Liquid-OLED design could boost lifetime for OLED displays
August 27, 2009
Researchers from the Center for Future Chemistry at Kyushu University in Fukuoka, Japan, have been exploring a new kind of organic light-emitting diodes that use a generated liquid to transfer electrical charge, addressing problems such as flexibility and quick degradation in standard OLED technology.
Limitations of standard OLED technology
The vast majority of today's consumer electronics monitors are based on LCD (liquid crystal) technology. While these constitute a reliable and durable solution, scientists are constantly searching for advances that would bring immediate benefits to mobile technology, where displays consume a good portion of a device's batteries.
Organic LEDs, or OLEDs, seems to be the direction the display industry is heading at the moment. Using a polymer that allows organic compounds to be deposited with a simple and inexpensive printing process, these devices yield numerous advantages over LCD displays, particularly in terms of reduced power consumption, as they don't require a backlight to function. Other advantages that derive directly from the absence of a backlight include their thinness and a wider viewing angle.
However, today's OLEDs have the disadvantage of being significantly less durable than current display technology, with a lifetime that depends on the specifics and usage modality, but typically ranges between 25 and 50 percent of a standard LCD display.
Beyond OLEDs: liquid-OLEDs
Researchers Denghui Xu and Chihaya Adachi have recently tackled this issue by designing a peculiar kind of OLED that incorporates a liquid-emitting layer. It promises strong advantages in terms of durability, as well as allowing for flexible displays, an interesting step forward for display technology as well as other organic electronics applications.
The team used ethylhexyl carbazole (EHCz) as the liquid semiconductor, exploiting its good electrical conductivity, in combination with solid rubrene, a compound already used in OLED technology and known for its high photoluminescence efficiency. By combining the two and placing them between two electrodes enclosed in glass, the researchers could observe electroluminescence with the naked eye.
By using a liquid as the semiconducting layer, typical problems of bendable displays such as wrinkling and delamination are instantly removed from the picture. What's more, the researchers suggested that the liquid semiconductors in the emitting layer could be periodically refilled, generating a fresh supply of semiconductors that would dramatically slow down the device degradation process, therefore boosting its lifetime.
There is, however, an issue still to be tackled: even though this technology looks promising, the problem of the relatively low electroluminescence efficiency that comes from the ethylhexyl carbazole-rubrene combination still needs to be addressed. The scientists, however, seem confident that they will soon be able to make things better by optimizing the device parameters and organic semiconductors.
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