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To fabricate electrodes for use in flexible electronic devices with improved resistance to the mechanical stresses induced by repeated bending, we developed a highly flexible and conductive composite comprised of Ti3C2-based MXene nanosheets and Ag nanoparticles. Specifically, we synthesized Ti3C2-based MXene nanosheets and added them as a second filler to an Ag dispersion to fabricate Ag–MXene composite paste. Although the synthesized MXene nanosheets are somewhat less electrically conductive than pure Ag nanoparticles, the conductivity of the pattern formed by printing this composite paste was comparable to that of pure Ag nanoparticle-based electrode. Moreover, resistance in the resulting electrode remained fairly constant despite repeated bending employing a curvature radius of 2 mm. We attribute this to the presence of the MXene nanosheets, whose homogeneously distributed hydroxyl or oxygen terminate surface functional groups prevented or delayed the propagation of cracks inside the printed pattern despite repeated bending.

A self-healable and stretchable light-emitting device with high emission characteristics was developed. To this end, a reversibly crosslinkable polyurethane (rcPU) was synthesized, and ZnS:Cu microparticles were dispersed therein to form an alternating current-driven electroluminescent (EL) film. Transparent electrodes were formed on both surfaces of the EL film for voltage application by using Ag nanowires, which were impregnated under the polymer surface by inverted layer processing and vaporized solvent-assisted embedding method. The developed device exhibited an exceptionally high maximum emission intensity of almost 500 cd/m2. In addition, the device maintained its homogeneous emission characteristics even after the application of 100% uniaxial strain with a luminance degradation of less than 40%. Due to the reversible crosslinking characteristics of the rcPU, the device could be recombined even after being completely cut, and the emission properties before cutting could be restored.

Upon Cu doping into host semiconductor quantum dots (QDs), intra-gap states inside the band gap are generated, by which energy down-shifted photoluminescence (PL) with broad emissivity and large Stokes shift emerges. Technologically important, environmentally friendly InP QDs typically used as green and red emitters in display devices can achieve exceptional PL quantum yields (QYs) of near-unity (95–100%) when the-state-of-the-art core/shell heterostructure of the ZnSe inner/ZnS outer shell is elaborately applied. Meanwhile, the PL QYs of red-to-near-infrared (IR)-emitting Cu-doped InP (InP:Cu) QDs reported to date are still modest (40–58%). Herein, we explore the synthesis of strain-engineered highly emissive InP:Cu/Zn–Cu–In–S (ZCIS)/ZnS core/shell/shell QDs via a one-pot approach. When this unconventional combination of a ZCIS/ZnS double shelling scheme is introduced to a series of InP:Cu cores with different sizes, the resulting InP:Cu/ZCIS/ZnS QDs with a tunable near-IR PL range of 694–850 nm yield the highest-ever PL QYs of 71.5–82.4%. These outcomes strongly point to the efficacy of the ZCIS interlayer, which makes the core/shell interfacial strain effectively alleviated, toward high emissivity. The presence of such an intermediate ZCIS layer is further examined by comparative size, structural, and compositional analyses.

This report discusses the effect of speckle size on the quality of holographic images based on a liquid-crystal-on-silicon (LCoS) spatial light modulator (SLM). Further, it proposes methods of quantifying the average speckle size and holographic image resolution. These methods enable both characteristics to be compared using the same unit (the number of pixels in the holographic image), providing an intuitive and effective comparative analysis method. In particular, by varying the LCoS resolution ratio, the change in the resolvable minimum pixels of the holographic image is interpreted in conjunction with the average speckle size; moreover, an analysis of the correlation between the latter two is presented. This approach, based on LCoS resolution division, could provide useful insights into single-SLM-based, full-color holographic displays using space division. Furthermore, it could be extended to other components, including more advanced LCoS SLMs, and used to identify the relative effects on image quality with speckles.

As the interest in foldable smartphones recently launched onto the market shifts toward the next generation of flexible electronics, the development of ultrathin devices is gaining considerable attention. The strain formed on the surfaces of film-based devices approximates the film thickness divided by twice the radius of curvature; therefore, the use of an ultrathin substrate is the key for the development of next generation foldable devices. However, the stiffness of ultrathin films is extremely low; thus, it cannot be easily used directly as a substrate for device fabrication. Therefore, these films generally undergo device manufacturing processes while being attached to a rigid substrate such as glass and are peeled from the rigid substrate after the process is finished. Thus, the initial adhesion of the adhesive used to fix the film to the temporary substrate should be strong, and after the process is completed, the adhesion must be lessened to enable soft peeling. In this study, we succeeded in developing a novel pressure-sensitive adhesive (PSA) whose adhesive strength can be severely reduced by water treatment. Accordingly, considering that amphiphilic oligomers promote water absorption through hydrogen bonding to water, amphiphilic oligomers were mixed with an acrylic polymer to prepare the water-responsive PSA (wr-PSA). The adhesion strength of the wr-PSA in the early stage, which reached 382(±22) N/m, dramatically dropped to 9(±2) N/m after a water immersion test. Using the wr-PSA, a 1.4 μm-thick polyethylene terephthalate film coated with Ag nanowires was softly peeled off from the glass after being immersed in warm water. In addition, the adhesion reduced by the immersion in water was recovered again when the water absorbed by the adhesive was dried. This implies that the developed adhesive can be reusable.

