroluminescence, or the generation of light by the electrical excitation of an organic material, was first observed in the 1960s with the application of several hundred volts across an anthracene single crystal.2 This early work was improved upon using thin organic films, which led to a voltage reduction to
30 V, but still with a photon/electron external quantum efficiency of only 0.05%.3 An intuitive leap was made in the 1980s by Tang and Van Slyke, who re