Organic Light Emitting Diodes

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5 Matrix types of OLEDs, Products An OLED is a current-driven device. That is, the intensity of the output light is directly proportional to the electrical current flow through the device. An OLED display, therefore, requires the control and modulation of electrical current levels through individual elements (pixels) in order to display text or graphic images. There are two types of OLED display architectures: passive matrix and active matrix. In a passive-matrix OLED display, the columns provide the data signal, and the rows are addressed one at a time. The current flow through a selected row is necessarily pulsed to a level that is proportional to the total number of rows in the display. This instantaneous current requirement places a restriction on the size and resolution of the passive matrix design. This restriction is removed in an active-matrix OLED display, where each individual pixel can be designed to switch on or off within a frame time. As a result, the device does not suffer the resolution limitations or the high-instantaneous-current requirements of a passive-matrix design. The size and resolution of these displays are determined by practical considerations such as the constraints of the substrates rather than the OLED component. Because the pixel architecture and electrode geometry for the OLED element are already defined on the substrate, the fabrication of the OLED component is straightforward. The cathode is continuous over the entire display area, requiring no patterning. In 1998 Pioneer put on the market first commercially available passive matrix OLED displays in car radio CD-players (Fig. 20). Figure 20: 2004 range of Pioneer car radios ; left - Pioneer DEH-P 6600 with blue OLED display (280$), right - Pioneer DEH-P 8600 with full color OLED display (550 $) These small molecule based displays were also found in Motorola cellular phones by 2000. Recently also mobile phones from other manufactorers came on market, with external 256 colors OLEDs as complement to bigger internal LCDs like in Samsung presented below (Figure 21). In 2003 Kodak introduced a digital camera incorporating the first commercially available active matrix OLED display. After Motorola Figure 21: a) Samsung SGH-E 700 b) Kodak EasyShare LS633 (120.000 SIT) 14
Nearby Future a) Big screens - The technology will provide competitive full-size computer displays and flat-panel TV screens that consume less power than possible with flat panel technologies available today. A prototype of world's largest (till now) - 20" OLED full color display, WXGA (1280x768) with Low power consumption driven by Amorphous Silicon TFTs has been presented in 2003 (Figure 22) by Chi Mei Optoelectronics Corporation (CMO) from Taiwan. Figure 22: Technical details: The 20-inch prototype is a top-emitting full-color active-matrix display. It has WXGA resolution (1280 x 768 pixels) and a power consumption of 25 Watt at a brightness of 300 cd / m² (its desktop display brightness, can exceed 500 cd/m2) [19]. b) FOLEDs - flexible OLEDs [7] are organic light emitting devices built on flexible substrates (Fig. 23). Flat panel displays have traditionally been fabricated on glass substrates because of structural and/or processing constraints. Flexible materials have significant performance advantages over traditional glass substrates. For the first time, FOLEDs may be made on a wide variety of substrates that range from optically-clear plastic films to reflective metal foils. These materials provide the ability to conform, bend or roll a display into any shape. This means that a FOLED display may be laminated onto a helmet face shield, a military uniform shirtsleeve, an aircraft cockpit instrument panel or an automotive windshield [20]. Figure 23: FOLED for DARPA, courtesy Universal Display FOLEDs will also generally be less breakable, more impact resistant and more durable compared to their glass-based counterpart [7]. c) <strong>Light</strong>ning applications - The rapid progress in efficiency and performance demonstrated by OLED technology over the last decade has caused many companies to consider OLEDs as a potential solidstate light source for lighting applications. In terms of application potential, OLEDs nicely complement inorganic LEDs - a technology more often associated with solid-state lighting (SSL). In particular, since inorganic LEDs are bright point sources of light, they are naturally suited for applications such as spot or task lighting that require spatial control over the illuminating beam. In contrast, OLEDs represent a diffuse source of light and so are naturally suited to large area generallighting and signage applications where, for instance, fluorescent lighting is used today. 15
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Organic Light Emitting Diodes

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