Showing papers on "Indium tin oxide published in 2008"

Graphene-based liquid crystal device.

Abstract: Graphene is only one atom thick, optically transparent, chemically inert, and an excellent conductor. These properties seem to make this material an excellent candidate for applications in various photonic devices that require conducting but transparent thin films. In this letter, we demonstrate liquid crystal devices with electrodes made of graphene that show excellent performance with a high contrast ratio. We also discuss the advantages of graphene compared to conventionally used metal oxides in terms of low resistivity, high transparency and chemical stability.

Organic solar cells with solution-processed graphene transparent electrodes

Abstract: We demonstrate that solution-processed graphene thin films can serve as transparent conductive anodes for organic photovoltaic cells. The graphene electrodes were deposited on quartz substrates by spin coating of an aqueous dispersion of functionalized graphene, followed by a reduction process to reduce the sheet resistance. Small molecular weight organic solar cells can be directly deposited on such graphene anodes. The short-circuit current and fill factor of these devices on graphene are lower than those of control device on indium tin oxide due to the higher sheet resistance of the graphene films. We anticipate that further optimization of the reduction conditions will improve the performance of these graphene anodes.

Air-stable inverted flexible polymer solar cells using zinc oxide nanoparticles as an electron selective layer

Abstract: The performance and stability of unencapsulated inverted bulk-heterojunction solar cells with zinc oxide (ZnO) made by different processes as the electron selective contact are compared to conventional bulk-heterojunction solar cells. The low temperature processed inverted devices using ZnO nanoparticles on indium tin oxide plastic substrates showed high power conversion efficiency of ∼3.3%. This inverted device structure possessed much better stability under ambient conditions retaining over 80% of its original conversion efficiency after 40days while the conventional one showed negligible photovoltaic activity after 4days. This is due to the improved stability at the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Ag interface.

Raman spectroscopy of graphene on different substrates and influence of defects

Abstract: We show the evolution of Raman spectra with a number of graphene layers on different substrates, $SiO_2/Si$ and conducting indium tin oxide (ITO) plate. The G mode peak position and the intensity ratio of G and 2D bands depend on the preparation of sample for the same number of graphene layers. The 2D Raman band has characteristic line shapes in single and bilayer graphene, capturing the differences in their electronic structure. The defects have a significant influence on the G band peak position for the single layer graphene: the frequency shows a blue shift up to $12 cm^{-1}$ depending on the intensity of the D Raman band, which is a marker of the defect density. Most surprisingly, Raman spectra of graphene on the conducting ITO plates show a lowering of the G mode frequency by $\sim 6cm^{-1}$ and the 2D band frequency by $\sim 20cm^{-1}$. This red-shift of the G and 2D bands is observed for the first time in single layer graphene.

Organic Solar Cells Using Nanoimprinted Transparent Metal Electrodes

Abstract: Cost effective and highly efficient renewable energy is becoming ever more important in our age of rising energy prices and global climate change. Solar energy is a nonexhaustible and green energy. Organic solar cells (OSC) have the merits of low cost and simplistic fabrication in addition to compatibility with flexible plastic substrates over large areas. They have therefore been considered a promising energy conversion platform for clean and carbon-neutral energy production. In recent years, the power conversion efficiency of OSCs based on conjugated polymers has steadily increased through improved energy harvesting, enhanced exciton separation in improved device structures, and optimization of processing parameters, e.g., solvent evaporation time, and annealing conditions. Most OSCs are built on indium tin oxide (ITO) coated substrates because ITO offers transparency in the visible range of the electromagnetic spectrum as well as good electrical conductivity. However, ITO is not the optimum electrode for solar cell applications as it has been reported that the band structure of ITO hinders efficient photocurrent generation. Moreover, the poor mechanical stability of ITO can cause device failure when an ITO-coated flexible substrate is bent. In addition, the limited supply of indium and the increasing demand from the rapidly expanding display market have increased the cost of ITO drastically, which potentially prevents the realization of low cost and large scale OSC fabrication. Therefore, there is a strong need to find alternative materials that can replace ITO as high transparency electrode. Some examples that have been investigated recently are nanotube networks, and Ag wire grids. In this communication, we report on high transparency metal wire grid electrodes for organic solar cell applications. The high transparency metal electrodes are fabricated by nanoimprint lithography (NIL), and have several advan-