A transparent light emitting diode (LED) panel with a 16 × 16 multicolor LED array for a signage application is proposed and studied based on experimental and simulation results. As a transparent electrode, oxide/metal/oxide (OMO) trilayers with various Al interlayer thicknesses were fabricated and characterized using an established a simulation model. Using commercial ray tracing optical and SPICE simulation tools, we designed the LED panel and investigated in its optical and electrical properties. Moreover, in order to resolve the waveguide effect and voltage drop issue across the panel, we integrated additional optical structures and various OMO width into the design. The results show that the OMO electrode interconnects and proposed design considerations are pivotal aspects toward achieving transparent LED digital signage applications.

A reversibly cross-linkable and transparent polymer featuring stretchability and thermal healability is prepared by introducing Diels-Alder (DA)-reactive moieties into polydimethylsiloxane (PDMS), namely, a healable PDMS (h-PDMS). Inspired by the fact that retro-DA reactions occur even at low temperatures (albeit at a low rate), we maximize the effectiveness of small reactant products, demonstrating that self-healing and self-integration realized by 1-3 min exposure of cured h-PDMS to methyl ethyl ketone (MEK) vapor is more efficient than that achieved by direct sample heating at high temperatures. This technology is first used to uniformly transfer Ag nanowires (Ag NWs) formed on a temporary substrate to the h-PDMS surface, and further MEK vapor treatment allows the transferred NWs to be impregnated below the h-PDMS surface to afford an in-plane strain sensor. Most importantly, the developed method is used to perfectly integrate two identical Ag NW/h-PDMS films and thus place NWs on a neutral plane. Consequently, because of the unique structure in which a percolated network of AgNWs is formed on the interface where the two identical h-PDMS films are chemically integrated, the fabricated sensor is transparent, self-healable, stretchable, and insensitive to bending but sensitively responds to in-plane strain induced by lateral deformation.

A light extraction structure and a flexible electrode have been developed to enhance the electroluminescence (EL) efficiency of flexible organic light-emitting diodes (FOLEDs). However, these structures are still influenced by optical losses, poor electrical stability, and low throughput, and are not suitable to be adopted into FOLEDs due to the surface roughness problem, low flexibility/adhesion, complicated process, and high temperature/pressure process. Here, to solve these problems, we demonstrate embedded Ag nanowires (AgNWs) in flexible substrate and highly flexible random nano pattern via easy/low-cost solution form process at atmospheric pressure and low temperature without any additional material. This study demonstrates an internal and external light extraction structure composed of double-sided nano-dimpled substrate PVB (DndP), which is directly fabricated on both sides of a flexible substrate (polyvinyl butyral, PVB) only in itself without additional material via the easy/low-cost transferring process using the anodic aluminum oxide (AAO) template by an anodization process-based solution form at atmospheric pressure and low temperature. Therefore, because the DndP and the substrate are composed of the same material, PVB, there is no light loss between their interfaces. In addition, a high-refractive-index TiO2 nanoparticle, for the scattering effect, and AgNWs, for electrode flexibility, are embedded into the DndP via the covering method using the solution form. Such structures exhibit extraordinary mechanical flexibility due to the AgNWs embedded in the PVB substrate. Therefore, FOLEDs using such structures can be well adapted to flexible/rollable/foldable displays and wearable application devices. Moreover, the corrugated surface of FOLEDs by such structures can improve the current flow through increased surface area of electrodes and extract the trapped light through the scattering effect (Rayleigh, Mie), reducing the total reflection and coupled photon in metal/dielectric. In addition, the FOLEDs with such structures show color/spectrum-stable property and independence of viewing angles owing to their random nature. The final green FOLEDs with DndP, embedded scattering TiO2 nanoparticle, and embedded AgNWs&PEDOT:PSS demonstrate an outstanding EL efficiency enhancement ratio of 2.23 time via internal and external light extraction without electrical short.

The high interest sparked by the foldable smartphones recently released on the market is gradually shifting to the next generation of flexible electronic devices, such as electronic skins in the form of stretchable thin films. To develop such devices, good mechanical flexibility of all components (including the substrate, electrode, and encapsulant) is critical. Various technologies have been developed to enhance the flexibility of these components; however, progress in developing interconnection methods for flexible and stretchable devices has been limited. Here, we developed an ultrafast photoinduced interconnection method that does not require any adhesive or surface treatment. This method is based on heating metal nanostructures using intense pulsed light (IPL) and the reversible cross-linking of polymers. First, we synthesized a stretchable, transparent, and free-standing polymer substrate that can be reversibly cross-linked, and then Ag nanowire (AgNW) networks were formed on its surface. This electrode was irradiated with IPL, which locally heated the AgNWs, followed by decomposition of the polymer via the retro-Diels-Alder reaction and recross-linking. Independently fabricated AgNW/polymer films were layered and irradiated three times with IPL to form a bonded sample with excellent joint quality and no increase in electrical resistance compared to a single electrode. Furthermore, the interconnected electrodes were stretchable and optically transparent. Even when more than 200% strain was applied in a peel test, no breakage at the joint was observed. This allowed us to successfully produce a stretchable, transparent, and bending-insensitive pressure sensor for various applications such as motion detectors or pressure sensor arrays.

Development of a thin and dry electrode for electrocardiography (ECG) is essential in order to prevent skin irritation, allergic reactions from electrolytic gel, and motion artifacts caused by relative motion between the electrodes and the skin. In this study, we have developed a composite electrode made from Ag nanowires (AgNWs) and polyvinyl butyral (PVB), prepared by inverted layer processing (ILP). The initial composite electrodes were mechanically stable, flexible, and transparent; however, most of the NWs were located beneath the surface of the PVB such that few conductive pathways were exposed and available to contact the skin. In order to resolve this issue, prior to transferring the AgNWs from the temporary glass substrate to the PVB, we irradiated the NWs with intensive pulsed light. This irradiation induced plasmonic heating of the AgNWs, which caused the NWs to sink towards the glass and form a dense layer on the temporary substrate. Subsequent ILP resulted in the fabrication of an AgNWs/PVB composite electrode that demonstrated significant surface coverage of conductive pathways available for stable electrical contact with skin. The resultant composite electrode is an improved ECG electrode that exhibits fewer motion artifacts compared to conventional Ag/AgCl-based wet electrodes since it is both dry and conformable.

Most intrinsically healable polymers feature a soft nature and high flowability that arise from the reversible formation of bonds (e.g., cross-linkages). Unfortunately, a trade-off relationship between mechanical strength and healing capability is observed for the majority of these polymers, which necessitates the search for better alternatives. Herein, we synthesized a urethane acrylate-based intrinsically healable material with enhanced mechanical properties, demonstrating that this enhancement originates from the presence of UV curing-produced dynamic urea bonds acting as reversible cross-linkages. The synthesized polymer was hybridized with silver nanowires (AgNWs) to afford a transparent pressure-sensitive e-skin capable of irradiation-induced healing, i.e., the heating of AgNWs by a series of intense pulsed light (IPL) irradiations allowed one to instantly and rapidly repair the cutting marks or scratches artificially formed on e-skin sensors. The healing ability was originated from the enhanced flowability and thermal expansion of the polymer during IPL irradiation. Consecutive cutting-healing cycling showed that the cutting marks formed at the same locations could be effectively repaired for up to five times. The fringing effect-associated capacitance of a AgNW tandem compound pattern significantly increased with increasing pressure applied to the sensor surface, and the electric function of damaged sensors was successfully restored by irradiation-induced healing.

The development of epidermal electronics, which provides precise measurement of various human physiological signals without reducing the quality of life, has encountered a serious delay in its practical application because of potential damage experienced during fabrication. Such damage occurs mainly because fabrication of the epidermal device is typically carried out after attaching an ultrathin or stretchable film onto a stiffer carrier substrate, and eventually peeling it from the carrier. Substrates used in epidermal electronics suffer from very low stiffness to bending and stretching, resulting in severe strain during stripping from the carrier substrate, where devices formed on its surface are also subjected to significant damage. When a device is fabricated using an adhesive with an excessively low adhesion strength, however, some parts of the soft film can be prematurely peeled from the carrier during device fabrication. We propose a UV-responsive transparent pressure-sensitive adhesive (PSA) to fabricate ultrathin devices without process-induced damage. We synthesised an acryl-based PSA and mixed it with UV-curable oligomers. The soft UV curable PSAs contract and become rigid when the oligomers in the PSAs are cured by UV irradiation. This dramatically reduces the adhesion strength to less than 1% of the initial value and consequently enables peeling from the carrier without deteriorating the properties of the devices formed on the ultrathin film. In this case, it is not necessary to fabricate the device by using more materials than necessary considering the performance degradation in advance. Using this method, we developed a transparent bending-induced pressure sensor, with light transmittance higher than 93.5% at 550 nm.

Although a percolated network of silver nanowires (AgNWs) is considered the most promising flexible transparent electrode because of its high conductivity, high transmittance, excellent flexibility, and facile patternability, it has encountered a serious delay in its application to most optoelectronic devices. Here, we analyzed the reasons and tried to resolve the current issues to achieve near-foldable transparent touch sensors by employing an inverted layer processing method. A hydroxylated polydimethylsiloxane (PDMS) was used as a preliminary substrate for deposition and patterning of AgNWs, and then the nanowires were completely transferred to the newest version of colorless polyimide (cPI) by hydrophobic recovery of the PDMS surface. For the first time, we designed an automatic apparatus for testing the foldability of the fabricated composite film by a spacer inserting method. The testing of various AgNWs/cPI films with this method revealed that the thickness reduction approach could be an efficient and powerful tool to attain near-foldable electrodes if the AgNWs are solidly adhered to the substrate. Based on these findings, we could successfully demonstrate a near-foldable touch sensor, which is capable of sensing human touches even in the folded state.

Recent studies have revealed that silver nanowires (AgNWs) are a promising material for highly flexible transparent electrodes. Here we introduce a novel photoinduced recyclable approach to AgNW patterning to overcome the issue of loss of material during fabrication of AgNW patterns, which is a leading factor in the high fabrication costs of AgNW-based electrodes. Our patterning scheme involves the selective irradiation of an AgNW/polymer composite with high-intensity pulsed light, followed by immersion of the sample in a liquid and an ultrasonication treatment. The nanowires that detach during sonication could be recycled, and the recycled AgNWs achieved comparable performance to that of pristine AgNWs. The recycled AgNWs were also superior to commercial indium tin oxide films and other competing materials. We successfully demonstrated a high performance transparent heater by employing the recyclable patterning method and recycled AgNWs.

This study utilizes the characteristics of an Ag nanowire (AgNW) that can rapidly generate heat under high energy pulsed light (HEPL) incidence. Upon HEPL irradiation, the AgNWs melted the polymer in contact with them owing to the instantaneous heat generation, thereby inducing wetting and adhesion properties; the areas unaffected by the HEPL irradiation could be easily peeled, as they were directly placed on the surface of the film without any physicochemical reactions. Thus, we easily fabricated a sensor comprising of tandem compound patterns of AgNWs on the polyurethane film surface, without employing photolithography, etching, lamination, or any additional materials. The capacitance formed in the electrode sensitively varied with the applied pressure, implying that it could be used as a stretchable and transparent pressure sensor.

Reversible bonding between polymer chains has been used primarily to induce self-healing of damaged polymers. Inspired by the dynamic nature of such bonding, we have developed a polyurethane equipped with dynamic urea bonds (PEDUB) that has high strength sufficient to make it be freestanding and have a healing capability and self-bonding property. This allowed subsequent heterogeneous multicomponent device integration of electrodes/substrate and light-emitting pixels into a light-emitting device. We first used the PEDUB to individually fabricate a highly stretchable electrode containing Ag nanowires and stretchable composites with ZnS-based particles. They were successfully assembled into a stretchable, waterproof electroluminescent (EL) device even under mild conditions (60 °C for 10 min) owing to the reversible exchange of urea bonds and low glass transition temperature of PEDUB. The assembled device with an AC-driven EL architecture retained excellent EL characteristics even after stretching, submersion in water, and cutting owing to the robust solid-state bonding interfaces induced by the dynamic urea bonds. Consequently, various shapes of the illuminating elastomer and an illuminated picture were realized for the first time using the mosaic-like assembly method. This first demonstration of multicomponent assembly paves the way for future stretchable multifunctional devices.

We demonstrate ultrathin (thickness 88% at 550 nm), and conformable pressure-induced bending sensors with unprecedented flexibility and stretchability, produced by developing a photo-induced pattern of silver nanowires (AgNWs) on a 1.4 μm-thick polyethylene terephthalate (PET) sheet. This patterning approach does not require any additional materials to form a patterned barrier for AgNW etching or to enhance the adhesion between the AgNWs and PET. Simple irradiation using pulsed light on a masked AgNWs/1.4 μm-thick PET assembly followed by sonication formed a finely patterned AgNW network well-adhered to the underlying PET without impacting the optical transparency of the ultrathin PET. A pressure-induced bending-sensitive capacitive sensor fabricated by this approach was extremely flexible and stretch-compatible up to 100% uniaxial strain. This sensor, based on a simple tandem compound pattern, was reproducible, durable, and 90% more sensitive than an elastomeric pressure sensor made using the same sensor design. The functionality of the developed sensor system was successfully demonstrated in a sensitive acupressure sensor mounted on a gloved fingertip, in which the capacitance coincidently varied with the force applied to the fingertip.

An elastomer-free, extremely thin (less than 2 μm), and highly transparent (higher than 95%) pressure–sensitive capacitor is successfully fabricated using a combination of polyvinyl butyral (PVB) and a percolated network of silver nanowires (AgNWs). The strong affinity of PVB to the polyvinyl pyrrolidone (PVP) layer, which capped the AgNWs, stabilizes the sensor mechanically to an extent that it can resist 100000 cycles of bending under a curvature radius of 200 μm. The strong hydrogen bonding interactions and entanglement of PVB chains make the cross-linked PVB freestanding and very strong, facilitating the reduction of the thickness to less than 2 μm. The capacitance is formed on an AgNW tandem compound electrode pattern by the fringing effect, which increases with an increase in the pressure-induced bending applied to the surface of the sensor. The sensitivity is three times higher than that of an elastomeric pressure sensor with the same sensor design. The use of the AgNW/PVB sensor as a wearable acupressure sensor and a transparent motion detector is successfully demonstrated.

Because of outstanding optical properties and non-vacuum solution processability of colloidal quantum dot (QD) semiconductors, many researchers have developed various light emitting diodes (LEDs) using QD materials. Until now, the Cd-based QD-LEDs have shown excellent properties, but the eco-friendly QD semiconductors have attracted many attentions due to the environmental regulation. And, since there are many issues about the reliability of conventional QD-LEDs with organic charge transport layers, a stable charge transport layer in various conditions must be developed for this reason. This study proposes the organic/inorganic hybrid QD-LEDs with Cd-free InP QDs as light emitting layer and inorganic ZrO2 nanoparticles as electron transport layer. The QD-LED with bottom emission structure shows the luminescence of 530 cd m−2 and the current efficiency of 1 cd/A. To realize the transparent QD-LED display, the two-step sputtering process of indium zinc oxide (IZO) top electrode is applied to the devices and this study could fabricate the transparent QD-LED device with the transmittance of more than 74% for whole device array. And when the IZO top electrode with high work-function is applied to top transparent anode, the device could maintain the current efficiency within the driving voltage range without well-known roll-off phenomenon in QD-LED devices.

We have successfully designed, fabricated, and tested transparent and stretchable capacitors using adhesive polydimethylsiloxane (a-PDMS), which not only solidly adheres to commercial 184 polydimethylsiloxane (184 PDMS) films but also conformally adheres to skin or other various curved material surfaces. First, two sheets of 184 PDMS impregnated with Ag nanowires (AgNWs) were prepared, followed by face-to-face lamination using a-PDMS, resulting in a capacitor with a sandwich structure consisting of 184 PDMS/AgNWs/a-PDMS/AgNWs/184 PDMS. The adhesion between a-PDMS and 184 PDMS was so strong that no interfacial fracture was observed between the two materials during peel tests. Even after repeatedly applying a strain of 75% to the sandwich structure (up to 1000 times), the deterioration of the electrical properties of the sensor was insignificant. The capacitance of the sensor was very sensitive to changes in applied strain and pressure. When the sensor was attached to the skin or a shoe heel using a-PDMS, the capacitance was also quite sensitive to changes in the movement of the human body.

This paper was published with a typographical error in Acknowledgments on page 86. The grant number NRF-2019M3C1B909055 should read NRF-2019M3C1B9090559.

Most photodetectors developed to date essentially measure photocurrents induced by the generation and separation of electron-hole pairs in semiconductors during irradiation. Although the above light detection method is well established, highly sensitive, and applicable to a broad range of semiconductor materials, it requires the presence of a stable and direct contact between the semiconductor and the electrode for accurate photocurrent measurements. In turn, this prerequisite necessitates the use of various costly processes for device fabrication (e.g., photolithography and vacuum deposition of semiconductors/metals) and complicates the development of flexible devices. Herein, inspired by the fact that the dielectric properties of certain materials can be changed by light irradiation, we dispersed ZnS/Cu semiconducting particles in poly(vinyl butyral) to prepare a free-standing composite film and formed two layers of Ag nanowire electrodes on both sides of the cured composite to fabricate a photodetector of a completely new type. The developed device exhibited a capacitance very sensitive to irradiation with light of a specific wavelength and additionally featured the advantages of simple structure/operation mechanism, mechanical flexibility, and transparency, not showing any signs of performance deterioration even after severe damage.

Network structures of metal nanowires are a promising candidate for producing a wide range of flexible electronic devices, but only if they can be suitably patterned and retained on various materials. Here we present a new approach to the patterning of metal nanowires by employing intense-pulsed-light (IPL) irradiation to reduce the process to just two steps: irradiation and the subsequent removal of nonirradiated nanowires. This ultrasimple method eliminates the need to employ chemical reagents for etching or improving the adhesion of nanowires, and is compatible with Ag nanowires (AgNWs), Cu nanowires (CuNWs), and most transparent polymers. Furthermore, it is not reliant on additional processes, such as coating, heating, developing, and etching to make a patterned nanowire structure. Using this simple method, ultraflexible and transparent devices such as touch sensor, heater and light emitting diode with an exceptionally high mechanical stability have been successfully fabricated. This new method is expected to be directly applicable to the fabrication of a wide range of high-performance, low-cost, biocompatible, and wearable devices.

A highly stretchable and transparent pressure sensor based on a single layer silver nanowire (AgNW) electrode was successfully fabricated. In order to achieve this, we synthesized a stretchable and transparent adhesive, polyurethane urea (PUU), which was designed to firmly adhere to the AgNWs by incorporating 2,2-bis(hydroxymethyl)butyric acid with a carboxylic group. A patterned AgNW-based sensing electrode could be completely transferred to a PUU film deposited on a poly(dimethylsiloxane) (PDMS) substrate, resulting in a AgNW/PUU/PDMS pressure-sensitive capacitor. The capacitance was developed on a AgNW tandem compound electrode pattern by the fringing effect, which decreased with increasing pressure applied to the surface of the sensor. The sensitivity did not significantly deteriorate, even when the sensor was stretched up to a strain of 35% or when the stretching was cycled up to 10 000 times. A wearable acupressure sensor with a pressure sensitive matrix of nine pixels was successfully demonstrated.

The present work shows the effect of ethanolamine surface treatment on inverted InP quantum dot light-emitting diodes (QD-LEDs) with inorganic metal oxide layers. In the inverted structure of ITO/ZnO/InP QDs/CBP/MoO3/Al, a sol-gel derived ZnO film was used as an electron transport layer (ETL) and MoO3 was used as a hole injection layer (HIL). First, ethanolamine was treated as a surface modifier on top of the ZnO electron transport layer. The optical performance of the QD-LED device was improved by the ethanolamine surface treatment. Second, low temperature annealing (

Semiconductor quantum dots (QDs) promise facile color tuning and high color saturation in quantum-dot light-emitting devices (QD-LEDs) by controlling nanoparticle size and size distribution. Here, we demonstrate how this promise can be practically realized for the cadmium-free InP/ZnSe/ZnS multishell quantum dots. We developed a set of synthesis conditions and core/shell compositions that result in QDs with green, yellow, and red emission color. The QD-LEDs employing these QDs show efficient electroluminescence (EL) with luminance up to 1800 cd/m2 and efficiency up to 5.1 cd/A. The color coordinates calculated from the EL spectra clearly demonstrate the outstanding color saturation as an outcome of the narrow particle size distribution. These results prove that the performance gap between cadmium-free and cadmium-based QDs in QD-LEDs is shrinking rapidly.

A highly flexible and transparent conductive electrode based on consecutively stacked layers of conductive polymer (CP) and silver nanowires (AgNWs) fully embedded in a colorless polyimide (cPI) is achieved by utilizing an inverted layer-by-layer processing method. This CP-AgNW composite electrode exhibits a high transparency of >92% at wavelengths of 450–700 nm and a low resistivity of 7.7 Ω ◻−1, while its ultrasmooth surface provides a large contact area for conductive pathways. Furthermore, it demonstrates an unprecedentedly high flexibility and good mechanical durability during both outward and inward bending to a radius of 40 μm. Subsequent application of this composite electrode in organic solar cells achieves power conversion efficiencies as high as 7.42%, which represents a significant improvement over simply embedding AgNWs in cPI. This is attributed to a reduction in bimolecular recombination and an increased charge collection efficiency, resulting in performance comparable to that of indium tin oxide-based devices. More importantly, the high mechanical stability means that only a very slight reduction in efficiency is observed with bending (

