Showing papers on "Indium tin oxide published in 2005"

High-Conductivity Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) Film and Its Application in Polymer Optoelectronic Devices†

Abstract: The conductivity of a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film can be enhanced by more than two orders of magnitude by adding a compound with two or more polar groups, such as ethylene glycol, meso-erythritol (1,2,3,4-tetrahydroxybutane), or 2-nitroenthanol, to an aqueous solution of PEDOT:PSS. The mechanism for this conductivity enhancement is studied, and a new mechanism proposed. Raman spectroscopy indicates an effect of the liquid additive on the chemical structure of the PEDOT chains, which suggests a conformational change of PEDOT chains in the film. Both coil and linear conformations or an expanded-coil conformation of the PEDOT chains may be present in the untreated PEDOT:PSS film, and the linear or expanded-coil conformations may become dominant in the treated PEDOT:PSS film. This conformational change results in the enhancement of charge-carrier mobility in the film and leads to an enhanced conductivity. The high-conductivity PEDOT:PSS film is ideal as an electrode for polymer optoelectronic devices. Polymer light-emitting diodes and photovoltaic cells fabricated using such high-conductivity PEDOT:PSS films as the anode exhibit a high performance, close to that obtained using indium tin oxide as the anode.

Conducting and transparent single-wall carbon nanotube electrodes for polymer-fullerene solar cells

Abstract: We describe the use of single-wall carbon nanotube (SWNT) thin films as transparent and conducting electrodes for hole collection in poly(hexyl)thiophene-[6-6]phenyl-C61-butyric acid methyl ester (P3HT-PCBM) organic photovoltaics. We report a power conversion efficiency of 1%, with a fill factor of 0.3 and a short-circuit current of 6.5mA∕cm2 under 100mW∕cm2 polychromatic white light illumination measured in air. These values are comparatively higher than reference cells of similar thickness made on indium tin oxide (ITO) glass substrates. This is attributed to the three-dimensional nature of the interface between the SWNTs and the P3HT-PCBM nanocomposite. Our results indicate that solution processed SWNT thin films are a viable alternative to ITO for photovoltaic devices, eliminating an expensive vacuum deposition step in the fabrication of organic solar cells.

High-performance hole-transport layers for polymer light-emitting diodes. Implementation of organosiloxane cross-linking chemistry in polymeric electroluminescent devices.

Abstract: This contribution describes an organosiloxane cross-linking approach to robust, efficient, adherent hole-transport layers (HTLs) for polymer light-emitting diodes (PLEDs). An example is 4,4‘-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPDSi2), which combines the hole-transporting efficiency of N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1-biphenyl)-4,4-diamine) (TPD, prototypical small-molecule HTL material) and the strong cross-linking/densification tendencies of organosilanol groups. Covalent chemical bonding of TPDSi2 to PLED anodes (e.g., indium tin oxide, ITO) and its self-cross-linking enable fabrication of three generations of insoluble PLED HTLs: (1) self-assembled monolayers (SAMs) of TPDSi2 on ITO; (2) cross-linked blend networks consisting of TPDSi2 + a hole transporting polymer (e.g., poly(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl))diphenylamine), TFB) on ITO; (3) TPDSi2 + TFB blends on ITO substrates precoated with a conventional PLED HTL, poly(3,4-ethylenedioxythiophene)-poly(styre...

Selective Functionalization of In2O3 Nanowire Mat Devices for Biosensing Applications

Abstract: A strategy to covalently attach biological molecules to the electrochemically active surface of indium oxide nanowire (In2O3 NW) mat devices is presented. A self-assembled monolayer (SAM) of 4-(1,4-dihydroxybenzene)butyl phosphonic acid (HQ-PA) was generated on an indium tin oxide (ITO)-coated glass and In2O3 NWs surface. The chemical steps required for surface derivatization were optimized on an ITO surface prior to modifying the In2O3 NWs. The hydroquinone group contained in the HQ-PA SAM was electrochemically oxidized to quinone (Q-PA) at +330 mV. The monolayer of Q-PA was allowed to react with a thiol-terminated DNA. The DNA was paired to its complementary strand tagged with a fluorescence dye. Attachment of DNA was verified using fluorescence microscopy. A device was subsequently prepared on a SiO2-supported mat of In2O3 NWs by depositing gold electrodes on the mat surface. The reaction strategy optimized on ITO was applied to this In2O3 NW-based device. Arrays of In2O3 NWs on a single substrate were...

