Showing papers on "Indium tin oxide published in 2007"

Phosphonic Acid-Modified Barium Titanate Polymer Nanocomposites with High Permittivity and Dielectric Strength

Abstract: Materials with high dielectric permittivity are important in electronic components such as capacitors, gate dielectrics, memories, and power-storage devices. Conventional highpermittivity materials such as barium titanate (BT) can be processed into thin films by using chemical solution deposition yielding a relative permittivity (er) of about 2500 and relatively low dielectric loss but require high-temperature sintering, which is not compatible with many substrate materials. Polymer-based dielectrics, such as biaxially oriented polypropylene (BOPP), have good processability with high dielectric strengths (∼ 640 V lm) suitable for high-energy-density capacitors, but the storage capacity (ca. 1–1.2 J cm) is limited by the low er (ca. 2.2) of these materials. [6] Various approaches to high-er materials based on nanocomposites containing metal particles or other conductive materials have been pursued. Such nanocomposites have afforded huge er values but the resulting materials are limited by the high-temperature processing required, high dielectric loss, or low dielectric strength. Polymer/ceramic nanocomposites in which high-er metal oxide nanoparticles such as BT and lead magnesium niobate–lead titanate (PMN–PT) are incorporated into a polymer host are of significant current interest. The combination of high-er nanoparticles with high-dielectric-strength polymer hosts offers the potential to obtain processable highperformance dielectric materials. Simple solution processing of BT particles in a polymer host generally results in poor film quality and inhomogeneities, which are mainly caused by agglomeration of the nanoparticles. Addition of surfactants, such as phosphate esters and oligomers thereof, can improve the dispersion of BT nanoparticles in host polymers and consequently the overall nanocomposite film quality. However, in such systems, residual free surfactant can lead to high leakage current and dielectric loss. Thus, approaches to bind surface modifiers to BT nanoparticles via robust chemical bonds are highly desirable. Ramesh et al. have reported on the use of trialkoxysilane surface modifiers for the dispersion of BT nanoparticles in epoxy polymer hosts resulting in nanocomposites with reasonably high er, up to 45. [12] With the objective of identifying ligands that can form stable bonds to a BT surface through coordination or condensation, we have investigated a series of different ligand functionalities. In this Communication, we report that phosphonic acid ligands effect robust surface modification of BT and related nanoparticles and that the use of particles modified with suitable phosphonic acid ligands leads to well-dispersed BT nanocomposite films with high er and high dielectric strength. We have investigated the binding of a variety of ligands to the surface of BT nanoparticles, as the stability of the binding on the surface is vital to effective surface modification. We examined the following set of ligands, each bearing an aliphatic octyl chain with a different terminal binding group: C8H17-X, where X = PO(OH)2 (OPA), SO2ONa (OSA), Si(OCH3)3 (OTMOS), and CO2H (OCA). Trialkoxysilanes are widely used surface modifiers for silicate, indium tin oxide, and other metal oxide surfaces. Phosphonic acids have been reported to modify TiO2, ZrO2, and indium tin oxide surfaces and are thought to couple to the surface of metal oxides either by heterocondensation with surface hydroxyl groups or coordination to metal ions on the surface. Carboxylic acid and sulfonic acid groups may also bind to the surface in a similar manner. A sample of each ligand was mixed with BT nanoparticles (30–50 nm, 0.5 mmol ligand/ g BT) in an ethanol/water solution and stirred at 80 °C, followed by extensive washing with ethanol or water and centrifugation to remove excess and/or physisorbed ligand. The treated BT nanoparticles were dried and characterized by using Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). Figure 1a shows a comparison of FTIR spectra in the C–H stretching region for the BT nanoparticles treated with the ligands described above, followed by washing. These results C O M M U N IC A IO N

Analysis of the failure mechanism for a stable organic photovoltaic during 10 000 h of testing