Polymer Solar Cells That Use Self‐Assembled‐Monolayer‐ Modified ZnO/Metals as Cathodes

Abstract: valuesoriginatefromthelossofchargecarriersthroughleakagepathsincluding pinholes in the films and the recombination andtrapping of the carriers during their transit through the cell,leading to a decrease in device performance.Modification of electrodes has been commonly employed toimprove the contact between the active organic layer andelectrodes. At the indium tin oxide (ITO) anode side, a thinbuffer layer of a conductive polymer, poly(3,4-ethylene-dioxylene thiophene):poly(styrene sulfonic acid) (PED-OT:PSS), is often used to increase the work-function of ITOfor effective hole collection.

A Semi-transparent Plastic Solar Cell Fabricated by a Lamination Process†

Abstract: Polymer solar cells have attracted broad research interest because of their advantageous solution processing capability and formation of low-cost, flexible, and large area electronic devices. However, the efficiency of polymer solar cells is still low compared to that of inorganic solar cells. Therefore, it is a challenge to find a polymer that has all the required properties for high efficiency devices, such as strong and broad absorption, high carrier mobility, and appropriate energy levels. One possible solution to avoid the strict material requirements is to stack two or more devices with different spectral responses, which enables more efficient utilization of solar energy. Such a solution would require a semitransparent solarcell device with high efficiency in its absorption wavelength range, while high transparency would be required in the complementary wavelength range. Semitransparent solar cells are also interesting for other appealing applications, such as energy-generating color window glasses. It is desirable that such solar cell devices can be fabricated using a low-cost strategy, such as the roll-to-roll fabrication process. One critical issue in this fabrication process is how to form the active-layer/cathode mechanic and electronic contacts. The lamination process is one very promising technique to fulfill this requirement owing to its simplicity and low cost. It has been reported to produce two-layer heterojunction solar cells; however, the method is not applicable to bulk heterojunction solar cells, nor compatible with roll-to-roll fabrication process. In this Communication, an electronic glue-based lamination process combined with interface modification is presented as a one-step process for semitransparent polymer solar-cell fabrication. The finished device is metalfree, semitransparent, flexible, self-encapsulated, and highly efficient (with a maximum external quantum efficiency of 70 % and power efficiency of 3 % under AM 1.5 global 1 sun solar illumination conditions with spectral mismatch correction). This approach represents a critical step towards the ultimate goal of low-cost polymer solar cells. The device fabrication process is illustrated in Figure 1, and can be described by the following steps. In Step I, two transparent substrates coated with a transparent conductor such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), or a high conductivity polymer, etc., are selected. In Step II, one substrate is coated with a very thin buffer layer (Cs2CO3 ) to act as the low-work-function cathode, followed by coating of the active polymer layer. Step III involves the coating of conductive polymer glue to the other transparent substrate. We used modified conducting polymer poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the electronic glue, which was spin-coated to form the adhesive anode. Step IV is the lamination process: after drying both the substrates, they are laminated together by exerting force so that the two substrates are tightly glued together. During this lamination, a plastic rod with proper hardness rolls the plastic substrate to remove air bubbles. Both substrates are heated to a temperature of 105–120 °C during the lamination process, and the finished devices are then kept on the hotplate for 5–10 min for the final heat treatment. The PEDOT:PSS was purposely modified to become adhesive, so that the two separate films formed good contact at the interface, both electronically and mechanically. In this work, this adhesive and conductive PEDOT:PSS layer was obtained by doping D-sorbitol or volemitol into PEDOT:PSS, as has been successfully demonstrated in polymer light emitting diodes. However, the efficiency of such a device is too low for application. The polymer blend used in this work is regioregular poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (RRP3HT:PCBM) in 1:1 w/w ratio. The 200 nm thick polymer blend film was deposited by the slow-growth method (or solvent annealing) to enhance device efficiency. Either glass or plastic can be used as the transparent substrate. Figure 1b shows a picture of an all-plastic solar cell. The device area is ca. 40 mm. With both cathode and anode being transparent, a semitransparent polymer solar cell is formed. The transparency (T%) of the device is shown in Figure 1c, together with the solar illumination spectrum. A transparency of around 70 % was obtained in the wavelength range where polymer/PCBM has no absorption, which makes this device suitable for application in stacking devices to make full use of the solar spectrum. This device fabrication method has many advantages over the regular procedure. First of all, no thermal evaporation process is involved in the process, and each layer is coated by a low-cost and easy solution process. Second, in contrast to the reactive metal cathode in regular devices, the cathode in C O M M U N IC A IO N

Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact†

Abstract: tion (AR) coatings, [7–10] and optical resonators. [11] In many cases, however, the unavailability of materials with desired refractive indices, particularly materials with very low refractive indices, prevents the implementation of optical components with very high performance. In addition, the choice of a material with desired refractive index often forces a compromise in other materials properties such as optical transmittance and electrical conductivity that are also important for most optoelectronic applications. Here, we show that oblique-angle deposition can be used to tailor the refractive index of a thinfilm material that is chosen for its desired material properties other than refractive index. The unique ability to control the refractive index of thin film materials allows one to eliminate Fresnel reflection, one of the fundamental limitations in lightextraction efficiency of light-emitting diodes (LEDs), by fabricating coatings whose refractive index gradually decreases from the refractive index of the active semiconductor layer to the refractive index of the surrounding medium. As an example of this concept, we present a six-layer graded-refractiveindex (GRIN) AR coating made entirely of a single material, indium tin oxide (ITO), chosen for its high conductivity, high optical transmittance, and low contact resistance with GaN. Each layer has a refractive index that is individually tuned to form a stack with refractive index graded from its dense ITO value down to the value close to that of air for an optimum AR performance. It is shown that GaInN LEDs with a GRIN ITOAR contact achieve a light-extraction efficiency enhancement of 24.3 % compared to the LEDs with dense ITO coating due to a strongly reduced Fresnel reflection at the ITO– air interface. Oblique-angle deposition is a method of growing porous thin films, and hence thin films with low-refractive index (lown), enabled by surface diffusion and self-shadowing effects during the deposition process. [12–16] In oblique-angle deposition, a random growth fluctuation on the substrate produces a shadow region that the incident vapor flux cannot reach, and a non-shadow region where incident flux deposits preferentially, thereby creating an oriented rodlike structure with high porosity. Figure 1 shows the cross-sectional scanning-electron microscopy (SEM) image of low-n ITO, which is electrically conductive and optically transparent in visible wavelengths, COMMUNICATION

Reactive Sputter Deposition

Abstract: Simulation of the Sputtering Process.- Electron Emission from Surfaces Induced by Slow Ions and Atoms.- Modeling of the Magnetron Discharge.- Modelling of Reactive Sputtering Processes.- Depositing Aluminium Oxide: A Case Study of Reactive Magnetron Sputtering.- Transport of Sputtered Particles Through the Gas Phase.- Energy Deposition at the Substrate in a Magnetron Sputtering System.- Process Diagnostics.- Optical Plasma Diagnostics During Reactive Magnetron Sputtering.- Reactive Magnetron Sputtering of Indium Tin Oxide Thin Films: The Cross-Corner and Cross-Magnetron Effect.- Reactively Sputter-Deposited Solid Electrolytes and Their Applications.- Reactive SputteredWide-Bandgap p-Type Semiconducting Spinel AB2O4 and Delafossite ABO2 Thin Films for "Transparent Electronics".- Oxide-Based Electrochromic Materials and Devices Prepared by Magnetron Sputtering.- Atomic Assembly of Magnetoresistive Multilayers.

Schottky-quantum dot photovoltaics for efficient infrared power conversion

Abstract: Planar Schottky photovoltaic devices were prepared from solution-processed PbS nanocrystal quantum dot films with aluminum and indium tin oxide contacts. These devices exhibited up to 4.2% infrared power conversion efficiency, which is a threefold improvement over previous results. Solar power conversion efficiency reached 1.8%. The simple, optimized architecture allows for direct implementation in multijunction photovoltaic device configurations.

Interface modification for highly efficient organic photovoltaics

Abstract: We present highly efficient inverted polymer:fullerene bulk-heterojunction solar cells by incorporation of a nanoscale organic interfacial layer between the indium tin oxide (ITO) and the metal oxide electron-conducting layer. We demonstrate that stacking of solution-processed organic and metal oxide interfacial layers gives highly charged selective low ohmic cathodes. The incorporation of a polyoxyethylene tridecyl ether interfacial layer between ITO and solution-processed titanium oxide (TiOx) raised the power conversion efficiency of inverted organic photovoltaics to 3.6%, an improvement of around 15% in their performance over comparable devices without the organic interfacial layer.

Transparent and conductive electrodes based on unpatterned, thin metal films

Abstract: Transparent electrodes composed of ultrathin, unpatterned metal films are investigated in planar heterojunction (PHJ) and bulk heterojunction organic photovoltaic (OPV) cells. Optimal electrode composition and thickness are deduced from electrical and optical models and experiments, enabling a PHJ-OPV cell to be realized using a silver anode, achieving power conversion efficiency parity with an analogous cell that uses an indium tin oxide anode. Beneficial aspects of smooth, unpatterned metal films as transparent electrodes in OPV cells are also discussed in the text.

Controlled Growth of Two-Dimensional and One-Dimensional ZnO Nanostructures on Indium Tin Oxide Coated Glass by Direct Electrodeposition

Abstract: A simple electrochemical deposition technique is used to deposit ZnO nanostructures with diverse morphology directly on ITO-coated glass substrates at 70 °C. The concentration of the Zn(NO3)2·6H2O electrolyte is important to controlling the dimensionality of the nanostructures, with formation of one-dimensional (1D) nanospikes and nanopillars (with 50−500 nm diameter) below 0.01 M and of two-dimensional (2D) nanowalls and nanodisks (with 50−100 nm wall/disk thickness) above 0.05 M. Glancing-incidence X-ray diffraction study shows their wurtzite structure and confirms the change in the preferred crystal plane orientation with the dimensionality of ZnO nanostructures. UV−vis spectroscopy reveals a higher transmittance from 2D nanostructures than from 1D nanostructures and their optical direct band gaps estimated to be 3.12−3.27 eV. Depth-profiling X-ray photoemission studies show the presence of Zn(OH)2 outer layers on the ZnO nanostructures, with a higher Zn(OH)2 moiety for 2D nanostructures relative to 1D...

Organic photovoltaic cells based on an acceptor of soluble graphene

Abstract: In this paper, an organic photovoltaic device based on an acceptor of solution-processable functionalized graphene was designed. A short circuit current density (Jsc) of 4.0mAcm−2, open circuit voltage (Voc) of 0.72V, and a solar power conversion efficiency of 1.1% were obtained for the device of indium tin oxide/poly(ethylene dioxythiophene) doped with polystyrene sulfonic acid (40nm)/poly(3-hexylthiophene-1, 3-diyl):graphene (graphene 10wt%, 100nm)/LiF (1nm)/Al (70nm) after an annealing treatment under simulated AM1.5G 100mW illumination in air. Because of the low price, ease of preparation, and inertness against ambient conditions, soluble graphene will be a promising candidate used for acceptor materials in the photovoltaic applications.

