Phosphorescent OLED device architecture

The luminous efficiency of OLEDs can be improved Imther by use of phosphorescent emissive materials. Incorporated into OLED devices starting in the 1990s, phosphorescent dopants have a potential to achieve 100% internal quantum efficiency. We will describe materials and architecture developments of phosphorescent OLED devices in Section 14.4. Finally, we discuss the future outlook of the OLED technology in Section 14.5. 

Architectures and Performance of Green Phosphorescent OLED Devices... 

This section covers the background information for OLED devices that applies to both fluorescent and phosphorescent devices. In addition, materials and architectures specific to fluorescent devices are discussed. Phosphorescent structures are described in Section 14.4. 

At the early stage of phosphorescent OLED development, red triplet devices often employed a conventional architecture— HTL, EML, and ETLs were placed between the electrodes. Additionally, a HBL was often inserted between the EML and the ETL. The general structure of a red phosphorescent OLED is shown in Figure 14.30. The device may also include a HIL and an exciton/electron-blocking layer (EBL) placed on the anode side of the EML. The effect of the blocking layers on device performance and criteria for material selection for the layers in triplet OLEDs will be discussed in Section 14.4.2.2. The structures of materials commonly used in red phosphorescent OLEDs are shown in Figure 14.31. 

TCTA, TPBI, and SBFK were used as model cohost materials to demonstrate that mixed EML architecture offers a significant advantage in device performance compared to the conventional neat-host devices and can be used as an alternative approach to the design of triplet OLEDs. The most important feature of this architecture is that the simple variation of the cohosts ratio "tunes up" the location of recombination in the mixed EML, allowing simplification of required properties of the materials used in phosphorescent OLEDs. 

Device architectures of white OLEDs using phosphorescent emitters can be similar to the architectures described in Section 14.3.5. The white color can be generated by the simultaneous emission of light from multiple emitters in... 

Another example of a white phosphorescent OLED with triple-doped EML was demonstrated recently. The device architecture was similar to that described above however, the material structures used were not disclosed. At lOOOcd/m the white triplet OLED showed 251m/W, CRI index of 78, and CIEx,y of (0.39,0.44). At lOOcd/m, the device power efficacy reached 301m/W, and with outcoupling enhancement the total power efficacy increased to 511m/W. 

Good OLED performance, even in devices with advanced architectures, cannot be achieved without the use of efficient and stable phosphorescent... 

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