Abstract: The degradation and failure mechanisms of a stable photovoltaic device comprising a bilayer heterojunction formed between poly(3-carboxythiophene-2,5-diyl-co-thiophene-2,5-diyl) (P3CT) and Buckminsterfullerene (C 60 ) sandwiched between indium tin oxide (ITO) and aluminium (Al) electrodes were elucidated by the time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis in conjunction with isotopic labelling using 18 O 2 after a total testing time of 13 000 h. This experiment allowed us to understand the chemistry that takes place in three dimensions during degradation and failure of the device under accelerated testing conditions. The cell was subjected to continuous illumination with an incident light intensity of 1000 Wm -2 (AM1-5) at 72±2°C under a vacuum of <10 -6 mBar. During the illumination period, IV-curves were recorded at regular intervals and the short circuit current of the device was monitored every 10s for 10 760 h. The total illumination time was 12 200 h. During this period of time, the device performance degraded and the device was finally left in the dark at 25°C in an atmosphere where the oxygen had been replaced with the isotope 18 O 2 . After 800 h in this atmosphere in the dark, the final IV-curves in the dark and under illumination were recorded. The main purpose of this work was the analysis using TOF-SIMS imaging and depth profiling of the degraded cell. The combined analyses correspond to the three-dimensional chemical imaging of the device showing specifically where the oxygen had reacted during exposure. Several general findings were made that are applicable to similar devices. It was found that the oxygen diffuses into the device through the Al electrode in between the Al grains and through microscopic holes in the Al electrode. Once inside the device the oxygen diffuses in the lateral and vertical plane until the counter electrode is reached. C 60 was found to be susceptible to the incorporation of 18 O but P3CT was not under the conditions in question. The other prominent degradation pathway was found to be the diffusion of electrode materials into the device. Both electrode materials diffuse through the entire device to the counter electrode.

Nanoimprinted semitransparent metal electrodes and their application in organic light-emitting diodes

Abstract: Organic light-emitting diodes (OLEDs) are promising for full-color, full-motion, flat panel display applications because they offer several advantageous features, for example, ease of fabrication, low costs, light weight, bright self-emission, a wide viewing angle, and the possibility of flexible displays. The basic OLED structure consists of a number of organic semiconductor layers sandwiched between a cathode and an anode. For efficient electron injection into the organic layers, low-work-function materials are required for the cathode. A very thin LiF layer with a thick Al capping is widely used for this purpose. For the anode, indium tin oxide (ITO) is the predominant choice because it offers transparency in the visible range of the electromagnetic spectrum as well as electrical conductivity. However, several aspects of ITO are far from optimal for high-performance OLEDs. It is known that the migration of indium and oxygen from ITO into organic semiconductors during OLED operation causes device degradation. The electrical properties of ITO greatly depend on the film preparation. The rough surface of the deposited ITO film and the work function of ITO, ca. 4.7 eV, limit the efficiency of the hole injection. The typical sheet resistance of a 100 nm thick ITO layer, 20–80 X/ , is still high, which causes a voltage drop along the addressing line, thus limiting the operation of a large-area passive matrix OLED array. Moreover, the cost of ITO has escalated in recent years because of the jump in price of the element indium. Several alternative materials, for example, TiN, Al-doped ZnO, and fluorine tin oxide, have been investigated as anode materials instead of ITO; however, none are optimal as anode in OLEDs because they have either a lower work function or a lower conductivity than ITO. Other transparent conducting oxides, such as Ga–In–Sn–O (GITO), Zn–In–Sn–O (ZITO), Ga–In–O (GIO), and Zn–In–O (ZIO), that have a higher work function and a similar electrical conductivity when compared to ITO have also been examined as OLED anode materials. However, they are potentially problematic because they also contain the element indium that i) may diffuse into the organic layer in the OLED; and ii) has a high price, making these electrodes expensive. Besides these materials several metals with a high work function, such as Au, Ni, and Pt, have been investigated as anodes for OLEDs. In these cases the metal was used to modify the surface of the ITO electrode, or as an anode for top-emitting devices. A surface-modified thin Ag film has been used as a semitransparent electrode instead of ITO, but its transparency was low. Recently, carbon nanotube films have been investigated as transparent, conductive electrodes, but they have a high sheet resistance that may limit the device performance. In this Communication, we report semitransparent metal electrodes fabricated by nanoimprint lithography (NIL), and evaluate their potential as OLED anodes. NIL, an emerging lithographic technique, is well-suited to the area of organic electronics, which requires low-cost and high-throughput fabrication at high resolution. The fabricated semitransparent metal electrode offers several advantages over ITO for OLED applications. First, several problems associated with ITO can be eliminated, such as device degradation by indium diffusion and high costs. Second, efficient hole injection into the organic semiconductor can be realized by choosing metals with a high work function, such as Au or Pt. Third, a semitransparent metal electrode is potentially suitable for topemitting devices and tandem structures. Last, but not least, the output efficiency of the OLED can be enhanced by preventing waveguiding in the ITO layer, which occurs as a result of its high refractive index and is one of the limitations to the external efficiency of OLEDs, and by forming a two-dimensional (2D) hole array with proper periodicity. We demonstrate here that a unique property of such an electrode is that its optical transparency and the electrical conductivity can be tuned separately by changing the aperture ratio and the metal thickness, thereby making it possible to tailor the structures for different applications. To our knowledge, a nanoimprinted semitransparent metal electrode has not been reported before. The semitransparent metal electrodes are in the form of a nanometer-scale periodically perforated dense metal mesh on glass. Two design considerations led to such structures: i) the line width of the metal mesh was designed to be subwavelength, to provide sufficient transparency and to minimize light scattering; and ii) the period of the mesh was chosen to be sub-micrometer to ensure the uniformity of the current injection into the organic semiconductors. Such large-area dense nanostructures can be fabricated by NIL, which is ideal for this application because of its inherently high resolution C O M M U N IC A IO N