Advanced surface modification of indium tin oxide for improved charge injection in organic devices.

Abstract: A new method is described for surface modification of ITO with an electroactive organic monolayer. This procedure was done to enhance hole injection in an electronic device and involves sequential formation of a monolayer of a π-conjugated organic semiconductor on the indium tin oxide (ITO) surface followed by doping with a strong electron acceptor. The semiconductor monolayer is covalently bound to the ITO, which ensures strong adhesion and interface stability; reduction of the hole injection barrier in these devices is accomplished by formation of a charge-transfer complex by doping within the monolayer. This gives rise to very high current densities in simple single layer devices and double layer light emitting devices compared to those with untreated ITO anodes.

High efficiency visible electroluminescence from silicon nanocrystals embedded in silicon nitride using a transparent doping layer

Abstract: We have fabricated light-emitting diodes with a transparent doping layer on silicon nanocrystals (nc-Si) embeded in silicon nitride matrix formed by plasma-enhanced chemical vapor deposition. Under forward biased condition, orange electroluminescence (EL) with its peak wavelength at about 600 nm was observed at room temperature. The peak position of the EL is very similar to that of the photoluminescence (PL) and the emitted EL intensity is proportional to the current density passing through the device. We suggest that the observed EL is originated from electron-hole pair recombination in nc-Si. By using indium tin oxide and n-type SiC layer combination as a transparent doping layer, we obtained high external quantum efficiency greater than 1.6%.

Self-assembly of active IrO2 colloid catalyst on an ITO electrode for efficient electrochemical water oxidation.

Abstract: Active catalysts for water oxidation to evolve O2 are required for the construction of artificial photosynthetic devices that are expected to be promising energy-providing systems in the future. The citrate-stabilized IrO2 colloid was self-assembled onto an indium tin oxide (ITO) electrode to form a monolayer of the colloidal IrO2 particles when it was dipped in the colloid solution. The self-assembly could be achieved by a chemical interaction between carboxylate groups on the citrate stabilizer and hydroxyl groups on the ITO surface to form ester bonds. Efficient electrocatalysis for water oxidation was demonstrated using the electrode modified by the self-assembled IrO2 colloid to yield the highest turnover frequency ((2.3−2.5) × 104 h-1) of IrO2 in the hitherto-reported catalysts for electrochemical water oxidation.

Electrochemical Tuning of Silver Nanoparticles Fabricated by Nanosphere Lithography

Abstract: An electrochemical method is developed to quantitatively modify and spectroscopically monitor the size and shape of Ag nanotriangles fabricated by nanosphere lithography (NSL) on an indium tin oxide (ITO) electrode surface. AFM and SEM results demonstrate that the preferential order of electrochemical oxidation for a nanotriangle is, surprisingly, bottom edges first, then triangular tips, then out-of-plane height.

GaN-based light-emitting diodes with indium tin oxide texturing window layers using natural lithography

Abstract: There is a significant gap between the internal and external efficiencies of conventional GaN light-emitting diodes (LEDs). The reason for this shortfall is the narrow escape cone for light in high refractive index semiconductors. In this letter, the p-side-up GaN∕sapphire LEDs with surface textured indium tin oxide (ITO) widow layers were investigated using natural lithography with polystyrene spheres as the etching mask. Under optimum etching conditions, the surface roughness of the ITO film can reach 140 nm while the polystyrene sphere on the textured ITO surface is maintained at about 250–300 nm in diameter. The output power of the ITO∕GaN LED with and without surface texturing is 10.9, and 8.5 mW at 20 mA, respectively. The LEDs fabricated using the surface-textured ITO produced an output power that exceeded that of the planar-surface LED by about 28% at 20 mA.

Electromechanical Properties of Transparent Conducting Substrates for Flexible Electronic Displays

Abstract: As opto-electronic devices become flexible, the designing of reliable devices becomes more challenging. In this paper, we focus on the degradation of flexible transparent anodes by mechanical and thermal stresses. Indium tin oxide (ITO)-coated polyethyleneterephthalate (PET) is susceptible to cracking at low strains (<2%), but has excellent electrical and optical characteristics. Conducting polymers, such as polyethylene dioxythiophene doped with polystyrene sulfonate (PEDOT:PSS), have good mechanical properties, but are severely degraded by temperature, and have inferior optical and electronic properties. We have developed a mandrel-bending automated test system to evaluate the degradation of flexible anodes in service, and find that even when the strain is below the virgin cracking threshold, there are measurable changes in ITO resistance. Cyclic loading of ITO-coated PET shows three regimes of resistance increase: 1) an increase in resistance, due to changes in sample dimension until equilibrium width is obtained (50-100 cycles); 2) a gradual linear increase in resistance, possibly due to cracking of ITO; and 3) a catastrophic failure after 50 000 cycles due to severe cracking. For PEDOT:PSS-coated PET, the resistance does not increase significantly with increasing tensile strain, and it is also less susceptible to damage from repeated bending.

