Tag: LEDs

Optimization of 2D material-based devices

Optimization of 2D material-based devices

How to visualize electric fields in situ to boost the performance of tomorrow’s LEDs

2D materials are excellent candidates for light emission in LED-type components. Furthermore, combining several of these materials with different properties (metal, insulator, semiconductor) theoretically makes it possible to obtain complex components that combine these properties. To function, these components must be connected to electrodes. But where exactly should the electrical voltage be applied? 
To answer this question, a team from the Paris Institute of NanoSciences used the ANTARES beamline to probe operando the distribution of the electric field within a heterostructure composed of two semiconductors.

Two-dimensional (2D) materials, such as transition metal dichalcogenides (TMDs) (e.g., MoS₂, WSe₂, and their derivatives), exhibit strongly enhanced excitonic effects due to the robust Coulomb coupling between electron-hole pairs. This makes them outstanding candidates for light emission in devices such as LEDs. A second key advantage of this materials platform is the ability to assemble these materials without epitaxial constraints. In theory, this allows for the combination of materials with diverse properties—metals, insulators, and semiconductors with tunable bandgaps—to fabricate complex devices. The entire structure is ultimately connected to electrodes, which serve to inject charges or modulate the potential profile. However, a critical challenge remains: the voltage must be applied in the right location! In these structures, the energy landscape is influenced by edge effects, doping, flake thickness, defects, and above all interfaces. In this study, a team from INSP uses the ANTARES beamline to operando probe the electric field distribution within a heterostructure composed of two semiconductors.

In optoelectronic devices, electrodes are used to inject the current/energy necessary for device operation. In the context of LEDs, applying a bias is essential to inject holes into the valence band while electrons are resonantly injected into the conduction band. When these energy conservation rules are fulfilled, charges can be injected into the optically active semiconductor, enabling light emission. However, the turn-on voltage for an LED can be significantly larger than the material’s bandgap if an electric field is also applied to the intermediate material between the electrode and the optically active layer. This results in power efficiency losses, which must be mitigated. Therefore, the localization of the electric field is critical, and tools to measure the field distribution operando are essential.

Read more on the SOLEIL website

Developing unbreakable screens

Developing unbreakable screens

Cracked phone screens could become a thing of the past thanks to breakthrough research by a global team of scientists

Diamond’s electron Physical Science Imaging Centre (ePSIC) was used in a study that has unlocked the technology to produce next-generation composite glass for lighting LEDs as well as smartphone, television and computer screens. 

The research was recently published in the journal Science and was carried out by an international collaboration involving scientists and engineers from the University of Queensland, University of Leeds, University of Cambridge and Université Paris-Saclay. The findings will enable the manufacture of glass screens that are not only unbreakable but also deliver crystal clear image quality.  

Better LEDs 

The study is focused on nanocrystal materials known as lead halide perovskites, which are promising candidates for light emitting diodes. A powerful electron microscope at ePSIC allowed the team to study the structure of this material. The breakthrough has been the ability to stabilise a particular crystal at room temperature.   

Read more on the Diamond website

Image: Examples of the fabricated glass composite shown under a UV light (black light) to reveal the emission of bright and pure colours. The colour of light emitted from each sample is determined by the chemistry and the size of the nanocrystals embedded in a metal-organic framework glass.

Credit: University of Queensland.

Towards better LED lighting

Towards better LED lighting

Designing energy efficient, high output, perfectly tinted LEDs

SASKATOON – Scientists have combined experimental data gathered at the Canadian Light Source at the University of Saskatchewan and theoretical data to build deep insight into two types of light emitting crystals for next-generation LEDs.

“When we have means of creating more efficient lighting, this has a huge environmental impact,” says Alexander Moewes, Canada Research Chair in Materials Science with Synchrotron Radiation at the University of Saskatchewan, who cites that lighting accounts for 15-20% of global electricity consumption, and therefore for roughly 5% of worldwide greenhouse gas emissions.

Read more on the CLS website

Image: Tristan de Boer,  Patrick Braun, Ruhul Amin, Alexander Moewes and Amir Qamar outside the Physics building at USask

Creating the best TV screen yet

Creating the best TV screen yet

Breakthrough in blue quantum dot technology

There are many things quantum dots could do, but the most obvious place they could change our lives is to make the colours on our TVs and screens more pristine. Research using the Canadian Light Source (CLS) at the University of Saskatchewan is helping to bring this technology closer to our living rooms.

Quantum dots are nanocrystals that glow, a property that scientists have been working with to develop next-generation LEDs. When a quantum dot glows, it creates very pure light in a precise wavelength of red, blue or green. Conventional LEDs, found in our TV screens today, produce white light that is filtered to achieve desired colours, a process that leads to less bright and muddier colours.

Until now, blue-glowing quantum dots, which are crucial for creating a full range of colour, have proved particularly challenging for researchers to develop. However, University of Toronto (U of T) researcher Dr. Yitong Dong and collaborators have made a huge leap in blue quantum dot fluorescence, results they recently published in Nature Nanotechnology.

Read more on the Canadian Light Source website

Image: The blue quantum dot solution glows in a vial in a laboratory.

Atomic Flaws Create Surprising, High-Efficiency UV LED Materials

Atomic Flaws Create Surprising, High-Efficiency UV LED Materials

Subtle surface defects increase UV light emission in greener, more cost-effective LED and catalyst materials

Light-emitting diodes (LEDs) traditionally demand atomic perfection to optimize efficiency. On the nanoscale, where structures span just billionths of a meter, defects should be avoided at all costs—until now.

A team of scientists from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Stony Brook University has discovered that subtle imperfections can dramatically increase the efficiency and ultraviolet (UV) light output of certain LED materials.

“The results are surprising and completely counterintuitive,” said Brookhaven Lab scientist Mingzhao Liu, the senior author on the study. “These almost imperceptible flaws, which turned out to be missing oxygen in the surface of zinc oxide nanowires, actually enhance performance. This revelation may inspire new nanomaterial designs far beyond LEDs that would otherwise have been reflexively dismissed.”

>Read more on the NSLS-II website

Image: The research team, front to back and left to right: Danhua Yan, Mingzhao Liu, Klaus Attenkoffer, Jiajie Cen, Dario Stacciola, Wenrui Zhang, Jerzy Sadowski, Eli Stavitski.