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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 |
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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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