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In new quantum-dot LED design, researchers turn troublesome molecules to their advantage
Date:11/15/2011

Cambridge, Mass. November 15, 2011 By nestling quantum dots in an insulating egg-crate structure, researchers at the Harvard School of Engineering and Applied Sciences (SEAS) have demonstrated a robust new architecture for quantum-dot light-emitting devices (QD-LEDs).

Quantum dots are very tiny crystals that glow with bright, rich colors when stimulated by an electric current. QD-LEDs are expected to find applications in television and computer screens, general light sources, and lasers.

Previous work in the field had been complicated by organic molecules called ligands that dangle from the surface of the quantum dots. The ligands play an essential role in quantum dot formation, but they can cause functional problems later on.

Thanks to an inventive change in technique devised by the Harvard team, the once-troublesome ligands can now be used to build a more versatile QD-LED structure. The new single-layer design, described in the journal Advanced Materials, can withstand the use of chemical treatments to optimize the device's performance for diverse applications.

"With quantum dots, the chemical environment that's optimal for growth is usually not the environment that's optimal for function," says co-principal investigator Venkatesh Narayanamurti, Benjamin Peirce Professor of Technology and Public Policy at SEAS.

The quantum dots, each only 6 nanometers in diameter, are grown in a solution that glows strikingly under a black light.

The solution of quantum dots can be deposited onto the surface of the electrodes using a range of techniques, but according to lead author Edward Likovich (A.B. '06, S.M. '08, Ph.D. '11), who conducted the research as a doctoral candidate in applied physics at SEAS, "That's when it gets complicated."

"The core of the dots is a perfect lattice of semiconductor material, but on the exterior it's a lot messier," he says. "The dots are coated with ligands, long organic chai
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Contact: Caroline Perry
cperry@seas.harvard.edu
617-496-1351
Harvard University
Source:Eurekalert

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