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Organic light-emitting diode (OLED) microdisplays have attracted considerable attention owing to their low power consumption, rapid response, high contrast ratio, and self-luminescence. To expand the use of OLED microdisplays, high luminance and vivid color are required. Herein, we developed a high-luminance, low-voltage, three-wavelength, top-emitting white OLED (WOLED) using a silicon substrate for complementary metal–oxide–semiconductor-based, full-color microdisplay applications. Optimal thickness of the emitting layer and thickness and position of the interlayer were determined to improve device performance. The device exhibited luminance of ∼4,200 cd/m2 at 3.3 V, and the maximum luminance reached 170,000 cd/m2 at 11.4 V. In addition, red, green, and blue color filters were deposited onto the WOLED after the thin-film encapsulation process to verify feasibility of the device for full-color microdisplay applications. The color gamut of the developed WOLED with color filters was 136% compared to sRGB. The maximum luminance and color gamut of the developed device is among the highest values obtained to date for OLED microdisplays.

Microdisplays based on organic light‐emitting diodes (OLEDs) have a small form factor, and this can be a great advantage when applied to augmented reality and virtual reality devices. In addition, a high‐resolution microdisplay of 3000 ppi or more can be achieved when applying a white OLED structure and a color filter. However, low luminance is the weakness of an OLED‐based microdisplay as compared with other microdisplay technologies. By applying a tandem structure consisting of two separate emission layers, the efficiency of the OLED device is increased, and higher luminance can be achieved. The efficiency and white spectrum of the OLED device are affected by the position of the emitting layer in the tandem structure and calculated via optical simulation. Each white OLED device with optimized efficiency is fabricated according to the position of the emitting layer, and red, green, and blue spectrum and efficiency are confirmed after passing through color filters. The optimized white OLED device with color filters reaches 97.8% of the National Television Standards Committee standard.

Precise transfer and attachment of a single nanowire to a target substrate is an interesting technique in surface engineering. The spacing, which restrains the attachment of a nanowire to a substrate, and the bending strain that occurs when the nanowire detaches from the elastomeric donor are important design parameters. In this regard, in this study, all-atom molecular dynamics (MD) simulations were conducted to analyse the mechanical behaviour of a penta-twinned silver nanowire (AgNW) placed on a polydimethylsiloxane (PDMS) donor substrate to elucidate the relevant transfer process. The bow deformation of the AgNW at the delamination front of PDMS was characterized as a function of its diameter and aspect ratio. The mechanisms of dislocation slip and propagation as well as the internal stress distribution of the AgNW were then examined. The results showed that twin boundary formation during the bow deformation is a key factor affecting the strain hardening of the AgNW and leading to complete plastic strain recovery after the removal of the PDMS substrate. Furthermore, the process was demonstrated experimentally by a localized bonding and transfer of AgNWs by continuous-wave laser irradiation. Based on the computational and experimental findings, an empirical model considering the shape parameters of AgNWs that can ensure a successful transfer process was established, which is essential for high-performance AgNW electrode design.

We investigated the dependence of the device characteristics of inverted red colloidal quantum dot light-emitting diodes on the hole transport layer. Three different hole transport materials, 4,4′-bis(carbazole-9-yl)biphenyl, 4,4,′4″-tri(N-carbazolyl)triphenylamine, N, N′-bis(naphthalen-1-yl)-N, N′-bis(phynyl)-2,2′-dimethylbenzidine, and six different hole transport layer structures were used for comparing the devices’ performances. The turn-on voltage of the devices was dominated by the energy level difference between the lowest unoccupied molecular orbital of the hole-injection layer (molybdenum trioxide) and the highest occupied molecular orbital of the adjacent hole transport material. The hole mobility as well as the energy level difference between the valence band of the quantum dot and the highest occupied molecular orbital of the adjacent hole transport material was significant factors for high luminance and efficiency. Among the considered devices with six different hole transport layer structures, the device with a single 4,4′-bis(carbazole-9-yl)biphenyl layer as a hole transport layer exhibited the best performance, with a peak efficiency of 5.56% at ~10 mA/cm2. All of the devices exhibited nearly the same main emission peak at ~641 nm and a narrow full-width-half-maximum of ~34 nm, and their International Commission on Illumination 1931 color coordinates were very deep red, nearly the same as the BT.2020 red color coordinate of (0.708, 0.292).