Electrochemical growth of two-dimensional gold nanostructures on a thin polypyrrole film modified ITO electrode.

Abstract: Two-dimensional gold nanostructures have been fabricated by electrochemical deposition of gold nanoparticles onto indium tin oxide (ITO) glass substrate modified with thin polypyrrole film. By controlling the electrodeposition conditions, gold nanoparticles with dendritic rod, sheet, flower-like (consisting of staggered nanosheets), and pinecone-like structures were generated. The flower-like gold nanoparticles showed high catalytic activity on electrochemical reduction of oxygen, and its activity was measured to be approximately 25 times that of gold pinecones and 104 times that of gold nanosheets in terms of gold weight. The pinecone-like nanoparticles can form a compact film with nano-/microscale binary structure like a lotus leaf surface. After modification with n-dodecanethiol, the surface showed superhydrophobic properties with a water contact angle of 153.4° and a tilt angle of 4.4° (5 μL droplet).

Symmetric diblock copolymer thin films on rough substrates. Kinetics and structure formation in pure block copolymer thin films

Abstract: The effect of substrate roughness on the orientation of lamellar microdomains of symmetric poly(styrene)-block-poly(methyl methacrylate) [PS-b-PMMA] was investigated. Thin films of three molecular weights of PS-b-PMMA were prepared on organic polyimide and inorganic indium tin oxide substrates whose surfaces were characterized for roughness and surface energy. It was shown, through cross-section transmission electron microscopy (TEM) and dynamic secondary ion mass spectroscopy (dSIMS), that above a critical substrate roughness all three molecular weights of PS-b-PMMA produced a perpendicular lamellar orientation. Using atomic force microscopy (AFM) and PS-b-PMMA thin films on an array of polyimide substrates of varied substrate roughness, a critical substrate roughness was identified, below which a parallel orientation was observed. This behavior was modeled simply and showed that the critical roughness determined by AFM represents an underestimate of the true critical roughness of the substrate. Finally,...

Ta-doped Anatase TiO2 Epitaxial Film as Transparent Conducting Oxide

Abstract: We present electrical transport and optical properties of Ta-doped TiO2 epitaxial thin films with varying Ta concentration grown by the pulsed laser deposition method. The Ti0.95Ta0.05O2 film exhibited a resistivity of 2.5×10-4 Ω cm at room temperature, and an internal transmittance of 95% in the visible light region. These values are comparable to those of a widely used transparent conducting oxide (TCO), indium tin oxide. Furthermore, this new material falls into a new category of TCOs that utilizes d electrons.

Plasma damage-free sputtering of indium tin oxide cathode layers for top-emitting organic light-emitting diodes

Abstract: We report on plasma damage-free sputtering of an indium tin oxide (ITO) cathode layer, which was grown by a mirror shape target sputtering (MSTS) technique, for use in top-emitting organic light-emitting diodes (TOLEDs). It is shown that OLEDs with ITO cathodes deposited by MSTS show much lower leakage current (9.2×10−5mA∕cm2) at reverse bias of −6V as compared to that (1×10−1–10−2mA∕cm2 at −6V) of OLEDs with ITO cathodes grown by conventional dc magnetron sputtering. Based on high-resolution electron microcopy, x-ray diffraction, and scanning electron microscopy results, we describe a possible mechanism by which plasma damage-free ITO films are grown and their application for TOLEDs.

Ferroelectric-gate thin-film transistors using indium-tin-oxide channel with large charge controllability

Abstract: We have fabricated and characterized ferroelectric-gate thin-film transistors (TFTs) using indium-tin-oxide (ITO) as a channel and ferroelectric Bi4−xLaxTi3O12 (BLT) as a gate insulator. We have obtained a typical n-channel transistor property with clear current saturation in drain current and drain voltage (ID–VD) characteristics. The obtained on∕off current ratio is more than 104 and the field-effect mobility is estimated 9.1cm2∕Vs. In particular, we demonstrate a large “on”-current of 2.5 mA in ITO∕BLT structure TFT in spite of the low channel mobility. This is because the ferroelectric film can induce large charge density due to the spontaneous polarization.

