LED - Page 10

Researchers at the College of Materials Science and Engineering at Nanjing University of Science and Technology in China have developed a technique that greatly enhances perovskite QLEDs' performance and stability compared to single interface processing.

The structure of QLED based on QD films passivated without (b) and with passivation (c). Image from Nature Communications

The team proposed a bilateral passivation strategy through passivating the top and bottom interface of the QD film with organic molecules.

Scientists at UC San Diego have developed a new method to fabricate perovskites as single-crystal thin films, which are more efficient for use in solar cells and optical devices than the current state-of-the-art polycrystalline forms of the material.

Their fabrication method - which uses standard semiconductor fabrication processes - results in flexible single-crystal perovskite films with controlled area, thickness, and composition. These single-crystal films showed fewer defects, greater efficiency, and enhanced stability than their polycrystalline counterparts, which could lead to the use of perovskites in solar cells, LEDs, and photodetectors.

An international research team, led by Stefan Weber from the Max Planck Institute for Polymer Research in Mainz, has found microscopic structures in perovskite crystals that can guide the charge transport in the solar cell.

Clever alignment of these electron highways could make perovskite solar cells more efficient. When solar cells convert sunlight into electricity, the electrons of the material inside the cell absorb the energy of the light. The electrons excited by the sunlight are collected by special contacts on the top and bottom of the cell. However, if the electrons remain in the material for too long, they can lose their energy again. To minimize losses, they should therefore reach the contacts as quickly as possible. Microscopically small structures in the perovskites - so-called ferroelastic twin domains - could be helpful in this respect: They can influence how fast the electrons move.

A joint team of HZB and Humboldt-Universität (HU) Berlin researchers has succeeded in producing functional light-emitting diodes printed from a solution of semiconductor compounds. The research group used a metal halide perovskite for this purpose. This is a material that promises particularly high efficiency in generating light'but on the other hand is difficult to process.

"Until now, it has not been possible to produce these kinds of semiconductor layers with sufficient quality from a liquid solution," says Prof. Emil List-Kratochvil, head of a Joint Research Group at HZB and Humboldt-Universität. For example, LEDs could be printed just from organic semiconductors, but these provide only modest luminosity. "The challenge was how to cause the salt-like precursor that we printed onto the substrate to crystallize quickly and evenly by using some sort of an attractant or catalyst," explains the scientist. The team chose a seed crystal for this purpose: a salt crystal that attaches itself to the substrate and triggers formation of a gridwork for the subsequent perovskite layers.

Helio Display Materials, based in the UK, was spun-off from both Oxford and Cambridge University, to commercialize photoluminescent and electroluminescent perovskite-based materials for the display industry.

Following is an interview with Helio's CEO, Simon B. Jones, discussing the company's technology and business.

A UNIST research team has developed an electrode that can significantly improve the stability of perovskite solar cells. UNIST announced that its research team developed 'flexible and transparent metal electrode-based perovskite solar cells with a graphene interlayer'.

The team suppressed interdiffusion and degradation using a graphene material with high impermeability, the team said. Team leader professor Hyesung Park commented that the research will greatly help not only solar cells but other perovskite-based flexible photoelectric devices such as LEDs and smart sensors.

Some light-emitting diodes (LEDs) created from perovskites emit light over a broad wavelength range. Scientists from the University of Groningen have now shown that in some cases, the explanation of this phenomenon is incorrect. Their new explanation should help scientists to design perovskite LEDs capable of broad-range light emission.

Wide-field photoluminescence micrographs (230_175 μm) show how somePerovskite flakes appear bright green over their entire area (left panel), whilst other flakesexhibit a distinctly red-shifted emission (right panel). Credit: University of Groningen

Low-dimensional (2D or 1D) perovskites emit light in a narrow spectral range and are therefore used to make light-emitting diodes of superior color purity. However, in some cases, researchers have noted a broad emission spectrum at energy levels below the narrow spectrum. This has attracted great interest as it could be used to produce white light LEDs more easily compared to current processes. To design perovskites for specific purposes, however, it is necessary to understand why some perovskites produce broad-spectrum emissions while others emit a narrow spectrum.

Scientists at the University of Cambridge and Okinawa Institute of Science and Technology Graduate University (OIST), have identified the source of "deep traps", a known limitation of perovskite materials caused by a defect, or minor blemish, in the material.

"Deep traps" are areas in the material where energized charge carriers can get stuck and recombine, losing their energy to heat, rather than converting it into useful electricity or light. This recombination process can have a significant impact on the efficiency and stability of solar panels and LEDs.

A team of scientists from the NUST MISIS Laboratory of Advanced Solar Energy has proposed a new approach that uses the two-dimensional inorganic material zirconium trisulfide as the electron transport layer of a perovskite LED. In the future, this may allow the mass production of a new type of light-emitting diodes, as well as solving the problem of LED displays degradation, for example, in smartphones and TVs.

The screens of many modern smartphones and TVs "suffer" from pixel burnout. Due to the presence of an organic component in OLED-type matrices (and their derivatives), pixels begin to degrade when the same icons on the screen are lit for a long time. So far, manufacturers advise users to periodically change the screen interface, rearrange the icons in places and regularly update the screen saver. In fact, the problem could be solved by minimizing the use of organic components in the screen matrix. Perovskite diodes are proposed as a way to make a revolution in designing screens.

University of California, Berkeley, scientists have created a blue light-emitting diode (LED) from halide perovskites, overcoming a major barrier to using these cheap, easy-to-make materials in electronic devices.

In the process, however, the researchers discovered a fundamental property of halide perovskites that may prove a barrier to their widespread use as solar cells and transistors. Alternatively, this unique property may open up a whole new world for perovskites far beyond that of today's standard semiconductors.