Organic light-emitting diode (OLED) microdisplays have attracted much attention as displays for small form factor augmented reality (AR) devices. To realize glass-like thin and wide field of view (FoV) AR devices, we designed a display module with a high aspect ratio microdisplay and a thin optical component. For the high aspect ratio microdisplay, we developed the color OLED microdisplay with a 32:9 aspect ratio and a 0.8-inch diagonal ∼2,490-ppi CMOS backplane. To express color and reduce optical crosstalk, we fabricated the color filter (C/F) patterning directly on the white OLED. We also developed a pin mirror lens with 11 pin mirrors to improve the optical efficiency and quality with a thin lens. By combining the microdisplay with LetinAR’s pin mirror lens, we successfully demonstrated an AR device with a wide horizontal FoV of 46° but with a small form factor 4 mm lens.

Development of flexible transparent organic light-emitting devices (TOLEDs) still requires a number of advancements in transparent conducting electrodes with low reflection and absorption, a capping layer (CL) acting as refractive index-matching, and thin film encapsulation (TFE) with high water vapor barrier properties, among others. While substantial research has been reported on isolated examples in each area, there has been no detailed and systemic research related to the overall interactions of top electrodes, CLs, TFE, and their interfaces. In this work, TOLEDs have been fabricated with a thin Ag top electrode and CLs of different surface energy, which was encapsulated with high water vapor barrier property (1.35Ⅹ10−4 gm−2day−1 at 37.8 °C and 100 % RH). The encapsulation barrier was comprised of 50-nm-thick Al2O3 thin films deposited using a low-temperature (95 °C) ALD process. Once prepared, the TOLEDs were studied using a variety of techniques to determine the enhancements to electrical, optical, and water vapor barrier properties. Although the nature of the CL materials affects the film formation on the top electrode layer, there is no impact on the properties of the Al2O3 thin films. In the formation process of the Al2O3 TFE, the device incorporating a tris(8-hydroxyquinoline)aluminum (Alq3) CL showed superior performance, whereas device performance degredation was noted with the 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HATCN) CL. The lack of degradation in the Alq3 CL device during ALD processing is attributed to the high thermal stability of Alq3, which exhibits a high glass transition temperature of 175 °C. However, in the HATCN CL device, it is expected that formation of aromatic radical anions [HAT(CN)6]•− and dianions [HAT(CN)6]2−, and/or band bending of fermi energy of the HATCN at the interface of the thin Ag layer, results in the observed degraded performance.

We fabricated simple and color-stable phosphorescent white organic light-emitting diodes (OLEDs) without an interlayer using a single host of 1,3-bis(9-carbazolyl)benzene with iridium(III) bis[(4,6-difluorophenyl) pyridinato-N,C2’]picolinate and bis(1-phenylisoquinoline)(acetylacetonate) iridium(III) as blue and red phosphorescent emitters, respectively. The CIE 1931 color coordinate difference of the white OLEDs is (0.008, 0.007) when the luminance of the device is increased from approximately 265 cd/m2 to 9156 cd/m2, which is regarded as visually indistinguishable in practice. In addition, we also measured the decay time of excitons to investigate the emission mechanism in this device using transient photoluminescence and electroluminescence techniques.

Thin-film transistor (TFT)-driven full-color organic light-emitting diodes (OLEDs) with vertically stacked structures are developed herein using photolithography processes, which allow for high-resolution displays of over 2,000 pixels per inch. Vertical stacking of OLEDs by the photolithography process is technically challenging, as OLEDs are vulnerable to moisture, oxygen, solutions for photolithography processes, and temperatures over 100 °C. In this study, we develop a low-temperature processed Al2O3/SiNx bilayered protection layer, which stably protects the OLEDs from photolithography process solutions, as well as from moisture and oxygen. As a result, transparent intermediate electrodes are patterned on top of the OLED elements without degrading the OLED, thereby enabling to fabricate the vertically stacked OLED. The aperture ratio of the full-color-driven OLED pixel is approximately twice as large as conventional sub-pixel structures, due to geometric advantage, despite the TFT integration. To the best of our knowledge, we first demonstrate the TFT-driven vertically stacked full-color OLED., To realize organic light-emitting diodes (OLEDs) with improved resolution for display applications, a method for achieving high yield device fabrication is needed. Here, the authors report vertically-stacked transistor-driven full-color OLEDs with photolithography-processed intermediate electrodes.

Poly(dimethylsiloxane) has attracted much attention in soft lithography and has also been preferred as a platform for a photochemical reaction, thanks to its outstanding characteristics including ease of use, nontoxicity, and high optical transmittance. However, the low stiffness of PDMS, an obvious advantage for soft lithography, is often treated as an obstacle in conducting precise handling or maintaining its structural integrity. For these reasons, a Glass-PDMS-Glass structure has emerged as a straightforward alternative. Nevertheless, several challenges are remaining in fabricating Glass-PDMS-Glass structure through the conventional PDMS patterning techniques such as photolithography and etching processes for master mold. The complicated techniques are not suitable for frequent design modifications in research-oriented fields, and fabrication of perforated PDMS is hard to achieve using mold replication. Herein, we utilize the successive laser pyrolysis technique to pattern thin-film PDMS for microfluidic applications. The direct use of thin film at the glass surface prevents the difficulties of thin-film handling. Through the precise control of photothermal pyrolysis phenomena, we provide a facile fabrication process for perforated PDMS microchannels. In the final demonstration, the laminar flow has been successfully created owing to the smooth surface profile. We envision further applications using rapid prototyping of the perforated PDMS microchannel.

Quantum dot light-emitting diodes (QLEDs) are one of the most promising candidates for next-generation displays and lighting sources, but they are barely used because vulnerability to electrical and thermal stresses precludes high brightness, efficiency, and stability at high current density (J) regimes. Here, bright and stable QLEDs on a Si substrate are demonstrated, expanding their potential application boundary over the present art. First, a tailored interface is granted to the quantum dots, maximizing the quantum yield and mitigating nonradiative Auger decay of the multiexcitons generated at high-J regimes. Second, a heat-endurable, top-emission device architecture is employed and optimized based on optical simulation to enhance the light outcoupling efficiency. The multilateral approaches realize that the red top-emitting QLEDs exhibit a maximum luminance of 3 300 000 cd m-2 , a current efficiency of 75.6 cd A-1 , and an operational lifetime of 125 000 000 h at an initial brightness of 100 cd m-2 , which are the highest of the values reported so far.

From the very first time that graphene was used as a transparent electrode for OLED applications, the emergence of active-matrix (AM)-graphene OLED displays has been envisioned. Realizing this expectation, however, turned out to be difficult. Two obstacles are the growth and transfer of a large-area graphene film and the patterning of a graphene film into pixels. To solve these problems, a process of patterning a graphene film without surface contamination was developed. The fabrication of OLED panels by the patterned graphene anode on Gen 2(370 × 470 mm)-sized and flexible substrates was successfully demonstrated. In this work, oxide TFT arrays were combined as a switching backplane, and a pixelated graphene OLED was used as an emissive layer, to realize AM-graphene OLED displays. To explore the technical feasibility of flexible AM-graphene OLED displays, the aforementioned components were formed on a flexible substrate. For commercial-level production, all the processes that were used were chosen to be compatible with the conventional display processes.

Microdisplay is a key technology for realizing augmented reality (AR) and mixed reality (MR) devices, which have attracted much attention of late. Even though the operating voltage in the tandem structure is higher than that in the single structure, 2-stack tandem OLED exhibited 20,000 cd/m2 at 9 V, which is compatible with CMOS circuit driving. Due to its top-emitting geometry with a tandem structure, the OLED device with a well-controlled thickness exhibited a white spectrum with (0.26, 0.26) color coordinates. The pixel density of the fabricated microdisplay panel with a white tandem OLED was about 2350 pixels per inch, and the active area of the panel was 0.7 inch diagonally. The resolution of the panel was 1280 × 1024, corresponding to SXGA, and the maximal luminance was 3,000 cd/m2.

Surface-exchanged, partially pyridine-functionalized colloidal quantum dot-based light-emitting diodes (QD-LEDs) that exhibit a low turn-on voltage and high brightness are reported. Pyridine is stochastically exchanged to a greater extent at the interface between the QDs and the hole transport layer via ligand exchange. Pyridine improves the charge balance within the QDs by enhancing the hole injection and hence lowers the turn-on voltage of the QD-LEDs. This strategy is applied to red-, green-, and blue-emitting (three primary colors) QD-LEDs. Pyridine-functionalized QD-LEDs (QD/py-LEDs) show enhanced maximum luminance, lowered driving voltages, and improved current- and power-efficiencies as compared with the original surface ligand-functionalized QD-LEDs. All three types of QD/py-LEDs show narrow emission spectra (full width at half maximum

