Quantum Dots Enable Next Generation of LED Lighting Systems

Researchers in Japan fabricate a hybrid inorganic/organic LED that produces white-blue electroluminescence using quantum dots

Photo: Natural Science Center for Basic Research and Development/Hiroshima University
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Quantum dots have gone big time. With Samsung’s first quantum dot televisions shipping last month, production is being ramped up and the decade-and-a-half of promise appears to be coming true.

Now researchers at the University of Hiroshima in Japan have used silicon-based quantum dots for a type of light-emitting diode (LED) that promises to revolutionize lighting systems. The Japanese researchers have fabricated a hybrid inorganic/organic LED that produces white-blue electroluminescence using quantum dots. This white-blue electroluminescence LED promises a next-generation of illumination for flexible lighting and displays.

In research published in the journal Applied Physics Letters, the researchers determined that their quantum dot–based LED could achieve its white-blue luminescence with an applied voltage of 6 volts and reach 78 percent of the effective emission obtained from silicon quantum dots.

To give you sense of how these numbers stack up, about six years ago, the luminescent efficiency of quantum dots used in state-of-the-art electroluminescent LEDs were reduced from more than 90 percent to about 15 percent because the dots had to be packed into an organic film that acted as a transport for the electrons.

The Japanese researchers also report that their LED produced current and optical power densities 280 and 350 times as high as those of previously reported devices. The high current and optical power densities of the quantum dot–based LEDs resulted from optimizing the layered structure in a way that better enabled carrier migration.

The actual physical dimensions of the LED provide an active area of 4 square mm, which is 40 times as large as that of a typical commercial LED. In addition, the thickness of the LED is 0.5 mm.

Perhaps the most appealing aspect of the research is that the new LEDs were entirely fabricated through solution-based processing carried out at room temperature and pressure.

The fabrication process involved taking a glass substrate and then depositing conductive polymer solutions and a colloidal silicon quantum dot solution on top of it.

Ken-ichi Saitow, professor at Hiroshima University and leader of the research added: "QD LED has attracted significant attention as a next-generation LED. Although several breakthroughs will be required for achieving implementation, a QD-based hybrid LED allows us to give so fruitful feature that we cannot imagine."

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