Vinyl-type polynorbornene copolymers (P1–P3) containing side-chain triarylborane and iridium moieties were prepared by palladium(II) catalyzed copolymerization of norbornene monomers bearing triarylborane (Mes2BPh, M1) and an iridium emitter ((ppy)2Ir(acac), ppy = 2-phenyl-pyridinato-C2,N; acac = acetylacetonato, M2). Copolymerization led to facile incorporation of the comonomers in a controlled manner depending on the feed ratio of the comonomers (4.0 mol%-Ir in P1; 6.7 mol%-Ir in P2; 12.4 mol%-Ir in P3). While solution PL spectra of the copolymers exhibited partial intra-chain energy transfer from the borane moiety to iridium, complete energy transfer occurred in the rigid matrix, such as at 77 K and in the film state. The LUMO level of the borane moiety (M1) was estimated to be 2.4 eV, which is lower than that of M2 and poly(N-vinylcarbazole) (PVK) (ca. 2.2 eV for both). Solution processed PhOLEDs (D1−D3) incorporating P1–P3 as an emissive material in the PVK host displayed good performance in the low current density region, but D1−D3 suffered severe efficiency roll-off with increasing current densities. Comparable performance of D2 with the device (D4) based on P2 emitter and PVK:PBD (2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) host suggested that a borane moiety in the emissive polymer chain plays an actual role in facilitating electron transport in the emissive layer.

Silver nanowire (AgNW) based transparent electrodes are inherently coarse and therefore typically are only ever weakly bonded to a substrate. A remarkable improvement in the characteristics of a AgNW network film has, however, been achieved through a simple and short process of irradiating it with intense pulsed light (IPL). This not only avoids any severe deterioration in the optical characteristics of the AgNW film, but also significantly improves its electrical conductivity, adhesion to a polymeric substrate, and ability to endure bending stress. Most important of all, however, is the finding that the surface roughness of AgNW networks can also be improved by radiation. In a series of measurements made of organic light emitting diodes fabricated using these treated electrodes, it was revealed that the leakage current can be notably reduced by IPL treatment.

Crack-based strain sensor systems have been known for its high sensitivity, but suffer from the small fracture strain of the thin metal films employed in the sensor which results in its negligible stretchability. Herein, we fabricated a transparent (>90% at 550 nm wavelength), stretchable (up to 100%), and sensitive (gauge factor (GF) of 30 at 100% strain) strain gauge by depositing an encapsulated crack-induced Ag nanowire (AgNW) network on a hydroxylated poly(dimethylsiloxane) (PDMS) film. Stretching the encapsulated AgNWs/PDMS resulted in the formation of a percolation network of nanowire ligaments with abundant percolation paths. The encapsulating polymer was designed to adhere strongly to both the AgNW and PDMS. The improved adhesion ensured the resistance of the crack-induced network of AgNWs varied reversibly, stably, and sensitively when stretched and released, at strains of up to 100%. The developed sensor successfully detected human motions when applied to the skin.

We demonstrated a new water motion active transducer (WMAT) without any external bias-voltage sources or additional processes, which critically limit the use of conventional passive capacitive transducers that convert mechanical motion into electric energy. From a simple structure, we successfully turned on an LED using various kinds of natural water motion. The WMAT, which has wide applicability, has good potential to be a candidate for generating sustainable electric energy.

Conventional photodetectors (PDs) are based on measuring photocurrent, which is formed by the separation of electron-hole pairs generated in semiconductors upon light irradiation, through electrodes in direct contact with the semiconductors. Such devices are usually fabricated through complicated and precise processes such as thin film formation by vacuum deposition and fine patterning by photolithography and etching. In addition, PDs have a drawback that the contact quality between the electrode and the semiconductor is easily affected by external stress applied to the device. These issues make it difficult to implement a mechanically flexible device driven by conventional sensing mechanisms. Here we report a simple structured PD based on a semiconductor particle-polymer composite layer surrounded by two facing transparent electrodes, inspired by the fact that the dielectric properties of certain semiconductors change upon light irradiation with a photonic energy greater than or equal to their bandgap. In order to realize this, we synthesized a transparent and stretchable polymer, polyurethane-urea (PUU), which is compatible with Ag nanowires (AgNWs) and polydimethylsiloxane (PDMS) used for implementing stretchable electrodes, and dispersed ZnS:Cu particles into the PUU to form a sensory layer. The fabricated composite surrounded by two facing AgNW-based transparent electrodes was transparent and stretchable, and the capacitance formed at the composite sensitively changed upon irradiation of light with a wavelength of 420 nm and a power of 1.2 mW/cm2 even when the device was stretched or cut in half.

Quantum dots are a highly attractive class of materials for the use in light-emitting devices, since they allow high color purity, facile tunability and solution-processing methods. Here, zinc selenide QDs are investigated for their suitability as emissive material in cadmium-free blue QD-LEDs. By adjusting the stoichiometry in the synthesis the emission wavelength can be tuned in the range of 390–435 nm. For the assembly of the QD-LED, the device setup was adjusted to the low-lying ZnSe valence band energy by choosing a suitable hole-transport material. A first promising QD-LED result is achieved showing the characteristic narrow QD emission peak with a luminance of 25 cd/m2.

