Researchers demonstrate high light extraction efficiency of perovskite photonic crystals

Researchers at NTU, lead by Assoc. Prof. Wang Hong, recently demonstrated high light extraction efficiency of perovskite photonic crystals fabricated by delicate electron-beam lithography.

Researchers demonstrate high light extraction efficiency of perovskite photonic crystals image

The perovskite photonic crystals exhibit both emission rate inhibition and light energy redistribution simultaneously. They observed 7.9-fold reduction of spontaneous emission rate with a slower decay in perovskite photonic crystals due to photonic bandgap effect (PBG).

Perovskite-based quantum dots - a guest post by Ossila

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.

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

Is Apple developing perovskite-enhanced QD-LED displays?

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.

Apple iPhone XS photo

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.

Perovskite films to enable color-enhanced displays

National University of Singapore researchers have developed a perovskite-based color-enhancement film that may enable richer and more natural colors to next-generation flat-panel electronic displays. The research team is currently working with display companies to commercialize the perovskite color-enhancement film, and hopes to see the technology in consumer electronic products within the next two to three years.

Perovskite film enhanced image quality of displays image

Current commercial display technologies such as OLEDs (organic light-emitting diodes) and QLED (quantum dot light-emitting diodes) can only produce slightly more than 50% of the colors visible to the human eye. This limits the color reproduction that these displays can achieve. A research team from the Department of Chemistry and the Solar Energy Research Institute of Singapore (SERIS) at NUS has developed a color-enhancement film that could allow future display technologies to produce more than 75% of all visible colors. This technology is enabled by using perovskites, which can be tuned by changing its chemical composition to emit light strongly and efficiently in a variety of colors. To make the enhancement films, the research team mixed manometer-sized crystals of the perovskite material with a liquid monomer (precursor of plastics), and triggered a polymerization reaction by illuminating the mixture with white light.

Quantum Solutions demonstrated its perovskite QDs at Displayweek 2018

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.