2019Advanced TechnologyMaterials Science and Engineering
Ching W. Tang photo

Ching W. Tang

  • / 1947-
  • Chemist
  • IAS Bank of East Asia Professor, The Hong Kong University of Science and Technology, Professor Emeritus, University of Rochester

Pioneering Contributions to the Birth of High-Efficiency Organic Light-Emitting Diodes and Their Applications

Dr. Tang studied light emission processes in electrically-driven organic materials and invented a new device structure in which two carefully-selected materials were stacked, allowing for high-efficiency light emission at low drive voltages. This pioneering work has led to the practical use of organic light-emitting diodes (OLEDs) and their widespread application in displays and lighting.

Profile

Brief Biography

1947
Born in Hong Kong
1970
B.S. in Chemistry, The University of British Columbia
1975
Ph.D. in Physical Chemistry, Cornell University
1975–1981
Research Scientist, Eastman Kodak Company
1981–1990
Senior Research Scientist, Eastman Kodak Company
1990–1998
Research Associate, Eastman Kodak Company
1998–2003
Senior Research Associate, Eastman Kodak Company
2003–2006
Distinguished Research Fellow, Eastman Kodak Company
2006–2017
Doris Johns Cherry Professor, Department of Chemical Engineering, University of Rochester
2013–
IAS Bank of East Asia Professor, The Hong Kong University of Science and Technology
2017–
Professor Emeritus, University of Rochester

Selected Awards and Honors

2001
Carothers Award, Delaware Section of American Chemical Society
2001
Jan Rajchman Prize, Society for Information Display
2004
ACS Award for Team Innovation
2005
Humboldt Research Award
2007
IEEE Daniel E. Noble Award for Emerging Technologies
2011
Wolf Prize in Chemistry
2013
Eduard Rhein Technology Award, The Eduard Rhein Foundation
2014
Nick Holonyak, Jr. Award, The Optical Society
2017
IEEE Jun-ichi Nishizawa Medal
2018
C&C Prize
2018
National Inventors Hall of Fame Inductee
Memberships:
American Physical Society, Hong Kong Academy of Engineering Sciences, National Academy of Engineering, The Hong Kong Academy of Sciences, The Society for Information Display

Achievement

Pioneering Contributions to the Birth of High-Efficiency Organic Light-Emitting Diodes and Their Applications

In the 1950s, a group of organic materials were found to be semi-conductive and their electrical conductivities were found to increase significantly when dopants were added. It was then discovered in the 1960s that some organic materials emit light when a high voltage is applied across them. Though the discovery of this electroluminescence (EL) triggered much research work to develop organic EL devices, the emission efficiency remained low (about 0.1%), and the drive voltage required for EL remained high (several tens of volts); these problems hampered any practical application of EL. However, in 1987, Dr. Ching W. Tang invented a new EL device structure consisting of a stack of two carefully-selected organic molecular layers. He demonstrated that this structure facilitates an efficient flow of electric current that results in efficient light emission from the interface region between the two layers (1), even when the applied voltage is set as low as several volts. This innovation paved the way for the practical application of organic EL devices, also known as organic light emitting diodes (OLEDs).

Dr. Tang’s new device structure consists of an aromatic diamine hole transport layer, in which the holes carry the current, and an 8-hydroxyquinoline aluminum (Alq) electron transport layer, in which the current is carried by the electrons. When a voltage is applied across the device, holes are injected from the anode into the aromatic diamine layer, while electrons are injected from the cathode into the Alq layer. These electrons and holes recombine with each other resulting in light emission with an excellent efficiency in excess of 1%. Dr. Tang set the hole transport layer as thin as 75 nm and the electron transport layer as thin as 60 nm in order to reduce the electrical resistance of the device; it allowed the device to be driven by a voltage of less than 10 V. Moreover, the cathode on the Alq layer was made using a magnesium-silver alloy to ensure both efficient electron injection and chemical stability (1). To increase the light emission efficiency of OLEDs and to control the wavelength of the light they emit, Dr. Tang also invented a more advanced device structure in which a part of the Alq layer was doped with highly fluorescent molecules. By optimizing the position of the doped layer and its dopant concentration, he achieved a five-fold increase in the efficiency and spectral control of the emitted light (2).

These works accelerated the development of new materials and device structures for OLEDs, resulting in substantial improvements in their efficiency and reliability; they have enabled the practical application of OLEDs and led to their widespread use in displays and lighting.

Dr. Tang invented the basic structure of OLEDs to drastically raise their efficiency on the basis of academic studies on organic materials. His pioneering works have enabled the practical use of OLEDs and their applications and constitute a clearly outstanding contribution to the fields of materials science and electronics. Indeed, Dr. Tang is truly worthy of receiving the Kyoto Prize.

 

References

(1) Tang CW & Van Slyke SA (1987) Organic electroluminescent diodes. Applied Physics Letters 51: 913–915.

(2) Tang CW et al. (1989) Electroluminescence of doped organic thin films. Journal of Applied Physics 65: 3610–3616.

Lecture

Abstract of the Lecture

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