Amorphous gallium indium zinc oxide thin film transistors: Sensitive to oxygen molecules

Abstract: In this study, the authors report characteristic of indium gallium zinc oxides (GIZOs) which is strongly associated with the film surface. In ambient air, turn-on voltage of GIZO thin film transistors is approximately −7V. However, at the pressure of 8×10−6Torr, the turn-on voltage dramatically shifts to nearly −47V of the negative gate bias direction. When the oxygen is introduced in the chamber, the turn-on voltage returns to the normal value, that of air. It is believed that the adsorbed oxygen forms depletion layer below the surface, resulting in Von shifts. The carrier concentration of the channel varies from 1×1019to1×1020cm−3 due to oxygen adsorption.

Improved performances of organic light-emitting diodes with metal oxide as anode buffer

Abstract: We demonstrate extremely stable and highly efficient organic light-emitting diodes (OLEDs) based on molybdenum oxide (MoO3) as a buffer layer on indium tin oxide (ITO). The significant features of MoO3 as a buffer layer are that the OLEDs show low operational voltage, high electroluminescence (EL) efficiency and good stability in a wide range of MoO3 thickness. A green OLED with structure of ITO∕MoO3∕N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidene (NPB)∕NPB: tris(8-hydroxyquinoline) aluminum (Alq3):10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H, 5H, 11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T)∕Alq3∕LiF∕Al shows a long lifetime of over 50000h at 100cd∕m2 initial luminance, and the power efficiency reaches 15lm∕W. The turn-on voltage is 2.4V, and the operational voltage at 1000cd∕m2 luminance is only 6.9V. The significant enhancement of the EL performance is attributed to the improvement of hole injection and interface stability at anode.

Formation of Ohmic hole injection by inserting an ultrathin layer of molybdenum trioxide between indium tin oxide and organic hole-transporting layers

Abstract: Current density–voltage (J-V) characteristics of hole-only devices using indium tin oxide (ITO) anode and N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) layers were measured with various thicknesses of a molybdenum trioxide (MoO3) buffer layer inserted between ITO and α-NPD. The device with a 0.75-nm-thick MoO3 layer forms Ohmic hole injection at the ITO∕MoO3∕α-NPD interfaces and J-V characteristics of this device are controlled by a space-charge-limited current. Results of X-ray photoelectron and ultraviolet/visible/near-infrared absorption studies revealed that this Ohmic hole injection is attributable to an electron transfer from ITO and α-NPD to MoO3.

