OLED displays

Shibusawa, M. Kobayashi, M. Hanari, J. Sunohara, K. Ibaraki, N. 2003. A 17-inch WXGA full-color OLED display using the polymer ink jet technology. IEICE Trans. Electron., E86-C(ll) 2269-2274. 

The simulation discussed above was based on full color produced by individual red, green, and blue emitters. Other full-color reproduction approaches have been proposed for OLED displays including color from blue emitter by means of energy down conversion fluorescent filter [177], and color from white emitters by means of transmission color filter sets similar to that used in LCD industry [178,179]. Table 1.5 compares the EL efficiency of equivalent white... 

The issue of power consumption of an OLED display panel changing with the information content has not been well addressed in the OLED field. For AMLCD display panel, the power consumption is almost independent of the information content. For an AMOLED or an AMPLED panel, the power consumption is directly proportional to the number of pixels lighting up. For each display pixel, the power consumption is nearly proportional to the level of brightness (gray level). Thus, AMOLED display only consumes the power necessary, without any waste. This effect is similar to the concept of Pay-Per-View developed in cable and satellite TV industries. Two direct consequences of the Pay-Per-View effect are ... 

The power consumption of OLED display varies over a broad range for videos in different subjects and different categories and... 

All these features above make AMOLED especially suitable for portable DVD players, digital cameras, portable TVs, and game players. The discussion in this section also suggests that the performance of a given OLED display can be maximized by proper design of display contents. 

As mentioned in this review, AMPLEDs are especially attractive for motion picture applications. The Pay-Per-View effect in OLED displays reduces power consumption and extends operation lifetime. Motion picture applications also minimize image retention and optimize display homogeneity. AMOLED has been widely viewed as a promising display technology in competing with AMLCD and plasma displays. The dream of using organic semiconductor films for optoelectronic device applications has become a reality. 

NCvd Vaart, EA Meulenkamp, ND Young, and M Fleuster, Next-generation active-matrix polymer OLED displays. Asia display/IMID 04, Digest, 337-342, 2004. 

M Kashiwabara, K Hanawa, R Asaki, I Kobori, R Matsuura, H Yamada, T Yamamoto, A Ozawa, Y Sato, S Terada, J Yamada, T Sasaoka, S Tamura, and T Urabe, Advanced AM-OLED Display Based on White Emitter with Microcavity Structure. SID 04, Digest, 1017-1019, 2004. 

J Wang and G Yu, Performance Simulation of Active-Matrix OLED Displays, Photonics Asia 2004 Light-Emitting Diode Materials and Devices, Beijing, China, 2004, pp. 32-44. 

Amorphous silicon back-plane electronics for OLED displays A. Nathan, A. Kumar, K. Sakariya, P. Servati, K.S. Karim, D. Striakhilev, A. Sazonov IEEE Journal of Selected Topics in Quantum Electronics, 10 58-69... 

Figure 6.16 illustrates the correlation between the graded ITO thickness and the EL peak position. The EL peak of the device shows a clear blue shift from 586 to 547 nm as the thickness of the interposed ITO increases from 20 to 65 nm. Likewise, there is a blue shift in EL spectra from 547 to 655 nm when the ITO layer thickness increases from 65 to 175 nm. It demonstrates an easier device fabrication route for multicolor OLED displays using an anode template with a graded ITO thickness. 

Contrast ratio (CR) of an OLED display is very much dependent on the ambient and the lighting conditions. The actual CR for an OLED display is based on the applications and is different depending on the products such as in-car audio, hand phone, etc. Usually for indoor... 

Although ITO is still one of the most widely used anode materials for OLEDs, other alternatives suited for OLEDs may also be used for making optical destructive anode for high contrast OLED displays using this technique. For example, a multilayer optical destructive anode may be fabricated using other oxide materials, including Sn02, FTO, AZO, IZO,... 

Early displays [8] based on vapor-deposited OLEDs were simple alphanumeric devices. More recently, there have been rapid increases in the complexity of these devices. In 1996, Pioneer Corporation demonstrated a monochrome 64 x 256 pixel OLED display [9] that was subsequently developed into a product and was incorporated into automobile stereos (see Figure 7.2). Today full-color, high-resolution vapor-deposited OLED displays as large as 24" have been developed [10]. 

The aim of this chapter is to give the reader a broad overview of the field of vapor-deposited small-molecule OLEDs. It is beyond the scope of this chapter to cover every aspect of these devices, however key references are given throughout the text for those readers who are interested in delving more deeply into this topic. Section 7.2 describes the key elements of a typical OLED. Alternative device architectures are also briefly described. Section 7.3 describes the typical fabrication methods and materials used in the construction of vapor-deposited OLEDs. Section 7.4 describes the physics of an OLED in addition to the improvement of the performance over time made through advances in device architectures and materials. Section 7.5 discusses OLED displays and Section 7.6 looks at the future exciting possibilities for the field of vapor-deposited organic devices. 

FIGURE 7.2 The world s first commercially available OLED display (1999). The display is manufactured by Pioneer Corporation and is incorporated into automotive stereos. 

Other device architectures include inverted OLEDs. Here the cathode is in intimate contact with the substrate. The organic layers are then deposited onto the cathode in reverse order, i.e., starting with the electron transport material and ending with the HIL. The device is completed with an anode contact. In this case, as above, one of the electrodes is transparent, and light exits from the device through that contact. For example, Bulovic et al. [38], fabricated a device in which Mg/Ag was the bottom contact and ITO the top electrode. The advantage of this type of architecture is that it allows for easier integration with n-type TFTs (see Section 7.5 for a discussion of active-matrix drive OLED displays). 

One of the most obvious markets for thin-film vapor-deposited organic materials is in flat panel displays [123], a market currently dominated by LCDs. Over the last two decades, a great improvement in the lifetime and efficiency of OLEDs have been achieved. OLED displays can already be found in simple applications such as automobile stereos, mobile phones, and digital cameras. However, to exploit the advantages of the technology fully, it is necessary to pattern the OLEDs to form monochrome, or more preferentially, full-color displays. This section will consider the difficulties involved in addressing such displays (either passively or actively) and the variety of patterning methods that can be used to produce full-color displays. 

Each of the techniques described above has unique strengths and weaknesses, and the optimum device structure for commercial full-color displays will also be heavily influenced by the ease with which it can be mass-produced. Currently full-color OLED displays have been manufactured commercially by using two of the above described techniques only, i.e., (a) side-by-side pixels deposited by high-precision shadow masking and (b) using white OLEDs and color absorption filters. 

OLED displays can also be fabricated on flexible substrates [159-161] such as metal foils or plastic. This enables entirely new display features such as conformability, ruggedness, flexibility, and reduced weight. 

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