(Nanowerk) - What makes OLEDs so attractive is that they do not require a backlight to function and therefore require less power to operate; also, since they are thinner than comparable LEDs, they can be printed onto almost any substrate.
Nonetheless, exciton quenching and photon loss processes still limit OLED efficiency and brightness. Organic light-emitting transistors (OLETs) are alternative, planar light sources combining, in the same architecture, the switching mechanism of a thin-film transistor and an electroluminescent device.
"OLET is a new light-emission concept, providing planar light sources that can be easily integrated in substrates of different nature – silicon, glass, plastic, paper, etc. – using standard microelectronic techniques," Michele Muccini, a researcher at the Institute of Nanostructured Materials (ISMN) in Bologna, Italy, explains to Nanowerk. "The focus of OLET development is the possibility to enable new display/light source technologies, and exploit a transport geometry to suppress the deleterious photon losses and exciton quenching mechanisms inherent in the OLED architecture."
Reporting their findings in a paper in the May 2, 2010 online edition of Nature Materials ("Organic light-emitting transistors with an efficiency that outperforms the equivalent light-emitting diodes"), the scientists demonstrated the advantages of using an OLET versus an OLED configuration, and enabled OLETs with the highest efficiency reported so far.
"We show that the same organic emitting layer leads to more efficient device emission when it is incorporated in the OLET structure than in the OLED one" says Muccini. "Our devices provide planar micrometer-size light sources that might enable organic photonic applications like integrated on-chip bio-sensing and high resolution display technology with embedded electronics."
The Italian team introduced the concept of using a p-channel/emitter/n-channel tri-layer semiconducting heterostructure in OLETs providing a novel approach to dramatically improve OLET performance. According to Muccini, these devices are more than 100 times more efficient than the equivalent OLED, over 2 times more efficient than the optimized OLED with the same emitting layer, and over ten times more efficient than any other reported OLET.
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