Efficient Charge Collection with ZnO Nanorod Array in Hybrid Photovoltaic Devices

Abstract: Photovoltaic performance of the hybrid devices consisting of polymer/fullerene/ZnO nanorod array was studied The dependence of the photovoltaic performance on the ZnO nanorod length and the organic layer thickness was investigated, and it is concluded that the ZnO nanorod array plays an important role in collecting photogenerated electrons and acts as a conducting path to the indium tin oxide electrode Fill factor of the devices increased from 38% to 50% when the array of the ZnO nanorods was introduced, which directly contributed to the improvement of the power conversion efficiencies up to 27% As the peak absorption of the device reaches >97% in a transmitting geometry, the results shown here give us insights toward designing the devices with efficient utilization of the incident light

Electrode Grids for ITO Free Organic Photovoltaic Devices

Abstract: Organic materials, such as conjugated polymers, have emerged as a promising alternative for the production of inexpensive and flexible photovoltaic cells. As conjugated polymers are soluble, liquid based printing techniques enable production on large scale to a price much lower than that for inorganic based solar cells. Present day state of the art conjugated polymer photovoltaic cells are comprised by blends of a semiconducting polymer and a soluble derivative of fullerene molecules. Such bulk heterojunction solar cells now show power conversion efficiencies of up to 4-6%. The quantum efficiency of thin film organic solar cells is however still limited by several processes, of which the most prominent limitations are the comparatively low mobility and the high level of charge recombination. Hence organic cells do not yet perform as well as their more expensive inorganic counterparts. In order to overcome this present drawback of conjugated polymer photovoltaics, efforts are continuously devoted to developing materials or devices with increased absorption or with better charge carrier transporting properties. The latter can be facilitated by increasing the mobility of the pure material or by introducing beneficial morphology to prevent carrier recombination. Minimizing the active layer film thickness is an alternative route to collect more of the generated free charge carriers. However, a minimum film thickness is always required for sufficient photon absorption. A further limitation for low cost large scale production has been the dependence on expensive transparent electrodes such as indium tin oxide. The development of cheaper electrodes compatible with fast processing is therefore of high importance. The primary aim of this work has been to increase the absorption in solar cells made from thin films of organic materials. Device construction, deploying new geometries, and evaluation of different methods to provide for light trapping and photon recycling have been strived for. Different routes to construct and incorporate light trapping structures that enable higher photon absorption in a thinner film are presented. By recycling the reflected photons and enhancing the optical path length within a thinner cell, the absorption rate, as well as the collection of more charge carriers, is provided for. Attempts have been performed by utilizing a range of different structures with feature sizes ranging from nanometers up to centimeters. Surface plasmons, Lambertian scatterers, micro lenses, tandem cells as well as larger folded cell structures have been evaluated. Naturally, some of these methods have turned out to be more successful than others. From this work it can nevertheless be concluded that proper light trapping, in thin films of organic materials for photovoltaic energy conversion, is a technique capable of improving the cell performance. In addition to the study of light trapping, two new alternative electrodes for polymer photovoltaic devices are suggested and evaluated.

Highly efficient simplified organic light emitting diodes

Abstract: The authors report on highly efficient organic light emitting diodes (OLEDs) consisting of only two organic layers. The key to the simplification is the direct injection of holes into the wide band gap hole transport material 4,4′,4″-tris(N-carbazolyl)-triphenyl amine (highest occupied molecular orbital is 5.9eV) through an indium tin oxide/tungsten oxide (WO3) anode. Kelvin probe analysis has revealed an extremely high work function of 6.4eV for WO3. The efficiencies of the simplified OLEDs exceed 40lm∕W and 45cd∕A at a brightness of 100cd∕m2, unsurpassed by other comparably simple OLED devices. Therefore, our OLED architecture demonstrates highly efficient, yet easy to fabricate devices.

