Technical / Research - Page 17

US-based OLED material developer Molecular Glasses received a $225,000 SBIR Phase I grant from the National Science Foundation to develop non-crystallizable charge transporting organic materials as OLED functional layers and thermally activated delayed fluorescence (TADF) emitter-layer hosts.

The NSF explains currently used OLED host molecules tend to crystallize and are poor solvents for the emitting molecules leading to decreased light emission efficiency and shortened device lifetime. Molecular Glasses' innovation uses isomeric mixtures of designed molecules that are amorphous and non-crystallizable in all three layers.

Researchers from the University of Southern California (USC) led by Mark E. Thompson (who was the first to report on efficient phosphorescent OLEDs, later commercialized at UDC) developed a new copper-based phosphorescent OLED emitter compound, that could have several advantages to the currently-used iridium compounds.

The researchers say that copper-based emitters could be cheaper (as iridium is an expensive and rare element) - but more importantly could be the key to develop an efficient and long-lasting blue OLED emitter.

Researchers from Italy's ISOF-CNR, University of Naples "Federico II" and Università di Modena e Reggio Emilia have developed new organic n-type FET transistors based on CVD graphene sheets. The researchers say that the new process and materials they used can enable flexible, transparent and short-channel OFETs - which could be used in the future for OLED or OLET displays.

To create the new transistors, the researchers used thermally evaporated thin-films of PDIF-CN2 (a perylene diimide derivative, specifically Flexterra's ActiveInk N1100) as the organic semiconductor for the active channel of the transistor, with the single-layer CVD graphene (grown at Italy's IIT INSTITUTE) as the electrode material

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.