Kyushu researchers use perovskites to create micrometer-thick OLEDs

Scientists at Kyushu University in Japan have created micrometer-thick organic light-emitting diodes (OLEDs) by integrating thick layers of hybrid perovskite with thin organic layers. Such devices have the potential to enhance the viewing angles and affordability of high-performance TVs and various other displays.

A test organic light-emitting diode (OLED) incorporating thick layers of hybrid perovskite emits green light imageA test organic light-emitting diode (OLED) incorporating thick layers of hybrid perovskite emits green light. (Image credit: William J. Potscavage Jr., Kyushu University)

OLEDs use layers of organic molecules to efficiently change electricity into light. While these molecules are excellent emitters, they are usually poor conductors of electricity. This is why researchers strive to use extremely thin layers (around 100 nm) to allow electricity to easily reach where emission takes place in the center of the devices.

CSoT demonstrates a 6.6" 384x300 OLED display that uses perovskite quantum dots for color conversion

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.

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)

Perovskites may enable improved, low-cost LEDs

A team of researchers from the University of Macau (UM), Nanjing Tech University, and Nanyang Technological University, Singapore, has announced a significant breakthrough, laying a theoretical foundation for high-efficiency and low-cost perovskite light emitting diode (LED). The research is said to be able to significantly improve the luminous efficiency of perovskite LED and have the potential to advance low-cost, high-efficiency LED displays and LED light sources.

The team discovered that the slow bimolecular recombination that drives 3D lead-halide perovskites' excellent photovoltaic performance is conversely a fundamental limitation for electroluminescence. The team found that the slow bimolecular recombination limitation can be overcome so that high-efficiency electroluminescence can be achieved.

Will perovskite LEDs someday replace LEDs and OLEDs?

Researchers at Pohang University in Korea are reportedly the first to develop a perovskite light emitting diode (PeLED) that could replace organic LED (OLED) and quantum dot LED (QDLED).

Organic/inorganic hybrid perovskite have much higher color-purity at a lower cost compared to organic emitters and inorganic QD emitters. However, LEDs based on perovskite had previously shown a limited luminous efficiency, mainly due to significant exciton (a complex of an electron and hole that can allow light emission when it is radiatively recombined) dissociation in perovskite layers.