Improved conductivity of transparent single-wall carbon nanotube thin films via stable postdeposition functionalization

Abstract: A simple postdeposition method for improving the conductivity of transparent and conducting single-wall carbon nanotube (SWNT) thin films via exposure to nitric acid and thionyl chloride is reported. A systematic study on a range of films of variable density and from different commercial sources of SWNTs is performed. The functionalized films possess sheet resistances as low as that of indium tin oxide (ITO) (∼30Ω∕◻) albeit at lower transmittance (∼50%). At 80±5% transmittance, the functionalized films have resistance values ranging from 150to300Ω∕◻. The SWNT films, however, are more flexible than ITO. The stability of the functionalized films upon annealing and processing in solvents (water, methanol, and chloroform) is also reported.

Control of the electrode work function and active layer morphology via surface modification of indium tin oxide for high efficiency organic photovoltaics

Abstract: Indium tin oxide (ITO) substrates modified with self-assembled monolayers (SAMs) were used to control the anode work function and active layer morphology of organic solar cells based on poly(3-hexylthiophene)/[6:6]-phenyl-C61 butyric acid methyl ester heterojunctions. By using SAMs with the terminal groups –NH2, –CH3, and –CF3, the authors were able to control the hole injection barrier of the ITO closer to the highest occupied molecular orbital level of active layer and surface energy of the ITO substrate. A solar cell device with CF3 SAM treated ITO was found to exhibit high efficiency performance, about 3.15%.

Efficient polymer solar cells fabricated by simple brush painting

Abstract: Since the report of a molecular thin-film organic solar cell (OSC) by Tang, organic materials have increasingly become attractive candidates for the fabrication of cost-efficient and flexible photovoltaic cells. In particular, polymer bulkheterojunction (BHJ) solar cells based on interpenetrating networks of an electron donor and an acceptor, with a largearea donor and acceptor interface, resulting in an efficient photo-induced charge separation, have gained considerable interest. Despite of their relatively low efficiency in comparison to conventional inorganic solar cells, the potential of roll-to-roll processing on low-cost and flexible substrates makes polymer solar cells (PSCs) so attractive as a cost-effective solution to the energy problems we are facing today. Among the various BHJ systems, poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61butyric acid methyl ester (PCBM) networks produced by spin-coating a blend combined with a preor post-heat treatment to improve the degree of ordering of P3HT have shown the highest efficiencies up to ca. 4–5 % under 80 or 100 mW cm illumination under AM 1.5 G condition. Because the electrical and optical properties of conjugated polymers are strongly dependent on the structural order of polymers, the processing methods and conditions, which determine the degree of organization of polymers, have a critical influence on the performance of electrical and optoelectrical devices based on these polymers. In addition, considering efficiencies of ca. 5 %, the development of novel solution processes that are compatible with low-cost mass production is one of the crucial requirements for practical device applications. Here, we report on novel solution-processed high-efficiency polymer solar cells based on a blend of P3HT and PCBM, resulting from improved organization of the P3HT. By directly brush painting a blend of P3HT and PCBM on appropriately temperature-controlled substrates, enhanced ordering of the polymers, induced by the shear stress in the direction parallel to the brushing direction, was achieved. This highly ordered active layer facilitates charge transport separated at the interface of the P3HT and PCBM, leading to an increased efficiency, in particularly an improved fill factor. In addition, this novel solution process can be considered a promising method for the fabrication of flexible and large-area polymer solar cells based on high-throughput roll-to-roll manufacturing, which would make the realization of low-cost PSCs possible. First, two types of devices were fabricated by conventional spin-coating and brush painting, respectively, without any preor post-heat treatment, which are usually performed to stabilize a nanoscale interpenetrating network with a crystalline order, resulting in an increase in overall conversion efficiency. Figure 1 shows the schematic of the brushing method and the resulting I–V curves for the two types of devices. The brush painting was performed on a poly(3,4-ethylenedioxythiophene) (PEDOT):poly(styrene sulfonate) (PSS)-coated indium tin oxide (ITO) substrate on a hot plate with a temperature of 50 °C. A general paintbrush made of nylon fibrils was used and the active layer was coated with a speed of ca. 1.5 cm s. It took ca. 2 s to prepare a complete film on the ITO substrate with a size of 1.5 cm × 1.5 cm by brush painting twice. During the brush painting process, an appropriate temperature was necessary to make a smooth and uniform active layer with a high degree of ordering, which is related to the evaporation rate of the solvents. In our case chlorobenzene was used, for which good-quality films could not be obtained when the brush painting was carried out below 50 °C because of too slow evaporation of the solvent at low temperatures. To prepare active layers with the same thickness, the blend was spin-coated at room temperature on the PEDOT:PSScoated ITO substrate at 2000 rpm and the thickness was determined to be ca. 90 nm by means of a surface profiler (Kosaka ET-3000i). The surface morphologies determined by atomic force microscopy (AFM) for the surfaces produced by the brushing technique (with a rms roughness of ca. 0.91 nm) were similar to that of a conventional spin-coated active layer (not shown here). As shown in Figure 1b, the performance was improved when the active layer was prepared by the brush-painting process. In the case of a spin-coated device, a poor performance was observed with VOC (opencircuit voltage) = 0.6 V, ISC (short-circuit current density) = 3.59 mA cm, FF (fill factor) = 32.5 %, and ge (power conversion efficiency) = 0.7 %, which is similar to previous C O M M U N IC A TI O N

