Technical / Research

Researchers from the Beijing Institute of Technology (BIT) have developed an infrared-to-visible upconversion device (night goggles) that stacks a mercury telluride (HgTe) colloidal quantum dot photodetector directly underneath a dual-emissive-layer OLED. Unlike previous upconverters, which output a single color and encode the infrared signal only as brightness, this device changes both its emitted color and its luminance depending on the wavelength and intensity of the incoming infrared light - effectively giving the wearer full-color infrared vision.

The OLED unit is the key to the color-coding scheme. It uses two separate emissive layers - a red one based on Ir(piq)₃ doped in CBP, and a cyan one based on FIrpic doped in CBP - with a deliberately engineered 0.82 eV hole-injection barrier between the HOMO levels of the two dopants.

Under weak infrared illumination, the small number of photogenerated holes arriving from the quantum dot detector gets trapped in the red dopant and cannot cross into the cyan layer, so the device emits red. Under stronger or shorter-wavelength infrared light, the extra holes saturate the red traps, migrate through the CBP host, overcome the barrier and reach the cyan layer as well - producing a mixed red and cyan emission at higher luminance. The full OLED stack is ITO / HATCN (5 nm) / NPB (30 nm) / TCTA (10 nm) / 8% Ir(piq)3:CBP (15 nm) / 15% FIrpic:CBP (20 nm) / CzPhPy (10 nm) / TPBi (30 nm) / LiF/Al.

Researchers from the Changchun Institute of Applied Chemistry (CIAC), working with collaborators from the University of Science and Technology of China and Central China Normal University, developed a new deep-blue OLED device architecture that reaches an external quantum efficiency (EQE) of 42.0%, a record for this device class.

The OLED device is based on MR-TADF emitters, that combine high efficiency with narrowband, high-purity emission through fast exciton conversion. The researchers say that reaching over 40% EQE in this class has been difficult because most MR-TADF emitters have a low horizontal dipole ratio, which limits how much light can actually be extracted from the device.

Researchers from The University of Toyama have developed the world's first OLED that uses a non-epitaxial crystalline rubrene thin film as the emitter layer. To create this OLED device, the researchers combined an amorphous underlayer with precise annealing processes, 

The researchers produced full OLED devices based on this emitter, and discovered that they exhibit a dramatic increase in current density, up to 1000 times higher than that of conventional amorphous devices. The crystalline OLED also achieved an exceptionally low turn-on voltage of 1.3 V at 1 cd/m². 

Researchers at Nagoya University and Kyushu University have utilized AI and machine learning to design new OLED TADF emitter molecules, focusing on "boron-free" 13-ring frameworks. 

The researchers restricted the molecules to contain only carbon, hydrogen and nitrogen atoms, and generated a virtual library with more than 19,000 molecules. Out of these molecules, 17,000 could be 3D modeled, and then after large-scale screening, 50 promising candidates were selected for higher-level quantum chemical calculations. Finally, the two most promising molecules were selected to be synthesized and tested in actual OLED devices.

Researchers from the University of Chicago, Argonne National Laboratory and the University of Southern Mississippi have shown that a common, inexpensive plastic additive can simultaneously improve both the efficiency and the stretchability of polymer OLED emitter materials - two properties that have traditionally been at odds in stretchable display development.

The team, led by an undergraduate student, Sihong Wang, added small-molecule plasticizers - the same class of additives widely used to make commodity plastics soft and flexible - into polymer TADF OLED emitters. The plasticizer acts as a "molecular spacer" that increases the distance between the polymer chains. This spacing does two things at once: it suppresses triplet-exciton concentration quenching (which raises efficiency) and it improves chain mobility (which raises stretchability).

Researchers at KAIST developed an auxetic-based stretchable display platform, that expand in both width and length when pulled. Such a design could be used to enable a display that stretches in a uniform way at the same ratio in all directions.

The new design uses computational analysis to selectively connect only the necessary points that ensure isotropic expansion throughout the substrate, unlike standard methods that bond the auxetic structure and the stretchable substrate across the entire surface.

Researchers from Korea's ETRI, working together with Gosan Tech and Duksan Neolux, developed a new inkjet printing based process to deposit single-substrate stacked QD-OLED panels. 

Samsung Display, the only company that produces commercial QD-OLED displays, utilizes a process that deposits the OLED emitters and the QD layers on different substrates, which are then bonded together. Producing both the emitters and the QDs on the same substrate will make the process easier (and thus cheaper), and will also enable higher resolutions (as the alignment on the bonding process limits the resolution).  

Researchers from Kyung Hee University published a new study in Advanced Functional Materials that studies the the causses of the short operational lifetime of blue phosphorescent OLEDs. 

The researchers say that intrinsic material toughness (things like bond dissociation energy and molecular rigidity) is not enough to predict how long a device will actually last, because materials with very similar chemical stability can show dramatically different lifetimes. To get to the root cause, the researchers combined two complementary characterization techniques: transient photoluminescence (TrPL), which measures a material's intrinsic exciton behavior under optical excitation, and magneto-electroluminescence (MEL), which probes exciton dynamics under actual electrical operation.

Researchers from Kyoto University, have developed a new molecular design concept for MR-TADF OLED emitters, that spatially expands and amplifies the multiple resonance effect. 

The new molecule, called m-CzB10-Mes has a nano-carbon framework, with a ladder-type structure, and it achieved an emission bandwidth dramatically smaller than those of conventional multiple resonance emitters. Furthermore, the molecule also exhibits excellent TADF performance. 

Researchers from Seoul National University have developed high-performance flexible transparent electrodes, using selective metal deposition. They have successfully implemented these electrodes in a top-emitting OLED device, to demonstrate the effectiveness.

To create these electrodes, the researchers developed a novel metal patterning technology, based on a metal vapor desorption layer (MVDL). MVDL can enable high-resolution metal mesh patterns, down to only a few micrometers (μm), without the need for chemical cleaning or lift-off processes. This helps minimize the damage to the underlying organic layers.