Perovskite LED - Page 9

A team of researchers from the National Renewable Energy Laboratory (NREL) and the University of Utah has developed a new type of LEDs that utilizes spintronics without needing a magnetic field, magnetic materials or cryogenic temperatures.

'The companies that make LEDs or TV and computer displays don't want to deal with magnetic fields and magnetic materials. It's heavy and expensive to do it,' said Valy Vardeny, distinguished professor of physics and astronomy at the University of Utah. 'Here, chiral molecules are self-assembled into standing arrays, like soldiers, that actively spin polarize the injected electrons, which subsequently lead to circularly polarized light emission. With no magnetic field, expensive ferromagnets and with no need for extremely low temperatures. Those are no-nos for the industry.'

A joint research project by scientists from several China-based universities and laboratories has developed a 2D perovskite material for highly efficient LEDs.

Effects of MeS on phase distribution of perovskite films. The yellow path indicates the exciton energy transfer between nanosheets of different thicknesses. Credit: Nature

LEDs are ubiquitous, but current high-quality LEDs still need to be processed at high temperatures and require elaborate deposition technologies ' which makes their production cost expensive. Scientists have recently realized that metal halide perovskites can be extremely promising candidates for next generation LEDs. These perovskites can be processed into LEDs from solution at room temperature, thus largely reducing their production cost. However, the electro-luminescence performance of perovskites in LEDs still has room for improvements.

Researchers from North Carolina State University and the University of Texas have developed and demonstrated a new approach for designing photonic devices. The new method enabled the team to control the direction and polarization of light from thin-film LEDs, overcoming the widely known obstacles of beam shaping that arise from their Lambertian nature. Such LEDs with directional and polarized light emission could be useful for many photonic applications.

'This is a fundamentally new device architecture for photonic devices,' says Franky So, corresponding author of a paper describing the work and Professor of Materials Science and Engineering at NC State. 'And we've demonstrated that, using our approach, directional and polarized emissions from an organic LED or a perovskite LED without external optical elements can be realized'.

Researchers at Linköping University in Sweden have developed efficient blue LEDs based on halide perovskites. The new LEDs could open the door to cheap and energy-efficient illumination.

Schematic of the PeLED structure and the HAADF cross-sectional device image. Image from Nature Communications

Illumination is responsible for approximately 20 percent of global electricity consumption, a figure that could be reduced significantly if all light sources consisted of light-emitting diodes (LEDs). The blue-white LEDs currently in use, however, need complicated manufacturing methods and are expensive, which makes it more difficult to achieve a global transition. LEDs manufactured from halide perovskites could be a cheaper and more eco-friendly alternative for both illumination and LED-based monitors.

A collaboration between University of Pennsylvania, Seoul National University, the Korea Advanced Institute of Science and Technology, the Ecole Polytechnique Fédérale de Lausanne, the University of Tennessee, the University of Cambridge, the Universitat de Valencia, the Harbin Institute of Technology, and the University of Oxford has yielded an understanding of how a class of electroluminescent perovskite materials can be designed to work more efficiently.

This latest work is based on a past endeavor by Penn theoretical chemist Andrew M. Rappe and Tae-Woo Lee at Seoul National University to develop a theory to help explain experimental results. The material that was studied was formamidinium lead bromide, a type of metal-halide perovskite nanocrystal (PNC). Results collected by the Lee group seemed to indicate that green LEDs made with this material were working more efficiently than expected. 'As soon as I saw their data, I was amazed by the correlation between the structural, optical, and light-efficiency results. Something special had to be going on,' says Rappe.

A research team, led by Professors Byungsoo Bae at KAIST and Taewoo Lee at Seoul National University, has developed a new perovskite light-emitting diode (PeLED) display material.

PeLED is a type of LED that uses perovskite as a light-emitting material. Currently, the production cost is lower than that of organic light emitting diodes (OLEDs) and quantum dot light emitting diodes (QLEDs), and it has the advantage of enabling sophisticated color realization.

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India-based researchers have recently designed a novel synthesis procedure that can produce highly uniform luminescent perovskite nanocrystals with uncommon shapes and surface morphologies.

Their work broadens the range of strategies that can be used for tuning the optical and photonic properties of these materials, which are widely studied for use in solar cells, light-emitting diodes, and electronic displays.

Organic-inorganic hybrid perovskites (OIHPs) have great potential for various applications like solar cells, lighting-emitting diodes (LEDs), field effect transistors (FETs) and photodetectors. Among their most important parameters influencing the power conversion efficiency (PCE) of devices based on perovskite materials is their carrier mobility. However, despite massive progress made by introducing new components into the structure to control the mobility of the carriers, the understanding on the atom level of how the components affect the performance is still lacking.

To address this problem, a research team led by Prof. Luo Yi and Prof. Ye Shuji from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) has synthesized a series of 2D OHIPs films with large organic spacer cations.

Researchers at The University of Cambridge and Zhejiang University recently created highly efficient LEDs by depositing mixed-dimensional perovskites on a thin lithium fluoride interface. The fabrication method they used reportedly resulted in LEDs with impressive external quantum efficiencies, while also enabling the deposition of perovskites on a material that they are typically incompatible with.

Image from Nature Electronics

The researchers have been conducting research into perovskite-based LEDs for a few years now. Back in 2018, they created a near-infrared LED using perovskite-polymer heterostructures that achieved external quantum efficiencies of over 20% and internal quantum efficiencies of almost 100%.