Color phosphorescence devices

By altering the structure of the ligand attached to the iridium, the color of the emission can be tuned, and red, green, and blue phosphorescent devices have been prepared [39]. 

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.)... 

In addition to the incorporation of fluorescent chromophores in PF, phosphorescent moieties have been widely used to copolymerize with fluorene or as pendent group in PFs for color tuning (via the selection of ligands chelated to heavy metals) and performance improvement. The ability to enhance device performance via phosphors is because strong spin-orbit coupling (resulting from the inclusion of heavy metal atoms in the phosphor structure) can efficiently utilize triplet excitons for electroluminescence and theoretically there are three times as many as triplet as singlet excitons. 

Another very effective method of preventing triplet-triplet annihilation was reported by Burn and coworkers using dendrimer ligands to surround and protect the iridium core. The color of the emission can be tuned by altering the core of the molecule and the properties of the material controlled by variation of the dendritic structure [42]. For example, the iridium dendrimer 13 has an external quantum efficiency of 10.4% in a single layer device. These phosphorescent dendrimers also have the additional advantage that they are sufficiently soluble and massive enough to be spin-coated from solution. 

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