Press Releases
May 25, 2009

Light for the next generation is coming in sight!

Presenters
  • Eiichi Nakamura (Professor,Department of Chemistry, School of Science, The University of Tokyo / Nakamura Functional Carbon Cluster Project, ERATO, Japan Science and Technology Agency)
  • Hayato Tsuji (Associate Professor, Department of Chemistry, School of Science, The University of Tokyo)
  • Yoshiharu Sato (Group Leader, Nakamura Functional Carbon Cluster Project, ERATO, Japan Science and Technology Agency)

Abstract

Figure 1

Figure. Schematic drawing of OLED devices. (Left) heterojunction, (right) homojunctino architecture, and (right-bottom) electroluminescence of dye-doped devices.

Organic light-emitting diodes (OLEDs) are commercialized as displays and lighting. Prof. Eiichi Nakamura and co-workers developed a new ambipolar material, CZBDF, exhibiting well-balanced and high hole and electron mobilities, both greater than 10-3 cm2 V-1 s-1. Using the material, they demonstrated its utility as a host material for efficient homojunction devices that are composed of CZBDF, a minute amount of an emissive dye (1.2-4.4 wt%), a p-dopant (V2O5), and an n-dopant (metallic cesium). The homojunction OLEDs emit red, green, and blue light and performed at a similar level to the state-of-the-art heterojunction architectures, comprising five or six different organic material layers. A green-fluorescent C545T-doped homojunction device showed high EQEmax value of 4.2% at a luminance of 60,000 cd m-2, which is close to the theoretical limit of an OLED fluorescent emission of 5%.

The present proof-of-principle demonstration will stimulate interest in the design of new ambipolar organic materials and of the practical homojunction devices. The development of the new material greatly depends on the progress in precision organic synthesis as well as the well-defined structure and high purity of small molecules. Although the present work employed a vacuum deposition technique, the Lewis acid/zero-valent metal doping strategy can be transferred to a solution process, which is suitable for cost-efficient large-area displays and for white-emitting tandem lighting devices.