My watch list


Platelets instead of spheres make screens more economical

ETH Zürich / Jakub Jagielski

UV light shines on a pane of glass, coated with several layers of two-​dimensional semiconductor nanoplatelets, which emits blue light.

23-Jan-2020: ETH scientists have further developed QLED technology for screens. They have produced light sources that for the first time emit high-​intensity light in only one direction. This reduces scattering losses, which makes the technology extremely energy efficient.

QLED screens have been on the market for a few years now. They are known for their bright, intense colours, which are produced using what is known as quantum dot technology: QLED stands for quantum dot light emitting diode. Researchers at ETH Zurich have now developed a technology that increases the energy efficiency of QLEDs. By minimising the scattering losses of light inside the diodes, a larger proportion of the light generated is emitted to the outside.

Conventional QLEDs consist of a multitude of spherical semiconductor nanocrystals, known as quantum dots. In a screen, when these nanocrystals are excited from behind with UV light, they convert it into coloured light in the visible range. The colour of light each nanocrystal produces depends on its material composition.

However, the light these spherical nanocrystals emit scatters in all directions inside the screen; only about one-​fifth of it makes its way to the outside world and is visible to the observer. To increase the energy efficiency of the technology, scientists have been trying for years to develop nanocrystals that emit light in only one direction (forward, towards the observer) – and a few such light sources already exist. But instead of spherical crystals, these sources are composed of ultra-​thin nanoplatelets that emit light only in one direction: perpendicular to the plane of the platelet.

If these nanoplatelets are arranged next to each other in a layer, they produce a relatively weak light that is not sufficient for screens. To increase the light intensity, scientists are attempting to superimpose several layers of these platelets. The trouble with this approach is that the platelets begin to interact with each other, with the result that the light is again emitted not only in one direction but in all directions.

Stacked and insulated from each other

Chih-​Jen Shih, Professor of Technical Chemistry at ETH Zurich, and his team of researchers have now stacked extremely thin (2.4 nanometres) semiconductor platelets in such a way that they are separated from each other by an even thinner (0.65 nanometre) insulating layer of organic molecules. This layer prevents quantum-​physical interactions, which means that the platelets emit light predominantly in only one direction, even when stacked.

“The more platelets we pile on top of each other, the more intense the light becomes. This lets us influence the light intensity without losing the preferred direction of emission,” says Jakub Jagielski, a doctoral student in Shih’s group and first author of the study published in Nature Communications. That is how the scientists managed to produce a material that for the first time emits high-​intensity light in only one direction.

Very energy-​efficient blue light

Using this process, the researchers have produced light sources for blue, green, yellow and orange light. They say that the red colour component, which is also required for screens, cannot yet be realised with the new technology.

In the case of the newly created blue light, around two-​fifths of the light generated reaches the eye of the observer, compared to only one-​fifth with conventional QLED technology. “This means that our technology requires only half as much energy to generate light of a given intensity,” Professor Shih says. For other colours, however, the efficiency gain achieved so far is smaller, so the scientists are conducting further research with a view to increasing this.

Compared to conventional LEDs, the new technology has another advantage, as the scientists emphasise: the novel stacked QLEDs are very easy to produce in a single step. It is also possible to increase the intensity of conventional LEDs by arranging several light-​emitting layers on top of each other; however, this needs to be done layer by layer, which makes production more complex.

Original publication:
Jagielski J, Solari SF, Jordan L, Scullion D, Blülle B, Li YT, Krumeich F, Chiu YC, Ruhstaller B, Santos EJG, Shih CJ; "Scalable photonic sources using two-​dimensional lead halide perovskite superlattices"; Nature Communications; 2020

Facts, background information, dossiers

  • energy efficiency
  • QLEDs
  • nanoplatelets

More about ETH Zürich

  • News

    Using electrical stimulus to regulate genes

    A team of researchers led by ETH professor Martin Fussenegger has succeeded in using an electric current to directly control gene expression for the first time. Their work provides the basis for medical implants that can be switched on and off using electronic devices outside the body. This ... more

    Lighting the path for cells

    ETH researchers have developed a new method in which they use light to draw patterns of molecules that guide living cells. The approach allows for a closer look at the development of multicellular organisms – and in the future may even play a part in novel therapies.  Highly complex organis ... more

    A new biosensor for the COVID-19 virus

    A team of researchers from Empa, ETH Zurich and Zurich University Hospital has succeeded in developing a novel sensor for detecting the new coronavirus. In future it could be used to measure the concentration of the virus in the environment - for example in places where there are many peopl ... more

  • q&more articles

    Analysis in picoliter volumes

    Reducing time, costs and human resources: many basic as well as applied analytical and diagnostic challenges can be performed on lab-on-a-chip systems. They enable sample quantities to be reduced, work steps to be automated and completed in parallel, and are ideal for combination with highl ... more

    Investment for the Future

    This is a very particular concern and at the same time the demand placed annually on Dr. Irmgard Werner, who, as a lecturer at the ETH Zurich, supports around 65 pharmacy students in the 5th semester practical training in “pharmaceutical analysis”. With joy and enthusiasm for her subject sh ... more

  • Authors

    Prof. Dr. Petra S. Dittrich

    Petra Dittrich is an Associate Professor in the Department of Biosystems Science and Engineering at ETH Zurich (Switzerland). She studied chemistry at Bielefeld University and the University of Salamanca (Spain). After completing her doctoral studies at the Max Planck Institute for Biophysi ... more

    Dr. Felix Kurth

    Felix Kurth studied bioengineering at the Technical University Dortmund (Germany) and at the Royal Institute of Technology in Stockholm (Sweden). During his PhD studies at ETH Zurich (Switzerland), which he completed in 2015, he developed lab-on-a-chip systems and methods for quantifying me ... more

    Lucas Armbrecht

    Lucas Armbrecht studied microsystems technology at the University of Freiburg (Breisgau, Germany). During his master’s, he focused on sensors & actuators and lab-on-a-chip systems. Since June 2015, he is PhD student in the Bioanalytics Group at ETH Zurich (Switzerland). In his doctoral stud ... more

q&more – the networking platform for quality excellence in lab and process

The q&more concept is to increase the visibility of recent research and innovative solutions, and support the exchange of knowledge. In the broad spectrum of subjects covered, the focus is on achieving maximum quality in highly innovative sectors. As a modern knowledge platform, q&more offers market participants one-of-a-kind networking opportunities. Cutting-edge research is presented by authors of international repute. Attractively presented in a high-quality context, and published in German and English, the original articles introduce new concepts and highlight unconventional solution strategies.

> more about q&more

q&more is supported by:


Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE