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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.

Despite the fact that research into most high-performance thermoelectric (TE) materials is focused on tellurides, compelling demand has arisen to replace tellurium (Te) with selenium (Se) due to the scarcity of Te. Silver bismuth diselenide (AgBiSe2, ABS) has been widely studied in relation to thermoelectric applications due to its intrinsically low thermal conductivity. However, its low power factor (PF) has been considered as an underlying issue preventing improvements of the TE properties of ABS. Here, it is demonstrated that a high PF can be achieved by incorporating Cu into the ABS system via the nestification of conduction bands when a disordering between Ag and Bi occurs. Degenerate electronic bands simultaneously increase the density-of-states effective mass and carrier concentration while not reducing the carrier mobility significantly. Therefore, improved TE performance with a maximum PF of 8.2 μW cm−1 K−2 and a peak zT value of 1.14 was achieved at 773 K, opening a new horizon for the development of environmentally benign TE materials with high performance capabilities.

Alzheimer's disease (AD), the most common age-related neurodegenerative disorder, accompanies a massive degradation of neurons including axonal injury. Being an axonal neuron-specific protein, neurofilament light (NfL) is a blood biomarker that reflects the neurodegeneration in AD, but no attempt has been made yet to develop sensing platforms that target NfLs in blood serum or plasma. Here, we report three-dimensional cross-stacked Pt nanowire arrays for the ultrasensitive photoelectrochemical (PEC) detection of NfLs. We constructed a woodpile-like Pt nanowire array (PtWP)-based biocathode by printing multilayer Pt nanowire arrays in an orthogonal configuration and conjugating them with NfL-specific DA2 antibodies. According to our collective electrochemical analyses, the five-layered PtWP electrode modified with DA2 antibodies exhibited high oxygen reduction activities due to the large electrochemical active surface area and the effective electron transfer properties. We have combined the DA2-PtWP biocathode with a water-oxidizing, iron oxyhydroxide-deposited bismuth vanadate (FeOOH/BiVO

We have prepared a highly luminescent quantum dot (QDs)-TiO2 nanocomplex film by the dip coating method. Because QDs with 3-mercaptopropionic acid as a ligand adsorb ionized Ti+ cations on the TiO2 particle, the average distance between the QDs can be changed through controlling the porosity in the film. The porosity is controlled using ethyl cellulose (EC). EC is the best material for well dispersing the hydroxyl functional group (–OH) in the chemical structure, and forming pores inside the film under the decomposition temperature (above 698 °F). As the porosity decreases, the average decay time controlled by the porosity increases to the maximum 91.2 ns. On the other hand, the amount of QDs decreased to 50%, hindering the increase of photo-luminescence (PL) intensity. Through this result, we have found that the PL intensity of the QD films is strongly related to the amount of the QDs and the resolution of aggregation. Consequently, we have optimized the porosity of the film and obtained high PL intensities up to approximately 17 times.

Despite highly promising characteristics of three-dimensionally (3D) nanostructured catalysts for the oxygen evolution reaction (OER) in polymer electrolyte membrane water electrolyzers (PEMWEs), universal design rules for maximizing their performance have not been explored. Here we show that woodpile (WP)-structured Ir, consisting of 3D-printed, highly-ordered Ir nanowire building blocks, improve OER mass activity markedly. The WP structure secures the electrochemically active surface area (ECSA) through enhanced utilization efficiency of the extended surface area of 3D WP catalysts. Moreover, systematic control of the 3D geometry combined with theoretical calculations and various electrochemical analyses reveals that facile transport of evolved O2 gas bubbles is an important contributor to the improved ECSA-specific activity. The 3D nanostructuring-based improvement of ECSA and ECSA-specific activity enables our well-controlled geometry to afford a 30-fold higher mass activity of the OER catalyst when used in a single-cell PEMWE than conventional nanoparticle-based catalysts., Improved design of three-dimensionally nanostructured catalysts for oxygen evolution reaction (OER) can play a key role in maximizing the catalytic performance. Here, the authors show that woodpile-structured iridium consisting of 3D-printed, highly-ordered nanowire building blocks significantly improve OER mass activity.

The next-generation wearable near-eye displays inevitably require extremely high pixel density due to significant decrease in the viewing distance. For such denser and smaller pixel arrays, the emissive material must exhibit wider colour gamut so that each of the vast pixels maintains the colour accuracy. Electroluminescent quantum dot light-emitting diodes are promising candidates for such application owing to their highly saturated colour gamuts and other excellent optoelectronic properties. However, previously reported quantum dot patterning technologies have limitations in demonstrating full-colour pixel arrays with sub-micron feature size, high fidelity, and high post-patterning device performance. Here, we show thermodynamic-driven immersion transfer-printing, which enables patterning and printing of quantum dot arrays in omni-resolution scale; quantum dot arrays from single-particle resolution to the entire film can be fabricated on diverse surfaces. Red-green-blue quantum dot arrays with unprecedented resolutions up to 368 pixels per degree is demonstrated., Designing quantum dot light emitting diodes with full-colour pixel arrays with sub-micron feature size remains a challenge. Here, the authors demonstrate red-green-blue quantum dots arrays with resolutions up to 368 pixels per degree by leveraging thermodynamic-driven immersion transfer-printing.

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...

Environmentally friendly ZnSe/ZnS core/shell quantum dots (QDs) as an alternative blue emission material to Cd-based QDs have shown great potential for use in next-generation displays. However, it remains still challenging to realize a high-efficiency quantum dot light-emitting diode (QLED) based on ZnSe/ZnS QDs due to their insufficient electrical characteristics, such as excessively high electron mobility (compared to the hole mobility) and the deep-lying valence band. In this work, the effects of QDs doped with hole transport materials (hybrid QDs) on the electrical characteristics of a QLED are investigated. These hybrid QDs show a p-type doping effect, which leads to a change in the density of the carriers. Specifically, the hybrid QDs can balance electrons and holes by suppressing the overflow of electrons and improving injection of holes, respectively. These electrical characteristics help to improve device performance. In detail, an external quantum efficiency (EQE) of 6.88% is achieved with the hybrid QDs. This is increased by 180% compared to a device with pure ZnSe/ZnS QDs (EQE of 2.46%). This record is the highest among deep-blue Cd-free QLED devices. These findings provide the importance of p-type doping effect in QD layers and guidance for the study of the electrical properties of QDs.

Solution-processable charge injection materials have gathered considerable attention in the field of organic optoelectronics owing to their ability to enhance device efficiency. Of those candidates, polyethylenimine (PEI) polymers have been widely explored, but their effect on the device physics in organic light-emitting diodes (OLEDs) are not completely elucidated yet. In this work, the impact of ZnO:PEI hybrid nanocomposite as an electron injection layer (EIL) of OLEDs on the device performance is investigated. Two different PEIs with the different spatial molecular configuration of the polymer, either linear or branched-type, are employed. Both PEI polymers have the ability to effectively reduce the work-function of ZnO. The ZnO:linear-PEI EIL shows higher device efficiency in comparison to the ZnO:branched-PEI EIL in the charge-balanced OLEDs, whereas the results are opposite in the charge-imbalanced device setup. This is mainly due to the different role required of EIL materials upon different device working mechanisms. This work shows a series of experimental results of the detailed device characteristics using ZnO:PEI hybrid EILs in order to provide a systematic understanding of the device physics by combining two key concepts together; (1) control of the molecular configuration, and (2) charge carrier dynamics.