Electrical annealing (EA) is one of the post treatments to enhance the electrical performances of organic devices. To date, the improvements using EA have only been reported for the solution-processed devices because its mechanism has been known as the alignments of ionic impurities or polymer chains. In this paper, we applied EA to thermally evaporated organic diodes which not have ionic impurities or polymer chains. After EA, the turn-on voltage of the diode was reduced, and the forward-bias current of the diode was increased without changing the reverse-bias current, resulting in an improvement of the cutoff frequency of the rectifier. In addition, we proposed a new mechanism to explain why the EA can be applied to the thermally evaporated organic devices. Based on time-of-flight secondary ion mass spectrometry and impedance spectra, we suggest that this improvement is due to the creation of a MoO3:pentacene mixed layer, leading to ease of charge injection. We believe that our finding will be helpful to understand change at the organic/metal interfaces and useful to apply a wide range of organic devices such as organic photovoltaics, organic light-emitting diodes, and organic thin-film transistors.

Herein, the color gamut change by optical crosstalk between sub-pixels in high-resolution full-color organic light-emitting diode (OLED) microdisplays was numerically investigated. The color gamut of the OLED microdisplay decreased dramatically as the pixel density of the panel increased from 100 pixels per inch (PPI) to 3000 PPI. In addition, the increase in thickness of the passivation layer between the bottom electrode and the top color filter results in a decrease in the color gamut. We also calculated the color gamut change depending on the pixel structures in the practical OLED microdisplay panel, which had an aspect ratio of 32:9 and a pixel density of 2,490 PPI. The fence angle and height, refractive index of the passivation layer, black matrix width, and white OLED device structure affect the color gamut of the OLED microdisplay panel because of the optical crosstalk effect.

We investigated the optical reflectance, surface roughness, and sheet resistance of aluminum (Al)/titanium nitride (TiN), titanium (Ti), and tungsten (W) layers on Si substrates, which are available in the CMOS foundry, for organic light-emitting diode (OLED) microdisplays. The devices with different metal anode layers exhibited different hole-injection properties and OLED performances, owing to the different optical and electrical properties of metal anode layers. Based on the OLED characteristics, the Al/TiN layer was selected as an anode layer for OLED microdisplays. A green monochromatic OLED microdisplay panel was designed and implemented using the 0.11-μm CMOS process. The density of pixels was ~2 351 pixels per inch and the panel's active area was 0.7 in in diagonal. The resolution of the panel was 1 280 × 3 × 1 024, corresponding to SXGA. The panel was successfully operated, and the maximal luminance was ~460 cd/m2.

Pleurotus eryngii produces various functional molecules that mediate physiological functions in humans. Recently, we observed that P. eryngii produces molecules that have antidepressant functions. An ethanol extract of the fruiting body of P. eryngii was obtained, and the extract was purified by XAD-16 resin using an open column system. The ethanol eluate was separated by HPLC, and the fraction with an antidepressant function was identified. Using LC-MS, the molecular structure of the HPLC fraction with antidepressant function was identified as that of tryptamine, a functional molecule that is a tryptophan derivative. The antidepressant effect was identified from the ethanol extract, XAD-16 column eluate, and HPLC fraction by a serotonin receptor binding assay and a cell-based binding assay. Furthermore, a forced swimming test (FST) showed that the mice treated with purified fractions of P. eryngii exhibited decreased immobility time compared with nontreated mice. From these results, we suggest that the extract of P. eryngii has an antidepressant function and that it may be employed as an antidepressant health supplement.

The charge injection imbalance into the quantum dot (QD) emissive layer of QD-based light-emitting diodes (QD-LEDs) is an unresolved issue that is detrimental to the efficiency and operation stability of devices. Herein, an integrated approach to harmonize the charge injection rates for bright and stable QD-LEDs is proposed. Specifically, the electronic characteristics of the hole transport layer (HTL) is delicately designed in order to facilitate the hole injection from the HTL into QDs and confine the electron overflow toward the HTL. The well-defined exciton recombination zone by the engineered QDs and HTL results in high performance with a peak luminance exceeding 410 000 cd/m2, suppressed efficiency roll-off characteristics (ΔEQE < 5% between 200 and 200 000 cd/m2), and prolonged operational stability. The electric and optoelectronic analyses reveal the charge carrier injection mechanism at the interface between the HTL and QDs and provides the design principle of QD heterostructures and charge transport layers for high-performance QD-LEDs.

