Super bright OLED breakthrough progress

Diffusion of charge in OLED transport region

Chinese network technology, by the organic light emitting diode containing carbon material (OLED) is expected to bring a technological revolution display in the future, for example, use them to create a folding or other structure wrapped in thin low-power display.

Traditional liquid crystal displays require the use of fluorescent lights or traditional light-emitting diodes (LED) to provide the background light, while OLED does not require backlighting. A bigger breakthrough of science and technology is a laser diode based on OLED, the scientists have been dreaming of organic lasers, but some characteristics of organic materials and the limit has not yet been achieved, such as organic materials are usually not effective in generating high current required to work under the condition of laser.

Recently, the latest research team from the United States of California and Japan that the fine structure of OLED can produce bright light source, low energy consumption, this discovery enables scientists to organic lasers is a key step, the results of this week was used as the cover highlights published by the American Institute of physics the publication of "Applied Physics Letters".

The researchers showed that the key point of this work is that the charge transport and recombination limits in the nanometer region, so that the light-emitting efficiency roll extend beyond the current density OLED efficiency decreases sharply -- nearly two orders of magnitude. The new device structure achieves this by suppressing the heat and preventing charge recombination.

"The important role of suppressing roll off is to improve the efficiency of the device when it is high," said Adachi, a co-author of the paper, Chihaya of Kyushu University (Kyushu, Japan). "The result is to allow the device to achieve the same high brightness in a low energy state. "

"For years, scientists have been devoted to organic semiconductors has been a dream to produce electric organic laser," according to another author, University of California at Santa Barbara (University of California, Santa Barbara) Thuc-Quyen Nguyen said. "The laser operates under extreme conditions, whose current is significantly higher than that of the conventional display and lighting devices. Under the condition of high current, the process of energy consumption is more remarkable, which makes it difficult to emit laser. "

"We believe that this process to reduce energy consumption, to achieve an organic laser step forward. "Nguyen added.

How OLED works

The working principle of OLED is based on the interaction between electrons and holes. "An example of an image," Adachi says, "is that you can think of organic semiconductors as a line of passengers. The seat represents the molecule, while the passenger represents the energetic particle, the electron. When people get on the bus at the end of the subway, they carry extra energy and want to find a place to sit down and relax. At the same time, some passengers got off the seat from the other side of the subway to get off, vacated some location or called "hole" can be filled by standing passengers. As the passengers sit down and relax, they release the energy they have brought. For OLED, that is, the release of light energy. "

The fabrication of OLED based lasers requires a current density of up to a few thousand amperes per square centimeter (kA/cm2), but until today, the current density is still limited by thermal effects. "In the case of high current density, brightness is controlled by the annihilation process," Adachi said. "As you can imagine, it's like losing a lot of energy to a large number of passengers on the subway, rather than sitting down to release light. "

In previous work, Adachi and his collaborators demonstrated the performance of the OLED when the current density was more than one ampere per square centimeter (1 kA/cm2), but did not meet the efficiency of laser and bright lighting. In this article, they show that the efficiency problem can be solved by the use of electron beam lithography to produce a fine model of the OLED structure. Tiny device area can support 2.8 kA/cm2 charge injection density, while maintaining a higher luminous efficiency than the previous 100 times. "In our device structure, we effectively restrict access to the middle of the subway. In this way, passengers can spread to both ends of the less crowded subway, thereby reducing the collision and annihilation of each other. "

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