Efficient Polymer EL Devices
-RGB emission by phosphorescent polymers-
Fig. 1 Picture of fabricated polymer EL devices
STRL has developed new organic electroluminescent (EL) devices that use phosphorescent polymers. These EL devices for the three primary colors (RGB)* are highly efficient; in particular, they currently have the world's highest quantum efficiency for polymer devices in the case of R (red) and G (green).
The aim is to use these polymer EL materials to create a foldable, flexible display. In comparison with small-molecule EL materials currently under development, polymer EL materials have greater flexibility, but lower quantum efficiency and shorter lifetime. The EL materials were developed with a new process (phosphorescence) using a novel polymer structure instead of the conventional process (fluorescence) to obtain highly efficient electroluminescence. While the maximum quantum efficiency of fluorescence is 5%, it is theoretically feasible to obtain four times this efficiency, that is 20% quantum efficiency, with phosphorescence.

Table 1 Current performance of polymer EL devices
Emission color Wavelength of emission peak (nm) External quantum efficiency (%)
Red 620 5.4
Green 523 6.8
Blue 476 2.8
Figure 1 and Table 1 summarize the new EL devices' performance. The quantum efficiencies for G and R exceed 5%. The EL devices can be fabricated by simple methods, such as printing or inkjet method, because the phosphorescent polymers are soluble in common cost organic solvents. This should lower the production of large, high-definition displays.
Along with efforts to improve blue emission capability, we plan to increase the quantum efficiency to 20% for RGB.

* This development was done in cooperation with Showa Denko K.K.





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