Based on its outstanding mechanical, thermal, and chemical properties, a Polyimide (PI) is useful in a wide range of applications. Its usage in biomedicine is drawing great attention owing to the recent confirmation of the biocompatibility of various PIs. However, the conventional patterning of a PI, based on photolithographic methods, which is expensive and time-consuming, hampers the rapid advancement of research-oriented fields that require frequent design changes. To resolve this problem, we introduce the method of the monolithic digital patterning of PI up to the quasi-three-dimensional (3D) structures at the microscale resolution by laser-induced jetting of highly porous Laser-induced graphene (LIG) from the PI matrix. Pyrolytic jetting of the LIG is dependent not only on the laser-induced temperature but also on its temporal and spatial gradients. However, the surfaces of the remaining PI can be exceptionally smooth at the optimum laser condition, comparable to the pristine surface at the microscopic level, as confirmed by Raman spectroscopy and Atomic force microscopy (AFM) measurements. On-demand microfluidic channels and multilevel imprinting molds are created in a single step using the proposed method as a proof-of-concept, substantiating its potential application in relevant research.

Presented is a flexible dual-mode display operable in reflective and emissive mode according to ambient light for optimal visibility on a nonplanar surface. Flexible-backplane-embedding organic light-emitting diodes (OLEDs), thin-film transistors (TFTs), and control electrodes for liquid crystal (LC) shutter are realized by the laser lift-off (LLO) method and the newly developed polyimide (PI) delamination technique. A novel color-filterless LC shutter with color dyes is merged with this flexible backplane for operation in reflective mode. This work opens up a promising approach to building displays that are adaptive to the surrounding environment for better usability.

We demonstrate a Cu(I) and Cu(II) codoped nickel(II) oxide (NiOx) hole injection layer (HIL) for solution-processed hybrid organic-inorganic light-emitting diodes (HyLEDs). Codoped NiOx films show no degradation on optical properties in the visible range (400–700 nm) but have enhanced electrical properties compared to those of conventional Cu(II)-only doped NiOx film. Codoped NiOx film shows an over four times increased vertical current in comparison with that of NiOx in conductive atomic force microscopy (c-AFM) configuration. Moreover, the hole injection ability of codoped NiOx is also improved, which has ionization energy of 5.45 eV, 0.14 eV higher than the value of NiOx film. These improvements are a consequence of surface chemical composition change in NiOx due to Cu cation codoping. More off-stoichiometric NiOx formed by codoping includes a large amount of Ni vacancies, which lead to better electrical properties. Density functional theory calculations also show that Cu doped NiO model structure with...

With increasing demand for transparent conducting electrodes, graphene has attracted considerable attention, owing to its high electrical conductivity, high transmittance, low reflectance, flexibility, and tunable work function. Two faces of single-layer graphene are indistinguishable in its nature, and this idea has not been doubted even in multilayered graphene (MLG) because it is difficult to separately characterize the front (first-born) and the rear face (last-born) of MLG by using conventional analysis tools, such as Raman and ultraviolet spectroscopy, scanning probe microscopy, and sheet resistance. In this paper, we report the striking difference of the emission pattern and performance of transparent organic light-emitting diodes (OLEDs) depending on the adopted face of MLG and show the resolved chemical and physical states of both faces by using depth-selected absorption spectroscopy. Our results strongly support that the interface property between two different materials rules over the bulk property in the driving performance of OLEDs.

We report a semi-transparent temperature sensor for fingerprint liveness detection on an organic light-emitting diode (OLED). Solution-processable graphene oxide was coated between two indium tin oxide electrodes on a glass substrate, and a semi-transparent reduced graphene oxide (rGO) temperature sensor was successively fabricated through graphene oxide (GO) reduction using a laser source. The rGO temperature sensor showed a resistance variance characteristic of 80 % compared to the initial resistance when heated from 15 °C to 170 °C. When finger was touched on the rGO temperature sensor, the resistance variation was 0.5 % and 7 % at 35 °C and 50 °C, respectively. In addition, GO was coated on the light-emitting side of green phosphorescent OLEDs to investigate the damage caused by photothermal reduction energy. The OLEDs irradiated by the laser source for GO reduction showed nearly the same current–voltage characteristics and electroluminescence spectrum as the device without laser irradiation, although the luminance of the device decreased due to the absorption of rGO.