Phosphorescent small molecules

SMOLEDs contain small-molecule emissive materials that can be processed by either vacuum deposition (evaporative) techniques or solution coating. The emissive small molecule may be a fluorescent (singlet excited state) or a phosphorescent (triplet excited state) emitter. 

FIGURE 10.7 Power consumption simulation for a 2.2-in. full-color OLED display using Universal Display s phosphorescent OLEDs, small-molecule fluorescent devices, and polymer OLEDs along with a comparison of the power consumed by an active-matrix liquid crystal display backlight. R G B= 3 6 1, 50% polarizer efficiency, and 30% of pixels lit. (From Mahon, J.K., Adv. Imaging, June, 28, 2003. With permission.)... 

D. B. Calhoun, J. M. Vanderkooi, and S. W. Englander, Penetration of small molecules into proteins studied by quenching of phosphorescence and fluorescence, Biochemistry 22, 1533-1540 (1983). 

If we estimate the time required for S-T mixing and recombination for a radical pair to be 100 ns( and the lifetime of the plvaloyl radical at 31°C to be v6 ps(i5., we can estimate the rate constant for the exit of t-butyl/plvaloyl radicals from HDTCl micelles to be on the order of 10 -10 sec . This Is nicely In line with exit rates of small phosphorescent probe molecules from similar micelle systems. 

By analysis of the quenching of phosphorescence by small molecules at low temperature,... 

Similar improvements by introducing a hole-conductive interlayer have been obtained with many other emitting polymers [42]. Recently, record efficiencies of 67 Cd/A (65 lm/W, respectively) were achieved with a green phosphorescent system using a double injection layer (Fig. 9.17), in which the internal quantum efficiency approached unity [43]. This performance is similar to those obtained with small molecules [2[. 

In 1998, Baldo et al. [15] showed that the efficiency of organic LEDs can be improved by using phosphorescent dyes. In their device, the phosphorescent oactaethyl-porphine platinum (PtEOP) dye was doped into an appropriate small molecule host at a low concentration. This electrophosphorescent device emitted red light with an external quantum efficiency of 4%. 

The record-efficiency of OLEDs is based on small molecules. Their characteristics are often unpublished and protected by patents. Novaled reports on 16% and 19% external quantum efficiencies for red and green phosphorescent OLED, respectively, whereas Universal Display produced a 20% white OLED. 

Y. Hino, H. Kajii, and Y. Ohmori. Red phosphorescent organic fight-emitting diodes using mixture system of small-molecule and polymer host. Jpn. J. Appl. Phys., Part 1,44(4B) 2790-2794, April 2005. 

---