The small area flat panel display industry in Hong Kong, which represents about 20 per cent of the world market, could soon be getting a range of new frontier technology as a result of research at CityU.
As well as developing new technologies behind organic light emitting diode (OLED) displays, the university is looking at basic research involving organic electronluminescence issues such as new materials, and new device structures, interfaces, machanisms, efficiency and stability.
OLED displays have a range of performance advantages over liquid crystal displays (LCDs), including wider viewing angles, higher contrast, faster response time, flexible panels, and potentially lower manufacturing costs. One research project, completed in February, looked at good and undesirable properties in the construction of OLEDs with the objective of increasing quality and life-time.
"OLEDs will potentially replace LCD display panel technology in many consumer electronic products, from cellular phones and PDAs, to watches and computers," said Principal Investigator Prof Shuit-tong Lee from CityU's Department of Physics and Materials Science.
The research came up with four significant discoveries: l That, because of the small interaction between metal and organic molecules, energy level alignment at the interfaces does not follow the common model of vacuum level alignment.
That the presence of the metallic element indium in organic layers increases drive voltage and reduces luminescence efficiency.
That, contrary to common belief, devices prepared at high temperature to induce crystallization of organic layers show considerable improvement in luminescent efficiency, brightness, as well as storage stability in air, compared to devices prepared at room temperature.
That water is the main cause of chemical reactions when thin films of organic semiconductors are exposed to normal ambient conditions.
Prof Lee said: "The results improve our understanding of the fundamental physics involved in OLED which can lead to better design, enhanced performance, as well as good operational and storage stability." Development in OLED technology is forecast to increase the industry's worth from US$66 million this year to US$714 million in 2005, he added. CityU has established itself as a pioneer in the development of OLED technology in Hong Kong and Mainland China.
To sustain its status in the future, the university has added weight to broadening its research from device optimisation to other areas such as the search for new materials. An on-going project due for completion next February, is looking at a number of important issues including new materials, material / interface characteristics, and the mechanisms of electroluminescence efficiency and stability. Part of the research work has focused on the shortcomings of a typical flourescent molecule, perylene.
At low concentrations perylene has a high flourescent yield. However, with higher concentrations, its flourescent yield decreases. By adding chemical groups to convert perylene into tetra-tert-butylperylene (TBPe), researchers believe they have found a solution to the drop-off in flourescent yield.
The improvement makes TBPe a better organic material for OLED applications. Prof Lee said: "What this project will deliver will be a range of sustainable frontier technology for the flat panel display industry in Hong Kong, and possibly a new direction towards high performance electronic devices."