Technical / Research - Page 17

Researchers from Korea's Ulsan National Institute of Science and Technology developed a new perovskite-based LED (PeLEDs) which are flexible enough to fold and are also transparent. It seems as if these LEDs are similar to OLED devices and provide area-lighting and not point-lighting like inorganic LED chips.

Perovskite-based LEDs have been demonstrated before, but this is the first time a transparent and flexible one has been developed, according to the researchers. Perovskite LEDs feature high electron mobility, good color purity, and easy color control.

Researchers from Sweden's Chalmers University have developed a new "double doping" process that basically doubles the efficiency of Polymer OLED emitter materials.

The researchers explain that doping in organic semiconductors operates through what is known as a redox reaction, in which the dopant molecule receives an electron from the semiconductor which increases the electrical conductivity of the semiconductor. The efficiency limit of current doped organic semiconductors has been limited by the fact that each dopant molecule was able to to exchange one electron only. In the new research it was shown how it is possible to move two electrons for every dopant molecule which increases the conductivity of the organic material.

Researchers from the University of Cambridge and Jilin University discovered that radical-based OLEDs feature highly efficient emission - in fact they believe that this discovery could be an elegant solution to the problem of in-efficient OLED emission.

First-generation OLED emitters (fluorescent emitters) have a maximum internal quantum efficiency of 25% - as only a quarter of the electrons are in a singlet-state (that emit light) while 75% of the electrons are in a triplet-state. Current ways to achieve 100% IQE are either based on doping with heavy metals (phosphorescent emission) or either based on delayed fluorescence (TADF).

The Fraunhofer FEP institute, the Holst Center and other partners have developed a 15-meter long OLED lighting panel, the longer OLED device ever (beating their own 2017 record of a 10-meter OLED). This work was done as part of the Lyteus, the EU's €14 million initiative within PI-SCALE.

The partners in this project say that this is the first OLED produced using a new unique roll-to-roll (R2R) process that combines the performance of an evaporated OLED stack with solution processing of auxiliary layers.

Researchers from the University of California Berkley developed a new flexible and lightweight blood oxygen sensor that can map oxygen levels over large area. The sensor uses an array of red and near-infrared OLEDs, together with organic photo-diodes, printed on a flexible substrate.

The research was supported by Cambridge Display Technology, which means that these red and near-infrared printed OLEDs use polymer emitters (PLEDs).

Researchers from Korea's KAIST research institute developed a high-efficiency OLED architecture that uses external scattering medium to achieve an EQE greater than 50%.

Such high EQE was only demonstrated before using complex internal nanostructures or by employing a micro-lens array, but these solutions are complicated to produce and can hinder the OLEDs flexibility and planar structure. The researchers say that their scattering approach maintains the planar geometry , results in flexible OLEDs and can be easily scaled to enable low cost production.

The UK innovation agency (Innovate UK) has launched a new 30-month project called UltraWELD, which aims to improve airtight bonding in OLED lighting for aerospace and defense applications. The project partners will develop photonic-based processes for highly dissimilar material joining.

Current dissimilar materials joining is mainly done using adhesive bonding - a highly flexible and low cost process, but one that cannot provide truly hermetic bonds, which reduces the performance of the panels and can lead to optical damage.

Researchers from the Fraunhofer FEP institute developed a new micro-patterning process using an electron beam to produce OLED microdisplays on silicon substrates. This could enable a new way to produce direct-emission OLED microdisplays, which will be more efficient and bright compared to the current ones that use color filters.

The electron beam patterning is performed after the encapsulation step - the beam goes through the encapsulation layer and can be used to modify the emission of the OLED materials. To create red, green, and blue pixels, an organic layer of the OLED itself is ablated by a thermal electron beam process.

Researchers from Japan's Kyushu University developed a new technology called singlet fission that enables near-infrared OLED materials to surpass the 100% limit for exciton production - or achieve an internal quantum efficiency (IQE) of over 100%. Singlet fission was already used in OPVs, but this is the first time that it was demonstrated with OLEDs.

Achieving over 100% is possible because at 100% IQE all charges form excitons that emit light. The new technique splits the energy from a high-energy excitons into two low level ones. The new OLED emitter materials use molecules in which singlets can transfer half of their energy to neighboring molecules while keeping half of the energy for themselves - each singlet creates two triplets. The emitters emit near-infrared light.

The Fraunhofer FEP announced that it developed a new technology to produce ultra-smooth polymer films. The new technology can be used to produce low-defect density films in a roll-to-roll based process, suitable for a wide range of applications - including encapsulation films, touch layers and as OLED substrates.

This technology was developed as part of the EU-funded OptiPerm project. The Fraunhofer researchers say that this new innovative process does not require any special processing environment and could be used under standard factory conditions.