Materials for Organic Microcavity LED Displays

Jordan et al. have developed a white organic LED technology also based on the Alq/TAD system.37 The blue component of the spectrum is augmented by introducing a thin layer of a blue-green emitting material between the Alq and the TAD. The use of a dye-doped Alq layer in the device adds to the red component of the combined emission spectrum. In this manner, efficient (0.7% external quantum efficiency) and bright (4750 Cd/m2) LEDs have been fabricated with emission colors that are close to white. 

FIGURE 4.13. Normalized electroluminescence spectra of Alq/NAPOXA/TAD LEDs as a function of NAPOXA thickness x (in X). In the inset is shown the fraction of the total LED light output originating in the Alq as a function of x together with a fit to the data points. 

FIGURE 4.14. Device structure of LEDs with multiple emitting layers. 

FIGURE 4.15. Electroluminescence spectra from two noncavity devices with the structure shown in Fig. 4.14b. The thicknesses of the undoped Alq layers in the two devices are 20 nm and 30 nm. 

The effects produced by a planar microcavity on the electroluminescence characteristics of organic materials have been described. A number of organic and polymeric semiconductors have been employed by various groups in studies on microcavity LEDs. However, for detailed descriptions, three categories of emissive materials have been considered undoped Alq, Alq doped with 0.5% pyrromethene, and Alq+NAPOXA. Alq has a broad free-space emission spectrum spanning the 

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