Associate Professor, Department of Photonics Materials Science, Chitose Institute of Science and Technology, and Leader, “Construction of organic semiconductor laser and clarification of device physics”,CREST Project, Japan Science and Technology Agency (JST)
Organic electronics and photonics
Since the 1980's, research on organic semiconductors, both low molecular materials and polymers, has progressed, because of their unique electronic properties different from those of inorganic semiconductors, leading to novel optoelectronic applications.
Our research is now focused on electronic and optical properties of organic semiconductors that are open to novel optoelectronic applications, Organic LED, FET, solar cells and laser diodes. Through material design and synthesis, and new device architectures, we are aiming at realizing new organic devices and establishing device physics of organic semiconductors.
Recently, we clarified detailed exciton decay processes of electrophosphorescence. Photoluminescence of Ir(ppy)3 shows unique emission characteristics due to strong interaction between the central Ir and the ligands. It is independent of temperature, suggesting internal phosphorescence efficiency of 100%. We have also realized injection of very high current density over 1000A/cm2 into organic thin films. While it has been considered hard to inject high current density exceeding 1000A/cm2, we have demonstrated that the injection of high current density is possible for organic thin films, which will open a way to realize organic laser diodes in the near future.
We are also interested in annihilation processes of molecular excitons, Triplet-Triplet, Singlet-Single and Exciton-Charge carrier under high current density.
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Fig. 1 Large Image
OLED (organic light emitting diode) characteristics with Ir(ppy)3 as an emitter. Extremely high electroluminescent efficiency of around 20% was achieved. Due to the photo extraction efficiency of 20%, the internal quantum efficiency approached 100%.
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Fig. 2 Large Image
Current density-voltage characteristics with a phthalocyanine derivative as an organic layer. We realized very high current density over 1000A/cm2, is the highest current density ever reported.
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Relevant papers
- Adachi, C., Thompson, M. E. & Forrest, S. R.
Architectures for efficient electrophosphorescent organic light emitting devices.
IEEE, J Selected Topics Quan. Elec. 8, 372 (2002). - Adachi, C., Baldo, M. A. & Forrest, S. R.
Nearly 100% internal quantum efficiency in an organic light-emitting device.
J. Appl. Phys. 90, 5048 (2001). - Adachi, C., Baldo, M. A., Forrest, S. R. & Thompson, M. E.
High efficiency organic electrophosphorescent diodes with tris(2-phenylpyridine)Iridium doped into electron transport layers.
Appl. Phys. Lett. 77, 904 (2000). - Yokoyama, W., Sasabe, H. & Adachi, C.
Carrier injection and transport of steady-state high current density
exceeding 1000A/cm2 in organic thin films.
Jpn. J. Appl. Phys. 42, L1353 (2003). - Adachi, C. & Tsutsui, T.
“Organic Light Emitting Devices” chapter 3, American Institute of Physics (AIP) (2003).
