The demand for flexible and wearable electronic devices is increasing due to their facile interaction with human body. Flexible, stretchable and wearable sensors can be easily mounted on clothing or directly attached onto the body. Especially, highly stretchable and sensitive strain sensors are needed for the human motion detection. Here, we report highly flexible, stretchable and sensitive strain sensors based on the nanocomposite of silver nanowire (AgNW) network and PDMS elastomer in the form of the sandwich structure (i.e., AgNW thin film embedded between two layers of PDMS). The AgNW network-elastomer nanocomposite based strain sensors show strong piezoresistivity with tunable gauge factors in the ranges of 2 to 14 and a high stretchability up to 70%. We demonstrate the applicability of our high performance strain sensors by fabricating a glove integrated with five strain sensors for the motion detection of fingers and control of an avatar in the virtual environment.

Highly Stretchable and Sensitive Strain Sensor Based on Silver Nanowire–Elastomer Nanocomposite

The present invention provides a heterocyclic compound and an organic light-emitting device including the heterocyclic compound. The organic light-emitting devices using the heterocyclic compounds have high-efficiency, low driving voltage, high luminance and long lifespan.

Organic light-emitting device

Optical transparency, tunable conducting properties and easy processability make metal oxides key materials for advanced optoelectronic devices. This Review discusses recent advances in the synthesis of these materials and their use in applications. Metal oxides (MOs) are the most abundant materials in the Earth's crust and are ingredients in traditional ceramics. MO semiconductors are strikingly different from conventional inorganic semiconductors such as silicon and III–V compounds with respect to materials design concepts, electronic structure, charge transport mechanisms, defect states, thin-film processing and optoelectronic properties, thereby enabling both conventional and completely new functions. Recently, remarkable advances in MO semiconductors for electronics have been achieved, including the discovery and characterization of new transparent conducting oxides, realization of p-type along with traditional n-type MO semiconductors for transistors, p–n junctions and complementary circuits, formulations for printing MO electronics and, most importantly, commercialization of amorphous oxide semiconductors for flat panel displays. This Review surveys the uniqueness and universality of MOs versus other unconventional electronic materials in terms of materials chemistry and physics, electronic characteristics, thin-film fabrication strategies and selected applications in thin-film transistors, solar cells, diodes and memories.

Metal oxides for optoelectronic applications

During the last few years, transition metal oxides (TMO) such as molybdenum tri-oxide (MoO3), vanadium pent-oxide (V2O5) or tungsten tri-oxide (WO3) have been extensively studied because of their exceptional electronic properties for charge injection and extraction in organic electronic devices. These unique properties have led to the performance enhancement of several types of devices and to a variety of novel applications. TMOs have been used to realize efficient and long-term stable p-type doping of wide band gap organic materials, charge-generation junctions for stacked organic light emitting diodes (OLED), sputtering buffer layers for semi-transparent devices, and organic photovoltaic (OPV) cells with improved charge extraction, enhanced power conversion efficiency and substantially improved long term stability. Energetics in general play a key role in advancing device structure and performance in organic electronics; however, the literature provides a very inconsistent picture of the electronic structure of TMOs and the resulting interpretation of their role as functional constituents in organic electronics. With this review we intend to clarify some of the existing misconceptions. An overview of TMO-based device architectures ranging from transparent OLEDs to tandem OPV cells is also given. Various TMO film deposition methods are reviewed, addressing vacuum evaporation and recent approaches for solution-based processing. The specific properties of the resulting materials and their role as functional layers in organic devices are discussed.

Transition Metal Oxides for Organic Electronics: Energetics, Device Physics and Applications

In order to attain low drive voltage and high power conversion efficiency in tandem OLEDs, the mechanism for carrier generation/separation at the intermediate connecting parts, which are interposed between emission units, has been examined, and a new intermediate connector has been proposed. Voltage increase due to the provision of the new intermediate connector is minimized, and marked decrease in drive voltage of the tandem OLEDs has been attained.

60.2: Intermediate Connector with Suppressed Voltage Loss for White Tandem OLEDs

Conducting polymers, [ 2–4 ] metal inks, [ 5 ] nanoparticulate metal oxides, [ 6 ] carbon nanotubes, [ 7–9 ] and graphene [ 10–12 ] have been investigated as potential alternatives to brittle indium tin oxide (ITO), but none can yet compete in terms of transparency and sheet resistance. Thin meshes of silver nanowires (AgNWs) [ 13–18 ] have recently emerged as promising electrodes due to their ability to provide transmittances greater than 85% at sheet resistances less than 20 Ω sq − 1 . [ 13 , 14 ] Their application to printed electronics, however, is challenging due to a highly non-uniform topography, which can cause shorting through other layers. This is especially problematic for devices using AgNWs as the lower (substrate-facing) electrode since the mesh presents an extremely rough base layer on which to build the device, leading to signifi cant interelectrode shorting. This in turn leads to low shunt resistances, high dark currents, and poor device effi ciencies. For instance, Peumanns and co-workers reported vacuum-deposited organic solar cells (OSCs) on AgNW-coated glass with low shunt resistances of less than 1 k Ω cm 2 and power conversion effi ciencies (PCEs) less than 0.5%. [ 13 ] They subsequently reported polythiophene/ fullerene OSCs with PCEs of 2.5%, [ 16 , 17 ] using the AgNWs in a top-electrode confi guration where their rough morphology is less detrimental to other layers. However to achieve these effi ciencies they fi rst had to pulse the devices at 10 V to burn-out localized shorts with potentially adverse implications for device lifetimes, suggesting a need for alternative device architectures that better suppress shunt formation. In practice most organic devices utilize a transparent substrate through which light passes, and hence they require a transparent lower electrode. To address this need Zeng et al. embedded AgNWs in a thick fi lm of polyvinyl alcohol, ensuring the exposed nanowires sat fl ush with the top of the fi lm and so provided a planar surface on which to deposit further layers. [ 18 ]

Efficient Organic Solar Cells with Solution-Processed Silver Nanowire Electrodes

The authors report a promising metal oxide-doped hole transporting layer (HTL) of rhenium oxide (ReO3)-doped N,N′-diphenyl-N,N′-bis (1,1′-biphenyl)-4,4′-diamine (NPB). The tris(8-hydroxyquinoline) aluminum-based organic light-emitting diodes with ReO3-doped NPB HTL exhibit driving voltage of 5.2–5.4V and power efficiency of 2.2–2.3lm∕W at 20mA∕cm2, which is significantly improved compared to those (7.1V and 2.0lm∕W, respectively) obtained from the devices with undoped NPB. Furthermore, the device with ReO3-doped NPB layer reveals the prolonged lifetime than that with undoped NPB. Details of ReO3 doping effects are described based on the UV-Vis absorption spectra and characteristics of hole-only devices.

https://s-space.snu.ac.kr/bitstream/10371/7016/1/ApplPhysLett_91_011113.pdf

Low driving voltage and high stability organic light-emitting diodes with rhenium oxide-doped hole transporting layer

We investigated the effectiveness of p-dopants to generate holes in a hole transporting material by comparing the absorption in visible-near-infrared and infrared regions and current density-voltage characteristics. CuI, MoO3, and ReO3 having different work functions were doped in a hole transporting organic material, 4,4′,4″-tris(N-(2-naphthyl)-N-phenylamino)-triphenylamine (2TNATA). Formation of charge transfer (CT) complexes increases linearly with increasing doping concentration for all the dopants. Dopants with higher work function (ReO3>MoO3>CuI) are more effective in the formation of CT complexes and in the generation of the charges in the doped films.

/pdf/effectiveness-of-p-dopants-in-an-organic-hole-transporting-5b0fiqtnbc.pdf

Effectiveness of p-dopants in an organic hole transporting material

High quality interconnection units (ICUs) with a high transparency and superior charge generating capability for tandem organic light-emitting diodes (OLEDs) are developed. The ICUs of rubidium carbonate-doped 4,7-diphenyl-1,10-phenanthroline/rhenium oxide (ReO3)-doped N,N′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine layers with or without an additional ReO3 interlayer produce high transmittance (88%–92% at 420–700nm) and spontaneous internal charge generation properties. A very high efficiency of ∼129cd∕A has been demonstrated from only two stacked green p-i-n OLEDs by employing the developed ICUs. The relationship between the device efficiency and internal charge generation within the ICUs is further described by means of the capacitance measurements.

/pdf/highly-efficient-tandem-p-i-n-organic-light-emitting-diodes-69ln3lydz3.pdf

Dong-Seok Leem

Papers

Efficient Organic Solar Cells with Solution-Processed Silver Nanowire Electrodes

Low driving voltage and high stability organic light-emitting diodes with rhenium oxide-doped hole transporting layer

Effectiveness of p-dopants in an organic hole transporting material

Highly efficient tandem p-i-n organic light-emitting diodes adopting a low temperature evaporated rhenium oxide interconnecting layer

Investigation of a Conjugated Polyelectrolyte Interlayer for Inverted Polymer:Fullerene Solar Cells