Nanoscale Conjugated-Polymer Light-Emitting Diodes

Abstract: We use e-beam lithography to pattern an indium tin oxide (ITO) electrode to create arrays of conjugated-polymer LEDs, each of which has a hole-injecting contact limited to 100 nm in diameter. Using optical microscopy, we estimate that the electroluminescence from a 100 nm diameter LED comes from a region characterized by a diameter of ∼170 nm. This apparent broadening occurs due to current spreading within a PEDOT:PSS layer which was included to aid hole injection.

Properties of ITO on PET film in dependence on the coating conditions and thermal processing

Abstract: Thin films of indium tin oxide (ITO) were deposited onto plastic web (PET) by reactive DC magnetron sputtering from a ceramic target of In 2 O 3 /SnO 2 (90:10). The layer thickness and partial pressure of H 2 O were varied. After coating, the PET was heated up to 175 °C by various annealing steps. The films were then examined by XRD, SEM, UV/VIS/NIR spectroscopy, and optical light microscopy. The sheet resistivity was also measured. With a low H 2 O partial pressure of 3.2 · 10 −5 Pa, polycrystalline ITO layers were deposited. At a higher H 2 O partial pressure of 3.06 · 10 −3 Pa, the ITO layers were grown with an amorphous structure. Shrinkage of the PET substrate during the annealing process initiated severe cracking in the ITO layer. The magnitude of crack formation was found to depend on three parameters; annealing temperature, layer structure, and layer thickness. Moreover, crack formation decreased the ITO film quality by increasing the sheet resistance.

Visible electroluminescence from silicon nanocrystals embedded in amorphous silicon nitride matrix

Abstract: Visible electroluminescence from silicon nanocrystals (Si-NCs) embedded in amorphous silicon nitride (a‐SiNx) films has been observed. The Si‐NC∕a‐SiNx films were deposited by evaporating silicon from electron gun into the inductively coupled plasma of nitrogen. The density of Si-NCs in the a‐SiNx matrix was around 1012cm−2. Strong room temperature photoluminescence was observed in 2.8 and 3.0eV, different from literature values. The electroluminescence (EL) devices were fabricated with Si‐NCs∕a‐SiNx film as the active layer using the Al or Ca∕Ag cathode and the indium tin oxide anode. Through tunneling, the electrons and holes were respectively injected from the cathode and anode into Si-NCs and confined within Si-NCs for light emission by the high band gap a‐SiNx matrix. For the device with Ca∕Ag cathode, the turn-on voltage was as low as 10V and the EL efficiency was about 1.6×10−1 Cd∕A. The EL spectra consisted of two broad peaks centered around 2.5 and 2.8eV. Our results demonstrate that Si‐NCs∕a‐SiN...

The structural and optical properties of Cu2O films electrodeposited on different substrates

Abstract: Cuprous oxide films were successfully electrodeposited onto three different substrates through the reduction of copper lactate in alkaline solution at pH = 10. The substrates include indium tin oxide film coated glass, n-Si wafer with (001) orientation and Au film evaporated onto Si substrate. The substrate effects on the structural and optical properties of the electrodeposited films are investigated by in situ voltammetry, current versus time transient measurement, ex situ x-ray diffraction, scanning electron microscopy, UV–vis transmittance and reflectance and photoluminescence techniques. The results indicate that the choice of substrate can strongly affect the film morphology, structure and optical properties.

Comparison of the Electrical, Optical, and Electrochemical Properties of Diamond and Indium Tin Oxide Thin-Film Electrodes

Abstract: The electrical, optical, and electrochemical properties of an optically transparent diamond electrode are reported on and compared with those of a commonly used optically transparent electrode (OTE), indium tin oxide (ITO). The OTE was formed by coating a thin film (ca. 0.5−1 μm) of boron-doped diamond on quartz. The electrode possesses an electrical resistivity of 10-2 Ω cm, or less, and an optical transparency of ca. 55% between 300 and 900 nm. The properties were evaluated before and after 48 h exposure tests to different organic solvents (hexane, toluene, methanol, and dichloromethane) and aggressive aqueous solutions (1 M HNO3 and 1 M NaOH) and 2 h electrochemical polarizations in the same aqueous media. In contrast to ITO, the electrical and optical properties of the diamond OTE were stable during all the aqueous solution and organic solvent soak tests and during 2 h electrochemical polarizations at maximum anodic and cathodic current densities of ≥5 mA/cm2. The electrochemical properties of the dia...

Solvent effect on synthesis of indium tin oxide nano-powders by a solvothermal process

Abstract: Well-crystallized and nano-sized indium tin oxide (ITO) powders were prepared by a solvothermal process from a mixed solution consisting of indium nitrate and tin chloride. The characteristics of the solvothermally synthesized ITO powders were studied to investigate the contribution of the processing variables (solvent, working temperature, working pressure) on the physico-chemical properties. The results of this study show that the nano-sized blue ITO powders with a single phase could be directly obtained by changing the medium from water to organic solvent. Comparison of the yellow ITO powders synthesized by the coprecipitation using calcination of precipitates and blue ITO powders synthesized by the solvothermal process indicated that the solvothermal process led to an in situ reduction reaction. Solvent viscosity in the solvothermal process strongly influences both electrical and optical properties of ITO materials for transparent conducting oxides (TCOs). The size of synthesized ITO particles increased with increasing solvent viscosity due to steric hindrance. Moreover, the shape of the synthesized ITO particles became more square with increasing solvent viscosity, because the preferred orientation of ITO materials for crystallization is the fastest in the 〈1 0 0〉 direction.

Near-infrared photoconductive and photovoltaic devices using single-wall carbon nanotubes in conductive polymer films

Abstract: We have fabricated prototypical Al/single-wall carbon nanotube (SWNT)-polymer/indium tin oxide thin-film devices that exhibit promising photoconductive and photovoltaic responses in a broad spectral range, typically from 300to1600nm. This achievement was made possible by finely dispersed SWNT powders in polymer matrices such as poly-phenylene-vinylene and poly-thiophene. These devices utilize (i) the intrinsic near-infrared light harvesting properties of semiconducting SWNTs, (ii) the electronic transport properties of both semiconducting and metallic SWNTs in combination with those of the polymer matrices, and (iii) probably charge/energy transfer processes between SWNTs and the polymers. By selecting different sources of SWNTs and polymers, we have shown that the optoelectronic properties of these devices are potentially tunable. To support our investigation, several techniques including spectrally resolved photoconductivity, optical absorption, and photoluminescence spectroscopy were utilized.

Characterization of the physical and electrical properties of Indium tin oxide on polyethylene napthalate

Abstract: Indium tin oxide (ITO) thin films, on polyethylene napthalate (PEN) of both good electrical and optical properties were obtained by radio-frequency sputtering. The optoelectronic properties of the ITO films on PEN substrate were evaluated in terms of the oxygen content and the surface morphology. Rutherford backscattering spectrometry analysis was used to determine the oxygen content in the film. Hall-effect measurements were used to evaluate the dependence of electrical properties on oxygen content. The results showed that the resistivity of the ITO film increases with increasing oxygen content. For an oxygen content of 1.6×1018–2.48×1018atoms∕cm2, the resistivity varied from 0.38×10−2to1.86×10−2Ωcm. Typical resistivities were about ∼10−3Ωcm. UV-Vis spectroscopy and atomic force microscopy measurements were used to determine the optical transmittance and surface roughness of ITO films, respectively. Optical transmittances of ∼85% were obtained for the ITO thin films. Our results revealed that substrate r...

Photovoltaic structure with a conductive nanowire array electrode

Abstract: A photovoltaic (PV) structure is provided, along with a method for forming a PV structure with a conductive nanowire array electrode The method comprises: forming a bottom electrode with conductive nanowires; forming a first semiconductor layer of a first dopant type (ie, n-type) overlying the nanowires; forming a second semiconductor layer of a second dopant type, opposite of the first dopant type (ie, p-type), overlying the first semiconductor layer; and, forming a top electrode overlying the second semiconductor layer The first and second semiconductor layers can be a material such as a conductive polymer, a conjugated polymer with a fullerene derivative, and inorganic materials such as CdSe, CdS, Titania, or ZnO The conductive nanowires can be a material such as IrO2, In2O3, SnO2, or indium tin oxide (ITO)