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New Phosphorescent Polymer for Flexible Displays

January 15, 2002

Showa Denko K.K. (SDK) and Science & Technical Research Laboratories of Japan Broadcasting Corporation have jointly developed a new type of phosphorescent polymer for use in flexible displays that are compact and portable.
Organic electroluminescent devices using this polymer will ensure highly efficient emission of lights in the three primary colors (red, green and blue).

So far, only fluorescent-polymer-based devices, whose theoretical luminous efficiency is 5% maximum, have been used. However, devices that use the newly developed phosphorescent polymer will theoretically be able to attain a maximum luminous efficiency of 20%.

Phosphorescence is usually observed at very low temperature (-196°C of liquid nitrogen) and rarely seen at ordinary temperature. Nevertheless, the newly developed polymer can emit phosphorescence in the red, green and blue lights at ordinary temperature with high efficiency. This has been achieved by incorporating into one polymer the portion for carriage of electrons/holes and the portion for emitting lights. The color of lights can be changed by varying the chemical structure of the light-emitting portion.

The advantages of the newly developed polymer are as follows:

  • 1.Ensures highly efficient emission of red, green and blue lights.
  • 2.Simple application methods (ink jet method, printing method, etc.) can be used to produce large-screen, high-precision displays at a low cost. (While conventional low-molecular-weight materials require expensive vacuum deposition film-forming equipment, this polymer material does not need it.)
  • 3.Leads to production of flexible and stable devices as they are solely based on polymers.

At this moment, the following levels of performances have been achieved (luminance: 100 cd/m2).

  Luminescence wavelength peak Luminous efficiency
Red 620nm 4.6%
Green 523 nm 5.9%
Blue 476 nm 2.7%

Development efforts will continue centering on improvement of the blue color and achievement of the 20% luminous efficiency for the three colors. Furthermore, trial manufacture of full-color panels will be conducted with ink jet process for the purpose of producing high-precision displays.