We report on the effects of an oxide semiconductor as an electron transport layer (ETL) on a quantum dots light emitting diode (QD-LED). To improve the properties of QD-LED, we optimized the process parameters for the deposition and post-annealing steps of an oxide ETL. When zinc tin oxide (ZTO) was deposited by radio-frequency magnetron sputtering in a gas mixture of argon and oxygen (Ar : O2 = 2 : 1) and then annealed under 760 Torr O2 for 10 min, our QD-LED showed improved luminescence characteristics. Additionally, to overcome the problem of non-uniform luminescence, we optimized the concentration and process conditions of colloidal quantum dot materials. Finally, we fabricated QD-LED devices with luminescence of 4,874 cd/m2 and luminous efficiency of 2.68 cd/A.

Soluble chemically reduced graphene oxide (RGO)/poly(4-vinyl pyridine) (P4VP) assembly was attempted by totally noncovalent approach. Chemical reduction of P4VP/GO mixture by hydrazine produced soluble RGO/P4VP assembly with long term stability. Prepared RGO/P4VP assembly showed pH-dependent variation of optical transmittance. Transmittance of RGO/P4VP assembly solution at pH 2.0 dramatically increased more than 200% of transmittance of assembly at pH 6. This optical transmittance change was fully reversible. The detailed morphological features of assemble was evaluated by dynamic light scattering (DLS) and atomic force microscopy (AFM). It is estimated that RGO/P4VP assemblies were well separated each other at pH 6, enabling much higher optical absorption of RGO plates. At pH 2, protonation of pyridine ring occurs and this might hamper effective noncovalent interaction between RGO plate and protonated P4VP chains, forming bigger aggregates having less chance for optical absorption. This pH-dependent optical modulation of RGO/P4VP assembly can be useful for the designing of pH-sensor, removable nanocatalyst, and targeted drug delivery, etc. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2538-2543, 2013

The recent trend of energy-harvesting devices is an adoption of fabric materials with flexible and stretchable according to the increase of wearable electronics. But it is a difficult process to form a core structure of dielectric layer or electrode on fabric materials. In particular, a fabric-based energy-harvesting device in contact with water has not been studied, though there are many challenging issues including insulation and water absorption in a harsh environment. So we propose an effective method to obtain an electrical energy from the water contact using our new fabric energy harvesting device. Our water motion active transducer (WMAT) is designed to obtain electrical energy from the variable capacitance through the movement and contact of water droplet. In this paper, we succeeded in generating an electrical energy with peak to peak power of 280 μW using a 30 μL of water droplet with the fabric WMAT device of 70 mm × 50 mm dimension. Furthermore, we specially carried out spray-coating and transfer processes instead of the conventional spin-coating process on fabric materials to overcome the limitation of its uneven morphology and porous and deformable assembly.

We investigated the orthogonal solvent of CdSe/ZnS quantum dots in order to deposit poly-TPD hole transport layer without damages and enhance the performances of QD-LEDs. Using hexane and heptane as nonpolar organic solvent of QDs does not affect poly-TPD layer has found. 3 mg/ml in hexane shows highest luminance and current efficiency but creates non-uniform QD-layer because lower boiling point of hexane. The last we found that even different concentration of QDs in heptane show similar device performance.

We report Quantum Dot light-emitting diode(QD-LED) designed on transparent and flexible PEN substrate, which shows saturated red electroluminescence spectra with full-width half-maximum(FWHM) as narrow as 40nm and transmittance of 60% at 550nm. In order to make flexible and transparent device, we fabricated a set of devices through combination of various cathodes materials and substrates.

UNLABELLED Colloidal quantum dots (QD)-based solar cells with near infrared (NIR) emission have been investigated. Lead sulfide (PbS) QDs, which have narrow band-gap and maximize the absorption of NIR spectrum, were chosen as active materials for efficient solar cells. The inverted structure of indium tin oxide/titanium dioxide/PbS QDs/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)/silver (ITO/TiO2/PbS QDs/ PEDOT PSS/Ag) was applied for favorable electron and hole seperation from the PbS QD. Through the ligand exchange by 1,2-Ethanedithiol (EDT), the interparticle distance of the PbS QDs in thin film became closer and the performance of the PbS QD-based solar cells was improved. Our PbS QD-based inverted solar cells showed open circuit voltages (V(oc)) of 0.33 V, short circuit current density (J(sc)) of 10.89 mA/cm2, fill factor (FF) of 30%, and power conversion efficiency (PCE) of 1.11%. In our PbS QD-based multifunctional solar cell, the NIR light emission intensity was simply detected with photodiode system, which implies the potential of multi-functional diode device for various applications.