A recent study has uncovered promising results that show low-cost quantum dot semiconductors can compete with more expensive technologies.
While quantum dot semiconductors are making their way into televisions and computer displays, there are questions about whether this low-cost technology performs well enough to be used in applications such as solar energy and medical imaging.
Materials scientists and engineers at Stanford University in the US have teamed up with quantum dot pioneer and nanotechnology expert Professor Paul Alivisatos from University of California, Berkeley, to develop a method of measuring how efficiently quantum dots are able to re-emit absorbed light.
Stanford researcher David Hanifi explained in a statement that traditional semiconductors are single crystals, which are grown in a vacuum under special conditions.
“We can make [quantum dots] in large numbers, in a flask, in a lab, and we’ve shown they are as good as the best single crystals,” Hanifi said.
The new measurement technique, described in Science, allowed the researchers to construct quantum dots with light re-emission efficiency more than 99 per cent, while previous techniques could only measure efficiencies up to 99 per cent.
“These materials are so efficient that existing measurements were not capable of quantifying just how good they are. This is a giant leap forward,” Alivisatos said.
Seeing dots
Quantum dots are nanoparticles with properties including the ability to glow when exposed to light. The colour of light they emit depends on the size of the particle. UV light can cause electrons to break free from their quantum dot particles and allow an electrical current to flow.
A drawback in their large-scale application is that a large number of tiny quantum dots are needed to replace single crystal semiconductors, increasing the risk of defects in the manufacture of individual dots that could affect overall performance.
The ability to measure efficiencies at levels over 99 per cent means that each dot can be assessed and tuned to a specific performance efficiency, giving better quality assurance.
To achieve increased measurement efficiency, the researchers also determined how much excess heat the quantum dots were producing, as this indicates inefficient operation. They reported that quantum dot films consistently emitted around 99.6 per cent of absorbed light, with a 0.2 per cent uncertainty.
“It was surprising that a film with many potential defects is as good as the most perfect semiconductor you can make,” said researcher Alberto Salleo.
The researchers are now working to develop even more precise efficiency measurements of up to or over 99.999 percent, which they say could open the door for the development of new quantum dot technologies including biological dyes, luminescent cooling and luminescent solar concentrators.
Bringing manufacturing costs down
Another study at North Carolina State University has devised a new way to manufacture quantum dots in a ‘nanocrystal factory’ (NC Factory), which the researchers believe has the potential to reduce production costs and ensure consistent quality.
This technique, recently published in Advanced Functional Materials, uses three ‘plug-and-play’ modules, and includes a premixing module to mix halide salts and quantum dots in order to improve quality, a velocity sensor to measure reaction times, and a process-monitoring module.
The monitoring system is based on a platform previously developed by the research team.
According to Milad Abolhasani, one of the research authors and assistant professor of chemical and biomolecular engineering, the NC Factory system would reduce the amount of labour needed to keep the production line operating continuously.
“We estimate that the system could cut overall manufacturing costs by at least 50 per cent. It should reduce manufacturing costs of quantum dots for any application and should at least preserve – if not improve – the quality of the quantum dots,” he added.
The researchers hope this cost reduction will make quantum dot technology more feasible for solar energy applications, and are working towards commercialisation of the NC Factory technique.