LED - Page 11

Researchers from the University of California San Diego, King Abdullah University of Science and Technology and the Air Force Research Laboratory have developed a technique that could enable the fabrication of longer-lasting and more efficient perovskite solar cells, photodetectors, and LEDs.

Strain-engineered, single crystal thin film of perovskite grown on a series of substrates with varying compositions and lattice sizes. Image Credit: David Baillot/UC San Diego Jacobs School of Engineering.

A major obstacle is the tendency of one of the best-performing perovskite crystals, α-formamidinium lead iodide (HC(NH₂)₂PbI₃, known as α-FAPbI₃), to assume a hexagonal structure at room temperature, in which photovoltaic devices are required to operate. This hexagonal structure cannot respond to most of the frequencies of light in solar radiation, and is hence not useful for solar applications as it could be. The team therefore set out to stabilize the structure of α-FAPbI3, using a simple but useful approach known as strain engineering, which has been used to tune the electronic properties of semiconductors.

A research team led by Tan Zhi Kuang from the Department of Chemistry and the Solar Energy Research Institute of Singapore (SERIS) has developed perovskite-based high-efficiency, near-infrared LEDs that can cover an area of 900 mm² using low-cost solution-processing methods.

Infrared LEDs are generally small point sources, and according to the institute this limits their efficacy if illumination is required in larger areas when in close proximity, such as those found on wearable devices.

Researchers at the National University of Singapore (NUS) have developed highly efficient, large-area and flexible perovskite-based near-infrared LEDs for new wearable device technologies.

The team, led by Tan Zhi Kuang from the Department of Chemistry and the Solar Energy Research Institute of Singapore (SERIS), has developed high-efficiency near-infrared LEDs which can cover an area of 900 mm² using low-cost solution-processing methods. This is several orders of magnitude larger than the sizes achieved in previous reports, and opens up a range of new applications.

Scientists at Duke University have used their electronic structure based materials modeling software on a supercomputer to help demonstrate the advantages of incorporating organic building blocks into hybrid perovskites.

The models showed that the new materials feature improved stability and safety while exhibiting a 'quantum well' behavior that can improve the performance of optoelectronic devices such as solar cells, LEDs and optical computers, making the hybrid perovskites more attractive for use in a broad range of applications.

Scientists at the University of Cambridge studying perovskite materials for use in solar cells and flexible LEDs have discovered that they can be more efficient when their chemical compositions are less ordered, simplifying production processes and lowering cost.

The surprising findings are the result of a collaborative project, led by Dr. Felix Deschler and Dr. Sam Stranks.

Researchers at Tohoku University in Japan have found a new way to successfully detect the efficiency of crystal semiconductors. For the first time, the team used a specific kind of photoluminescence spectroscopy, a way to detect light, to characterize the semiconductors. The emitted light energy was used as an indicator of the crystal's quality. This method will potentially yield more efficient light-emitting diodes (LEDs), solar cells and several other advances in electronics.

Schematic of the ARPL measurement technique

"For further development of perovskite-based devices, it is essential to quantitatively evaluate the absolute efficiency in high-quality perovskite crystals without assuming any predefined physical model is of particular importance," said corresponding author Kazunobu Kojima, Associate Professor at Tohoku University, Japan. "Our method is new and unique because previous methods have relied on efficiency estimation by model-dependent analyses of photoluminescence."

Researchers from Zhejiang University, the Beijing Institute of Technology and Nanjing Tech University in China, Argonne National Laboratory in the U.S, University of Cambridge in the UK have combined perovskite nanoparticles with 2D perovskites to double the efficiency of blue LEDs.

Bromide perovskite films consisting of nanoparticles embedded within 2-D perovskite layers produce blue LEDs with a record-high efficiency of 9.5%

While the device only glows for a few minutes, the work is still considered 'a big step toward the development of high-performance blue perovskite emitters' says Jianjun Tian of the University of Science and Technology in Beijing, who was not involved in the work. 'The efficiency of these blue perovskite LEDs is already higher than that of the commercially available blue organic LEDs.'

Researchers at the Tokyo Institute of Technology (Tokyo Tech) have designed a new strategy to make efficient perovskite-based LEDs with improved brightness by leveraging the quantum confinement effect.

(A) Photoluminescence and (B) electroluminsecence in low-dimensional and 3D perovskite-based devices

Devices that emit light when an electric current is applied, are referred to as electroluminescent devices, which have become orders of magnitude more efficient than the traditional incandescent light bulb. Light-emitting diodes (LEDs) make for the most notable and prevalent category of these devices. Many additional types of LEDs also exist.

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.

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.