According to EurekAlert !: Organic light-emitting diodes (OLEDs) made from carbonaceous materials are expected to bring a technological revolution in displays in the future, such as the use of them to create ultra-thin, low-power displays that can be folded or wrapped around other structures.
Traditional liquid crystal displays require a fluorescent lamp or a conventional light-emitting diode (LED) to provide a backlight, while OLEDs do not require backlighting. A bigger technological breakthrough is OLED-based laser diodes. Scientists have long dreamed of making organic lasers, but have not been able to achieve this by some of the properties of organic materials. Organic materials, for example, are often not effective at generating the high currents needed for lasers Working under conditions.
Diffusion of Charges in OLED Transport Zone (Thuc-Quyen Nguyen / University of California, Santa Barbara (UCSB))
Recently, recent research by research teams from California and Japan in the United States showed that the use of fine-mode OLEDs to produce bright, low-energy light sources has led scientists to take a crucial step toward organic lasers This week was published as Cover Highlights in the Applied Physics Letters, published by the American Physical Confederation.
Researchers have shown that the key to this result lies in the confinement of charge transport and recombination in the nanometer scale region so that the EL efficiency roll-off extends beyond the sharply reduced current density of OLED efficiency - around two orders of magnitude . The new device architecture achieves this by suppressing heat generation and preventing charge recombination.
"The important effect of suppressing roll-off is to increase the efficiency of the device at high brightness," said Chihaya Adachi of Kyushu University, one of the authors of the paper. "The result is a device that achieves the same high brightness with low power consumption."
"For years, scientists dedicated to organic semiconductors have always dreamed of making electro-organic lasers," said Thuc-Quyen Nguyen, another author of the article, at the University of California, Santa Barbara. . "The laser works under extreme conditions and its current is significantly higher than in normal displays and lighting. At high currents, the energy consumption process is even more pronounced, making lasing difficult."
"We think this study of reducing energy consumption is a step toward implementing organic lasers," Nguyen added.
OLED is how to work
The working principle of OLEDs is based on the interaction of electrons and holes. "To give an example," Adachi said. "You can think of organic semiconductors as a subway filled with passengers, where seats represent molecules and passengers represent high-energy particles, electrons." When people get on the train from one end of the subway They carry additional energy and want to find a place to sit and relax while other passengers get off their seats and get off at the other end of the metro, emptying some of the space or calling "holes" Passengers fill up and when the standing passengers sit down and relax, they release the energy they were carrying in. For the OLED, it emits light energy. "
The fabrication of OLED-based lasers requires current densities of up to several thousand amperes per square centimeter (kA / cm2), but until now, current densities were still limited by thermal effects. "At high current densities, brightness is governed by the annihilation process," Adachi said. "You can imagine that it's like the passengers on the subway collide with each other and lose energy, rather than sitting down and releasing light energy."
In his previous work, Adachi and his collaborators demonstrated the performance of OLEDs at current densities in excess of one ampere per square centimeter (1 kA / cm2), but did not achieve the efficiency required for lasers and bright lighting. In this article, they show that efficiency issues can be solved by using electron beam lithography to make fine-mode OLED structures. The tiny device area supports a charge injection density of 2.8 kA / cm2, while maintaining luminous efficiency 100 times higher than before. "In our device architecture, we effectively restricted the access to the middle of the metro so that passengers could spread to less crowded metros, reducing collisions and annihilation with each other."
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