Technical / Research - Page 18

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.

Motorola has been granted an interesting patent that aims to solve screen deformation with foldable displays. Motorola says that one of the issues with foldable displays is that they deform in low temperatures.

Motorola suggests using a temperature sensor that detects when the display is deformed, and then the hinge is heated so that the display is automatically corrected. This could be used to create foldable OLEd phones that bend both inward and outwards, and can work with more than one hinge (so that you can fold a display several times).

Researchers from Penn State University have demonstrated 3D OLED lighting devices, inspired by the Japanese Kirigami art of paper cutting the folding.

The researchers started with flexible OLED lighting devices produced on thin plastics, which they then cut and folded to create lighting-emitting 3D structures.

Researchers from the Universitat Autònoma de Barcelona and TU-Dresden have demonstrated that ultra-stable film formation can be used to to improve the performance of OLED devices.

The researchers grew (using evaporation) the organic materials as ultrastable glasses - a growth condition that allows for thermodynamically most stable amorphous solids. Testing four different phosphorescent emitters, the researchers show significant (over 15%) increases of efficiency and operational stability. The researchers also say that these growing conditions are expected to even be more useful for TADF materials.

Researchers from the University of Michigan developed a new method to cost-effectively extra more light out of OLED displays. To achieve that, the researchers used a Sub-Electrode Micro-Lens Array (SEMLA) placed between the bottom transparent ITO electrode and the glass substrate. Testing on green and white PHOLEDs, the researchers say the SEMLA enhanced light output by a factor of 2.8 (green) and 3.1 (white) compared to a similar device without the lens array.

The researcher say that such an array can be fully transparent and has no impact on the sharpness of the display. The hexagonal array of 10 um lenses can be fabricated using conventional photolithography methods which are quite cost effective. Such a micro-lens array does not change the actual OLED production process.

Researchers from Yonsei University managed to use a graphene-like 2D material called Molybdenum Disulfide (MoS₂) to create a transistor that can drive flexible OLED displays.

The researcher created a 6x6 OLED pixel array on a 7 mm plastic substrate that is so bendable (1 mm radius) it can be used as a skin sticker as can be seen in the video above.

Researchers from Samsung Electronics and the Ewha Womans University in Korea collaborated in a new study of the degradation in blue phosphorescence OLED materials. This study demonstrate the importance of controlling exciton-induced electron transfer, and more importantly provides strategies for the design of longer-lasting blue PHOLED materials.

The researchers say that the study reveals the charge-neutral generation of polaron pairs (radical ion pairs) by electron transfer from the dopant to host excitons. According to the study, device lifetime correlates linearly with the rate constant for the annihilation of the radical ion pair.

Researchers from Taiwan's National Tsing Hua University (NTHU) developed a new TADF OLED emitter material that maintains its high efficiency at high luminance. The researchers say that this new material is the world's most efficient TADF emitter at high brightness.

The new material is made from two diboron-based molecules, CzDBA and tBuCzDBA. These donoracceptordonor (DAD) type and rod-like compounds concurrently generate TADF with a photoluminescence quantum yield of ~100% and an 84% horizontal dipole ratio in the thin film. The researchers synthesized a green TADF emitter that achieved a a high external quantum efficiency of about 37.8% with an efficiency roll-off of only 0.3% at 1,000 cd/m².