Featured Research

from universities, journals, and other organizations

Nanoscale engineering boosts performance of quantum dot light emitting diodes

Date:
October 25, 2013
Source:
DOE/Los Alamos National Laboratory
Summary:
Dramatic advances in the field of quantum dot light emitting diodes could come from recent work. Quantum dots are nano-sized semiconductor particles whose emission color can be tuned by simply changing their dimensions.

The quantum dot device structure shown with a transmission electron microscopy (TEM) image of a cross-section of a real device.
Credit: Image courtesy of DOE/Los Alamos National Laboratory

Dramatic advances in the field of quantum dot light emitting diodes (QD-LEDs) could come from recent work by the Nanotechnology and Advanced Spectroscopy team at Los Alamos National Laboratory.

Quantum dots are nano-sized semiconductor particles whose emission color can be tuned by simply changing their dimensions. They feature near-unity emission quantum yields and narrow emission bands, which result in excellent color purity. The new research aims to improve QD-LEDs by using a new generation of engineered quantum dots tailored specifically to have reduced wasteful charge-carrier interactions that compete with the production of light.

"QD-LEDs can potentially provide many advantages over standard lighting technologies, such as incandescent bulbs, especially in the areas of efficiency, operating lifetime and the color quality of the emitted light," said Victor Klimov of Los Alamos.

Incandescent bulbs, known for converting only 10 percent of electrical energy into light and losing 90 percent of it to heat, are rapidly being replaced worldwide by less wasteful fluorescent light sources. However, the most efficient approach to lighting is direct conversion of electricity into light using electroluminescent devices such as LEDs.

Due to spectrally narrow, tunable emission, and ease of processing, colloidal QDs are attractive materials for LED technologies. In the last decade, vigorous research in QD-LEDs has led to dramatic improvements in their performance, to the point where it nearly meets the requirements for commercial products. One outstanding challenge in the field is the so-called efficiency roll-off (known also as "droop"), that is, the drop in efficiency at high currents.

"This 'droop' problem complicates achieving practical levels of brightness required especially for lighting applications," said Wan Ki Bae, a postdoctoral researcher on the nanotech team.

By conducting spectroscopic studies on operational QD-LEDs, the Los Alamos researchers have established that the main factor responsible for the reduction in efficiency is an effect called Auger recombination. In this process, instead of being emitted as a photon, the energy from recombination of an excited electron and hole is transferred to the excess charge and subsequently dissipated as heat.

A paper, "Controlling the influence of Auger recombination on the performance of quantum-dot light-emitting diodes" is being published Oct. 25 in Nature Communications. In addition, an overview article on the field of quantum-dot light-emitting diodes and specifically the role of Auger effects appeared in the September Materials Research Society Bulletin, Volume 38, Issue 09, also authored by researchers of the Los Alamos nanotech team.

Not only has this work identified the mechanism for efficiency losses in QD-LEDs, Klimov said, but it has also demonstrated two different nano-engineering strategies for circumventing the problem in QD-LEDs based on bright quantum dots made of cadmium selenide cores overcoated with cadmium sulfide shells.

The first approach is to reduce the efficiency of Auger recombination itself, which can be done by incorporating a thin layer of cadmium selenide sulfide alloy at the core/shell interface of each quantum dot.

The other approach attacks the problem of charge imbalance by better controlling the flow of extra electrons into the dots themselves. This can be accomplished by coating each dot in a thin layer of zinc cadmium sulfide, which selectively impedes electron injection. According to Jeffrey Pietryga, a chemist in the nanotech team, "This fine tuning of electron and hole injection currents helps maintain the dots in a charge-neutral state and thus prevents activation of Auger recombination."

These studies were funded by a grant from the U.S. Department of Energy Office of Science.


Story Source:

The above story is based on materials provided by DOE/Los Alamos National Laboratory. Note: Materials may be edited for content and length.


Journal Reference:

  1. Wan Ki Bae, Young-Shin Park, Jaehoon Lim, Donggu Lee, Lazaro A. Padilha, Hunter McDaniel, Istvan Robel, Changhee Lee, Jeffrey M. Pietryga, Victor I. Klimov. The influence of Auger recombination on the performance of quantum-dot light-emitting diodes. Nature Communications, 2013 [link]

Cite This Page:

DOE/Los Alamos National Laboratory. "Nanoscale engineering boosts performance of quantum dot light emitting diodes." ScienceDaily. ScienceDaily, 25 October 2013. <www.sciencedaily.com/releases/2013/10/131025135349.htm>.
DOE/Los Alamos National Laboratory. (2013, October 25). Nanoscale engineering boosts performance of quantum dot light emitting diodes. ScienceDaily. Retrieved October 2, 2014 from www.sciencedaily.com/releases/2013/10/131025135349.htm
DOE/Los Alamos National Laboratory. "Nanoscale engineering boosts performance of quantum dot light emitting diodes." ScienceDaily. www.sciencedaily.com/releases/2013/10/131025135349.htm (accessed October 2, 2014).

Share This



More Matter & Energy News

Thursday, October 2, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Japan Looks To Faster Future As Bullet Train Turns 50

Japan Looks To Faster Future As Bullet Train Turns 50

Newsy (Oct. 1, 2014) Japan's bullet train turns 50 Wednesday. Here's a look at how it's changed over half a century — and the changes it's inspired globally. Video provided by Newsy
Powered by NewsLook.com
US Police Put Body Cameras to the Test

US Police Put Body Cameras to the Test

AFP (Oct. 1, 2014) Police body cameras are gradually being rolled out across the US, with interest surging after the fatal police shooting in August of an unarmed black teenager. Duration: 02:18 Video provided by AFP
Powered by NewsLook.com
Raw: Japan Celebrates 'bullet Train' Anniversary

Raw: Japan Celebrates 'bullet Train' Anniversary

AP (Oct. 1, 2014) A ceremony marking 50 years since Japan launched its Shinkansen bullet train was held on Wednesday in Tokyo. The latest model can travel from Tokyo to Osaka, a distance of 319 miles, in two hours and 25 minutes. (Oct. 1) Video provided by AP
Powered by NewsLook.com
Robotic Hair Restoration

Robotic Hair Restoration

Ivanhoe (Oct. 1, 2014) A new robotic procedure is changing the way we transplant hair. The ARTAS robot leaves no linear scarring and provides more natural results. Video provided by Ivanhoe
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins