New research paves the way to manufacturing efficient, stable, and low-cost quantum dot-based light-emitting diodes (LEDs), which is important for the widespread commercial use of these LEDs in large-area, full-color flat-panel displays or as solid-state lighting sources to replace incandescent and fluorescent lights.

One area of the research focused on improving existing organic LEDs (OLEDs) — multi-layered structures made up of paper-thin organic materials, such as polymer plastics, used to light up display systems. OLEDs use less power and generate crisper, brighter images than those produced by conventional LCDs (liquid crystal displays). Ultra-thin OLED panels are also used as replacements for traditional light bulbs and have potential in 3D imaging.

The other area of the research focused on quantum dots (QDs). These nano-particles are tiny crystals comprised of a combination of sulfur, zinc, selenium, and cadmium atoms. When excited by electricity, QDs emit an array of colored light. The individual colors vary depending on the size of the dots. Tuning or adjusting the colors is achieved by controlling the size of the QDs during the synthetic process.

By integrating both areas of research, a high-performance hybrid LED comprised of both organic and QD-based layers was created. An industrial process known as vacuum deposition is the common way to put the necessary organic molecules in place to carry electricity into the QDs. However, a different manufacturing process called spin-coating is used to create a very thin layer of QDs. Having to use two separate processes slows down production and drives up manufacturing costs.

This obstacle was overcome with a patented device structure that allows for depositing all the particles and molecules needed onto the LED entirely with spin-coating. Such a device structure also yields significantly improved device efficiency and lifetime compared to previously reported QD-based LED devices.

Future research and development will focus on other high through-put, continuous roll-to-roll printing or coating processes that could be used to fabricate large area displays or lighting devices.

This work was done by Jiangeng Xue, Paul Holloway, Lei Qian, and Ying Zheng of the University of Florida.

Lighting Technology Magazine

This article first appeared in the November, 2011 issue of Lighting Technology Magazine.

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