Quantum Dots - Page 7

China-based display maker China Star (CSoT, a subsidiary of TCL) demonstrated a 6.6-inch 384x300 OLED display that uses perovskite quantum dots as a color conversion film.

CSoT is using blue OLED emitter materials, and a perovskite layer to up-convert the color to green (this is a monochrome prototype - evidently a very early prototype). CSoT brands its perovskite-OLEDs as PE-OLED and we believe this is the first time a perovskite-enhanced display has been publicly demonstrated.

A Taiwan-based research team has developed spray synthesis technology for producing perovskite quantum dots (PQDs). The technology reportedly features a photoluminescence quantum yield rate of nearly 100% and high color purity and stability of PQDs, according to Ministry of Science and Technology (MOST), which sponsors the R&D project.

Using spray synthesis technology, nanometer-sized perovskite crystals are separated from perovskite precursors in solvent and then the crystals are centrifuged to extract PQDs of same sizes, said Lin Hao-wu, which leads the team from the Department of Material Science and Engineering, National Tsing Hua University (NTHU).

Researchers from the Graphene Flagship have managed to increase the stability of perovskite solar cells (PSCs) using hybrids of graphene and molybdenum disulphide quantum dots.

The team used molybdenum disulphide quantum dot/graphene hybrids to address PSCs' instability issue. The collaboration between research institutions and industrial partners enabled by Graphene Flagship, yielded an ink based on graphene and related materials (GRMs). Layering this over the PSCs caused them to drastically increase in stability.

Researchers from North Carolina State University have developed a microfluidic system for synthesizing perovskite quantum dots across the entire spectrum of visible light. The system is said to drastically reduce manufacturing costs, can be tuned on demand to any color and allows for real-time process monitoring to ensure quality control.

Quantum dots (QDs) are promising materials for applications ranging from biological sensing and imaging to LED displays and solar energy harvesting. The new system can be used to continuously manufacture high-quality QDs for use in these applications. "We call this system the Nanocrystal (NC) Factory, and it builds on the NanoRobo microfluidic platform that we unveiled in 2017," says Milad Abolhasani, an assistant professor of chemical and biomolecular engineering at NC State and corresponding author of the study.

Researchers at MIT, ETH Zurich and Empa have made major steps toward finding a photon source with constant, predictable, and steady characteristics. In the quest to develop practical computing and communications devices based on the principles of quantum physics, such a source of individual particles of light is extremely desirable. The study involves using perovskites to make light-emitting quantum dots.

Scanning Transmission Electron Microscope image (STEM) of single perovskite quantum dots

The ability to produce individual photons with precisely known and persistent properties, including a wavelength, or color, that does not fluctuate at all, could be useful for many kinds of proposed quantum devices. Since each photon would be indistinguishable from the others in terms of its quantum-mechanical properties, it could be possible, for example, to delay one of them and then get the pair to interact with each other, in a phenomenon called interference.

What are Quantum Dots?

Quantum dots (QDs) are semiconducting nanocrystals that are very small ' only a few nanometres in size. In display technologies, the most common types of QDs used are composed of a metal chalcogenide core. These QDs have the chemical formula XY ' where X is a metal and Y is sulfur, tellurium or selenium (e.g. CdTe, CdSe, ZnS) ' which is encased with the shell of a second semiconductor (e.g. CdSe/CdS). Their tiny dimensions mean that charge carriers are confined in close proximity, which gives QDs optical and electronic properties that are substantially different from those of large semiconductor crystals.

QLEDs vs OLEDs

In particular, QDs have enhanced light absorption and emission, making them particularly suitable for display technologies. Metal chalcogenide quantum dots (MCQDs) have already made it into commercial products ' most notably, in Samsung's QLED television range. Here, a blue LED backlight excites a layer of quantum dots on an LCD panel, causing them to emit light. The color of light emitted by the quantum dots depends on their size ' with small dots emitting blue light, and progressively larger dots emitting green, yellow, orange, and red light.

Left: Core-shell quantum dot structure. Right: The size of the dot defines the color of light that the dot emits. (Source: Ossila.com)

Quantum Dots are used today in the display industry to enhance the quality and efficiency of LCD-based displays, most notably in TVs (one example is Samsung's premium QLED TV range). While these are still LCD displays enhanced by QDs, quantum dots also have the larger potential to create truly emissive displays (QD-LED) which could compete with OLEDs and even surpass them in quality, efficiency and ease of production.

Several companies (including Samsung, BOE, LG, CSoT and others) are indeed developing QD-LED displays (Samsung, interestingly, is preparing to kick-start hybrid QD-OLED TV pilot production next year). Apple is not left behind, and the company is already known to be looking into QD-LED technologies.

Quantum Materials Corp., manufacturer of Cadmium-free quantum dots, recently announced it has developed a continuous flow manufacturing process to produce stable, low cost, high purity perovskite quantum dots (PQDs). Quantum Materials Corp has reportedly developed a high volume production process that produces extremely high purity PQDs with significantly improved stability.

PQDs have many unique properties that make them an ideal material for utilization in applications such as solar cells and displays. PQD-enhanced solar cells have demonstrated impressive conversion efficiencies, and as a phosphor replacement in flat panel displays, PQDs have the potential to provide industry excellent color gamut picture qualities due to their extremely narrow emission wavelength profile.

Saudi Arabia-based Quantum Solutions demonstrated its perovskite quantum dots (with a focus on its green-colored ones) at SID Displayweek 2018, in addition to its Lead-Sulfide (PbS) QDs.

Quantum Solutions says it uses a flow reactor to create uniform and high-quality QDs at high yields and minimal waste. The company also develops encapsulation technology to protect the perovskite QDs. Their current materials have a lifetime of around 8,000 hours.

China-based QD developer Zhijing Nanotech demonstrated its perovskite-QD film (PQDF) at Displayweek 2018. The company showcased a 55" LCD TV that uses the film to convert the blue LED color to a white background.

Zhijing Nanotech says that its low-cost PQDF can be used to achieve a high 110%+ NTSC color gamut and a high efficiency.