Organic light emitting diodes (OLEDs), which are made from carbon-containing materials, have the potential to revolutionize future display technologies, making low-power displays so thin they'll wrap or fold around other structures, for instance. Conventional LCD displays must be backlit by either fluorescent¹ light bulbs or conventional LEDs whereas OLEDs don't require back lighting². An even greater technological³ breakthrough will be OLED-based laser diodes, and researchers have long dreamed of building organic lasers, but they have been hindered by the organic materials' tendency to operate inefficiently⁴ at the high currents required for lasing.

 

Now a new study from a team of researchers in California and Japan shows that OLEDs made with finely patterned structures can produce bright, low-power light sources, a key step toward making organic lasers. The results are reported in a paper appearing this week on the cover of the journal Applied⁵ Physics Letters, from AIP Publishing.

 

The key finding, the researchers say, is to confine charge transport and recombination to nanoscale areas, which extends electroluminescent efficiency roll off the current density⁶ at which the efficiency of the OLEDs dramatically decreases -- by almost two orders of magnitude. The new device structures do this by suppressing heating and preventing charge recombination.

 

"An important effect of suppressing roll-off is an increase in the efficiency of devices at high brightness," said Chihaya Adachi of Kyushu University, who is a co-author of the paper. "This results in lower power to obtain the same brightness."

 

"For years scientists working in organic semiconductors⁷ have dreamed of making electrically-driven organic lasers," said Thuc-Quyen Nguyen of the University of California, Santa Barbara, another co-author. "Lasers operate in extreme conditions with electric currents that are significantly higher than those used in common displays and lighting. At these high currents, energy loss processes become stronger and make lasing difficult.

 

"We see this work, which reduces some loss processes, as one step on the road toward realizing organic lasers," Nguyen added.

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