High-Performance, Spin-Coated Zinc Tin Oxide Thin-Film Transistors

Abstract: We have developed a general and low-cost, solution-based process that is suitable for the deposition of transparent conducting oxides through spin-coating or inkjet printing under ambient conditions. Highly transparent (-95% in the visible portion) zinc tin oxide semiconducting thin films were deposited by spin coating. The deposited films were found to be smooth and uniform with an amorphous structure. Enhancement-mode metal-insulator-semiconductor field-effect transistors were fabricated showing a field-effect mobility (μ FE ) as high as 16 cm 2 /V s, a turn-on voltage of 2 V, a current on-to-off ratio greater than 10 5 , and a high on-current of 2.25 mA.

Photocatalytic degradation characteristics of different organic compounds at TiO2 nanoporous film electrodes with mixed anatase/ rutile phases.

Abstract: Nanoporous TiO2 film electrodes with a mixed anatase/rutile phase were prepared by dip-coating TiO2 nanoparticle colloid onto Indium Tin Oxide (ITO) conducting glass substrates and a subsequent calcination process at 700 °C for 16 h. The photocatalytic oxidation of a wide range of organic compounds has been studied using the photoelectrochemical method under the conditions that the photohole capturing step controls the overall photocatalytic processes. The characteristics of the mixed anatase/rutile phase TiO2 film electrodes were compared with pure anatase phase TiO2 film electrodes to identify the key differences between them. The results revealed that different organic compounds, despite their difference in chemical entities, can be stoichiometrically mineralized at the mixed-phase TiO2 electrode under diffusion-controlled conditions, which is in great contrast to the situation at the pure anatase phase TiO2 electrode. The exceptional ability of the mixed-phase TiO2 electrodes for mineralization of org...

Gallium-doped zinc oxide films as transparent electrodes for organic solar cell applications

Abstract: We report microstructural characteristics and properties of gallium-doped ZnO films deposited on glass by pulsed laser deposition. The Zn0.95Ga0.05O film deposited at 200 °C and 1×10−3 Torr showed predominant ⟨0001⟩ orientation with a metallic behavior and a resistivity of 2×10−4 Ω cm at room temperature. Low resistivity of the ZnGaO films has been explained in terms of optimal combination of carrier concentration and minimized scattering, and is correlated with the microstructure and the deposition parameters. Power conversion efficiency comparable to indium tin oxide-based devices (1.25±0.05%) is achieved on a Zn0.95Ga0.05O∕Cu-phthalocyanine∕C60 double-heterojunction solar cell.

Nonvolatile polymer memory device based on bistable electrical switching in a thin film of poly(N-vinylcarbazole) with covalently bonded C60.

