Fluorescent blue dopant

These materials have large band gaps and are thermally stable with high Tg. Details describing the use of these materials will be presented in the section on fluorescent blue dopants. 

Enhancement in the performance of OLEDs can be achieved by balanced charge injection and charge transport. The charge transport is related to the drift mobility of charge carriers. Liu et al. [166] reported blue emission from OLED based on mixed host structure. A mixed host structure consists of two different hosts NPB and 9,10-bis(2 -naphthyl)anthracene (BNA) and one dopant 4,4 -bis(2,2-diphenylvinyl)-l,l -biphenyl (ethylhexyloxy)-l,4-phenylene vinylene (DPVBi) material. They reported significant improvement in device lifetime compared to single host OLEDs. The improvement in the lifetime was attributed to the elimination of heterojunction interface and prevention to formation of fluorescence quenchers. Luminance of 80,370 cd/m2 at 10 V and luminous efficiency of 1.8 cd/A were reported. 

Figure 14.11 shows the progress at Kodak in performance of simple two-layer single-stack white structures based on fluorescent hosts and dopants incorporated into a two-emission layer yellow I blue (Y B) configuration. The performance has continuously been improved, culminating in... 

The triplet-harvesting mechanism was confirmed by efficiency analysis of the BIY device spectra. A blue fluorescent (BE) device was constructed similarly to the BIY except that the phosphorescent emitter was omitted. The blue portion of the spectrum (380-512 nm) of the BE device exhibits 4.9% EQE, indicating very efficient fluorescence. Figure 14.52 shows that devices B Y and BE have nearly identical spectral radiance for the blue component of the electroluminescence. Thus, fluorescence remained the same while the addition of the phosphorescent dopant to the BE device resulted in the appearance... 

Spectra of blue yellow (B Y) harvesting hybrid and blue fluorescent OLEDs. Blue device has the same structiue as B Y except that the yeUow phosphorescent emitter is omitted. Data are taken at ImA/cm. Inset Structure of the yeUow phosphorescent dopant. 

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