According to a news release from the Department of Energy’s Los Alamos National Laboratory, nanoscale engineering work by the lab’s Nanotechnology and Advanced Spectroscopy team has enhanced the performance of quantum dot light emitting diodes.

According to the lab, quantum dots are nano-sized semiconductor particles whose emission color can be tailored by altering their dimensions. They have near-unity emission quantum yields and narrow emission bands, which generate fantastic color purity. The new work intends to enhance QD-LEDs by utilizing a new generation of engineered quantum dots tuned specifically to have decreased wasteful charge-carrier interactions that contest with the generation 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,” noted Victor Klimov of Los Alamos in a statement.

Incadescent bulbs are quickly being switched out for less wasteful fluorescent light sources. However, the most efficient technique for lighting is direct conversion of electricity into light utilizing electroluminescent devices like LEDs.

Because of spectrally narrow, tailorable emission, and ease of processing, colloidal QDs are appealing materials for LED technologies. In the last ten years, research in QD-LEDs has resulted in major enhancements in their performance, to the stage where it almost satisfies the conditions for commercial products. One challenge remaining is the so-called efficiency roll-off or the drop in efficiency at high currents.

“This ‘droop’ problem complicates achieving practical levels of brightness required especially for lighting applications,” posited Wan Ki Bae, a postdoctoral researcher on the nanotech team.

Through spectroscopic studies on operational QD-LEDs, the researchers have determined that the main reason for the drop in efficiency is an effect called Auger recombination. In this process, as opposed to being emitted as a photon, the energy from recombination of an excited electron and hole is transferred to the leftover charge and subsequently used up as heat.

According to Klimov, this work has also shown two different nano-engineering strategies for getting around the problem in QD-LEDs based on bright quantum dots constructed of cadmium selenide cores overcoated with cadmium sulfide shells.

The first technique decreases the efficiency of Auger recombination itself, which can be completed by including a thin layer of cadmium selenide sulfide ally at the core/shell interface of each quantum dot.

The other technique addresses the issue of charge imbalance by better managing the flow of extra electrons into the dots themselves. This can be done by coating each dot in a thin layer of zinc cadmium sulfide, which selectively hinders electron injection.

“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,” said Jeffrey Pietryga, a chemist in the nanotech team.

The study’s findings are described in greater detail in the journal Nature Communications.