Abstract: A functional polymer (PVK-C60), containing carbazole moieties (electron donors) and fullerene moieties (electron-acceptors) in a molar ratio of about 100:1, was synthesized via covalent tethering of C60 to poly(N-vinylcarbazole) (PVK). The molecular structure and composition of PVK-C60 were characterized by FTIR, Raman, and UV-vis absorption spectroscopy, gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CyV). The C60-modified PVK exhibited an enhanced glass-transition temperature (Tg = 226 degrees C) and good solubility in organic solvents such as toluene, tetrahydrofuran, chloroform, and N,N-dimethylformamide (DMF). It could be cast into transparent films from solutions. For a thin film of PVK-C60 sandwiched between an indium tin oxide (ITO) electrode and an Al electrode (ITO/PVK-C60/Al), the device behaved as nonvolatile flash (rewritable) memory with accessible electronic states that could be written, read, and erased. The polymer memory exhibited an ON/OFF current ratio of more than 105 and write/erase voltages around -2.8 V/+3.0 V. Both the ON and OFF states were stable under a constant voltage stress of -1 V for 12 h and survived up to 108 read cycles at -1 V under ambient conditions.

Transparent ZnO thin film transistor fabricated by sol-gel and chemical bath deposition combination method

Abstract: Top-gate thin film transistors with n-type ZnO active channel were performed under 230°C. Especially, ZnO film was deposited by a combined method of sol-gel and chemical bath deposition without any preactivation for film growth. Silicon nitride and indium tin oxide were used as the gate insulator and the conducting electrodes (source, drain, and gate). These transistors were highly transparent in the visible spectrum, with transmittance as high as 75% to approximately 85% at wavelength from 500to700nm. The optimum device has field-effect mobility of 0.67cm2∕Vs and an on-off ratio more than 107.

Fabrication of highly conductive Ti1- xNbxO2 polycrystalline films on glass substrates via crystallization of amorphous phase grown by pulsed laser deposition

Abstract: Nb-doped anatase TiO2 [Ti0.94Nb0.06O2 (TNO)] films with high electrical conductivity and transparency were fabricated on nonalkali glass using pulsed laser deposition and subsequent annealing in a H2 atmosphere. The amorphous films as deposited on unheated substrates were found to crystallize, forming polycrystalline films at around 350°C. The films annealed at 500°C showed resistivity down to 4.6×10−4Ωcm at room temperature and optical transmittance of 60%–80% in the visible region, which are comparable to those of epitaxial films. These results indicate that TNO films have the potential to be practical transparent conducting oxides that could replace indium tin oxide.

Material design of hole transport materials capable of thick-film formation in organic light emitting diodes

Abstract: In this study, the authors show an empirical guideline for designing hole transport materials (HTMs) that suppress rises in driving voltage even with a few hundred nanometer thick film in the organic light emitting diodes (OLEDs). In a device structure of indium tin oxide (110nm)/hole transport layer (HTL) (Xnm)∕4,4′-N,N′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (10nm)/tris-(8-hydroxyquinoline)aluminum (Alq3) (50nm)∕MgAg (100nm)∕Ag (10nm), the authors compared electroluminescence characteristics of the OLEDs having a thin-film HTL (X=50nm) and a thick-film HTL (X=300nm) using 13 kinds of HTMs. They observed a closed correlation between suppression of the driving voltage and the HTMs’ thermal characteristics. Highly thermally stable HTMs resulted in a small increase in the driving voltage.

Room temperature pulsed laser deposited indium gallium zinc oxide channel based transparent thin film transistors

Abstract: Indium gallium zinc oxide deposited by pulsed laser deposition at room temperature was used as a channel layer to fabricate transparent thin film transistors with good electrical characteristics: field effect mobility of 11cm2V−1s−1 and subthreshold voltage swing of 0.20V∕decade. By varying the oxygen partial pressure during deposition the conductivity of the channel was controlled to give a low off-current of ∼10pA and a drain current on/off ratio of ∼5×107. Changing the channel layer thickness was a viable way to vary the threshold voltage. The effect of the gate dielectric on the electrical behavior was also explored.

