July 2019

Researchers at the Tokyo Institute of Technology and Nihon University in Japan have explored a new approach using an exciton confinement effect to optimize highly efficient perovskite LEDs.

The structure of a large perovskite LED, where a layer of zinc oxide was deposited on the a-zinc silicate electron transport layer, providing greater brightness with better power efficiency. Credit: Tokyo Institute of Technology

To achieve an efficient electroluminescent device, the team required a high photoluminescence quantum yield emission layer, efficient electron hole injection and transport layers, and high light out-coupling efficiency. With each new advance in emission layer materials, new functional materials are required to realize a more efficient LED. To accomplish this goal, the authors of the study explored the performance of an amorphous zinc-silica-oxide system layered with perovskite crystals to improve the diode performance.

A team of scientists at Washington University in St. Louis has found what may be a more stable, less toxic semiconductor for solar applications using a novel double perovskite oxide, discovered through data analytics and quantum-mechanical calculations.

An atomic model of KBaTeBiO6 (left), scanning transmission electron micrograph showing the atomic structure of KBaTeBiO6, along with snapshot of the synthesized powder (right). Credit: WUSTL

Rohan Mishra, assistant professor of mechanical engineering & materials science in the McKelvey School of Engineering, led an interdisciplinary, international team that discovered the new semiconductor, made up of potassium, barium, tellurium, bismuth and oxygen (KBaTeBiO₆). The lead-free double perovskite oxide was one of an initial 30,000 potential bismuth-based oxides. Of those 30,000, only about 25 were known compounds.

Researchers at KU Leuven have explained how a promising type of perovskites can be stabilized. The team has developed a process in which the crystals turn black, enabling them to absorb sunlight. This is said to be necessary in order to use them in solar panels.

"Silicon forms a very strong, rigid crystal. If you press on it, it won't change its shape. On the other hand, perovskites are much softer and more malleable," explains Dr. Julian Steele of the KU Leuven Centre for Membrane Separations, Adsorption, Catalysis, and Spectroscopy for Sustainable Solutions (cMACS). "We can stabilize them under various lab conditions, but at room temperature, the black perovskite atoms really want to reshuffle, change structure, and ultimately turn the crystal yellow".

Researchers at the Dalian Institute of Chemical Physics at the Chinese Academy of Science have reported a series of bulk lead-free double perovskites which demonstrate the existence of parity-forbidden transition by photophysical characterization in Cs₂AgInCl₆ bulk crystal. The perovskites break the parity-forbidden transition and show warm white-light emission with broad emission across the entire visible spectrum, with the highest PLQE of 70.3%.

The luminescence property of Cs2AgBi1-xInxCl6 (0

The synthesized nanocrystals and microcrystals revealed that the PLQE decreases with the size decreasing, due to the enhancement of the PL quenching effect, caused by the increase of permanent defects. Furthermore, the Cs₂AgBi_0.125In_0.875Cl₆ bulk crystal possesses excellent stability. Therefore, it's promising as a new highly efficient warm white-light emitting material in LED applications.

Scientists at Germany's Karlsruhe Institute of Technology (KIT) and the Innovation Lab in Heidelberg have developed a highly efficient hole conductor layer made of nickel oxide (NiOx) that can be deposited over a large area and leads to record efficiencies in solar cells with organometallic perovskites.

The team achieved efficiencies of up to 16.1% for completely vacuum-processed perovskite solar cells. With inkjet-printed absorber layers, the scientists achieved an efficiency record of up to 18.5%. "Currently, deposition by rotary coating, for which efficiencies of more than 24% have been achieved, dominates development. However, this can practically not be transferred to large areas" says Tobias Abzieher, PhD student at KIT's Light Technology Institute (LTI).

Scientists at Linköping University (LiU), along with colleagues from China, have shown how to achieve efficient perovskite light-emitting diodes (LEDs). The researchers provide guidelines on fabricating high-quality perovskite light emitters, and consequently high-efficiency perovskite LEDs.

Different metal oxide layers affect the properties of the thin perovskite films. Credit: Charlotte Perhammar

The halide perovskites can be easily prepared by low-cost solution processing from precursor solution comprising metal halides and organic halides. The resulting perovskites reportedly possess excellent optical and electrical properties, making them promising candidates for various kinds of optoelectronic devices, such as solar cells, LEDs and photodetectors.

Penn State researchers have found a new class of 2D perovskite materials with edges that are conductive like metals and cores that are insulating. The researchers said these unique properties may have applications in solar cells and nanoelectronics.

'This observation of the metal-like conductive states at the layer edges of these 2D perovskite materials provides a new way to improve the performance of next-generation optoelectronics and develop innovative nanoelectronics,' said Kai Wang, assistant research professor in materials science and engineering at Penn State and lead author on the study.

Researchers at the Institute of Materials Science in Barcelona (ICMAB-CSIC) and the Helmholtz-Zentrum Berlin für Materialien und Energie (Germany) have used a unique microscopy technique to demonstrate that perovskites are not ferroelectric, as was thought.

The new technique, patented by CSIC in 2017, is the direct piezoelectric force microscopy (DPFM) which, for the first time, is used in lead halide perovskite solar cells.

KAUST researchers have developed a synthetic approach that generates homogeneous and defect-free crystals that have the potential to fast-track the commercialization of perovskite solar cells.

The performance and stability of solar cells depend on the morphology of the perovskite thin films, which act as light-harvesting layers in the devices. A major problem arises from the fact that existing perovskite solar cells usually consist of polycrystalline thin films that are highly disordered and defective, which prevents devices from achieving optimal performance.

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.