Tandem OLED device

Tandem OLED Devices 14.3.6.1 Tandem Device Architecture... 

Although the basic concepts described concerning the microcavity effect have been applied in the present work to bottom-emission OLEDs and specific materials only, they are general and will remain true whatever the materials used in the device (i.e. pwlymer-based), and for other device structures (such as top-emitting-OLED, tandem-OLED, etc.). 

Although stability could be obtained by the tandem structures where each EL stack is white-emitting, it is difficult to obtain high efficiency. The primary reason for the low efficiency is the fact that it is nearly impossible to optimally position both of the identical emitting zones within the OLED structure with respect to the reflective cathode. Taking this into consideration, the following section describes the fabrication of an efficient and highly stable tandem white device. 

Recently, a tandem (or stacked) OLED structure was developed in order to improve luminous efficiency and to increase lifetime. This was accomplished by vertically stacking several individual electroluminescent (EL) units, each of which comprise a HTL EML ETL, and driving the entire device with a single power source. The schematic structure of the tandem device is shown in Figure 14.19. 

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