Transparent metallic Sb-doped SnO2 nanowires

Abstract: The authors report the growth and characterization of single-crystalline, degenerately Sb-doped SnO2 (SnO2:Sb) nanowires The in situ doped SnO2:Sb nanowires are transparent conductors with resistivities down to 41×10−4Ωcm and failure-current densities up to 21×107A∕cm2 High carrier concentrations (>1020cm−3) and minimal environmental effects were also observed and attributed to effective Sb doping The SnO2:Sb nanowires can be obtained at large quantities using a low-cost vapor transport method and may provide a suitable alternative to indium tin oxide as transparent conducting oxide materials Field emission devices with SnO2:Sb nanowire cathodes and anodes exhibited an ultralow turn-on voltage of 2V

Self-Cleaning Transparent Dust Shields for Protecting Solar Panels and Other Devices

Abstract: The development of transparent flexible dust shields using both single- and three-phase electrodynamic shields is reported here for possible application on Mars and Earth to minimize obscuration of solar panels from the deposition of dust. The electrodynamic screens (EDS) are made of transparent plastic sheets, such as polyethylene terephthalate (PET) for its UV radiation resistance, and a set of parallel conducting electrodes made of transparent indium tin oxide (ITO) embedded under a thin transparent film. The basic principle of EDS operation, a simplified mathematical model of particle trajectories, the experimental setup used for testing the screens, and their dust removal efficiencies (DRE) are described. Results of our measurements on dust removal efficiency of EDS as a function of the particle size and electrostatic charge distributions of Mars simulant dust are reported. The results show that the EDS technology has a strong potential for protecting solar panels against dust hazards with DRE higher...

Tuning optical band gap of vertically aligned ZnO nanowire arrays grown by homoepitaxial electrodeposition

Abstract: Vertically aligned ZnO nanowire arrays are grown homoepitaxially on the ZnO seeded indium tin oxide substrate by electrochemical deposition from aqueous solution at low temperature (70°C) without using any template. ZnO nanowires exhibit single crystalline, wurtzite crystal structure determined by transmission electron microscopy and powder x-ray diffraction. The ZnO nanowire arrays show high transmittance in the visible wavelengths. Interestingly, the optical band gap of the ZnO nanowire arrays has been tuned by simply changing zinc salts in the electrodeposition from aqueous solution.

The Effect of Aggregation on the Electrical Conductivity of Spin-Coated Polymer/Carbon Nanotube Composite Films

Abstract: This paper considers the feasibility of replacing indium tin oxide (ITO) with spin-coated, polymer-based composite films that are filled with multiwalled carbon nanotubes (MWNTs). The coating mixture consists of a solvent with low volatility, a dissolved thermoplastic polymer, and MWNTs. The high aspect ratio of MWNTs and their good electrical conductivity enable electrical percolation at very low concentrations, so that films can be prepared that conduct electricity while retaining good optical transparency. Although the MWNTs are driven to aggregate by Van der Waals interactions, the high viscosity of the polymer/solvent solution enables the preparation of metastable, homogeneous dispersions. However, exposing the mixtures to shear leads to aggregation, the magnitude of which depends on the duration of the shear. This effect could be observed directly in spin-coated films using both optical microscopy and conductivity measurements, with aggregation causing a drop in conductivity at high nanotube loading, and more complex non-monotonic behavior at concentrations approaching the percolation threshold.

Surface composition and electrical and electrochemical properties of freshly deposited and acid-etched indium tin oxide electrodes.

Abstract: We compare the near-surface composition and electroactivity of commercial indium tin oxide (ITO) thin films, activated by plasma cleaning or etching with strong haloacids, with ITO films that have been freshly deposited in high vacuum, before and after exposure to the atmosphere or water vapor. Conductive-tip AFM, X-ray photoelectron spectroscopy (XPS), and the electrochemistry of probe molecules in solution were used to compare the relative degrees of electroactivity and the near-surface composition of these materials. Brief etching of commercial ITO samples with concentrated HCl or HI significantly enhances the electrical activity of these oxides as revealed by C-AFM. XPS was used to compare the composition of these activated surfaces, focusing on the intrinsically asymmetric O 1s line shape. Energy-loss processes associated with photoemission from the tin-doped, oxygen-deficient oxides complicate the interpretation of the O 1s spectra. O 1s spectra from the stoichiometric indium oxide lattice are accom...