Surface Plasmon Polaritons and Screened Plasma Absorption in Indium Tin Oxide Compared to Silver and Gold

Abstract: This study addresses the ability of a conducting metal oxide to act as a material capable of supporting surface plasmon polaritons (SPPs). By use of a two-phase Fresnel model that provides insight into the difference between polariton-induced and absorptive decreases in reflectivity, indium tin oxide (ITO) is compared to the noble metals gold and silver, which are widely used as materials for surface plasmon resonance (SPR) detection of analytes. The study builds on application of the Drude free electron model that provides an explanation for the observed optical extinctions as a function of ITO film thickness, including the dependence of wavenumber on angle, by use of only two adjustable parameters, the plasma frequency ωp and the damping Γ. Herein, models of the dispersion and absorption include both the real and imaginary parts of the dielectric function to obtain the plasma absorption spectra and dispersion curves for ITO, Ag, and Au. ITO is found to have surface plasmon dispersion curves and plasma a...

Room-Temperature CW Lasing of a GaN-Based Vertical-Cavity Surface-Emitting Laser by Current Injection

Abstract: We report the demonstration of CW lasing at room temperature in a GaN-based vertical-cavity surface-emitting laser (VCSEL) by current injection. The active region of the VCSEL consisted of a two-pair InGaN/GaN quantum well active layer. The optical cavity consisted of a 7-λ-thick GaN semiconductor layer and an indium tin oxide layer for p-contact embedded between two SiO2/Nb2O5 dielectric distributed Bragg reflectors. The VCSEL was mounted on a Si substrate by wafer bonding and the sapphire substrate was removed by laser lift-off. Under CW operation for an 8-µm aperture device, the threshold current was 7.0 mA and the emission wavelength was approximately 414 nm.

Gallium–Indium–Zinc-Oxide-Based Thin-Film Transistors: Influence of the Source/Drain Material

Abstract: During the last years, oxide semiconductors have shown that they will have a key role in the future of electronics. In fact, several research groups have already presented working devices with remarkable electrical and optical properties based on these materials, mainly thin-film transistors (TFTs). Most of these TFTs use indium-tin oxide (ITO) as the material for source/drain electrodes. This paper focuses on the investigation of different materials to replace ITO in inverted-staggered TFTs based on gallium-indium-zinc oxide (GIZO) semiconductor. The analyzed electrode materials were indium-zinc oxide, Ti, Al, Mo, and Ti/Au, with each of these materials used in two different kinds of devices: one was annealed after GIZO channel deposition but prior to source/drain deposition, and the other was annealed at the end of device production. The results show an improvement on the electrical properties when the annealing is performed at the end (for instance, with Ti/Au electrodes, mobility rises from 19 to 25 cm2/V ldr s, and turn-on voltage drops from 4 to 2 V). Using time-of-flight secondary ion mass spectrometry (TOF-SIMS), we could confirm that some diffusion exists in the source/drain electrodes/semiconductor interface, which is in close agreement with the obtained electrical properties. In addition to TOF-SIMS results for relevant elements, electrical characterization is presented for each kind of device, including the extraction of source/drain series resistances and TFT intrinsic parameters, such as (intrinsic mobility) and VTi (intrinsic threshold voltage).

Transparent resistive random access memory and its characteristics for nonvolatile resistive switching

Abstract: This report covers the fabrication of a fully transparent resistive random access memory (TRRAM) device based on an ITO (indium tin oxide)/ZnO/ITO capacitor structure and its resistive switching characteristics. The fabricated TRRAM has a transmittance of 81% (including the substrate) in the visible region and an excellent switching behavior under 3V. The retention measurement suggests that the memory property of the TRRAM device could be maintained for more than 10years. We believe that the TRRAM device presented in this work could be a milestone of future see-through electronic devices.

Sensors for 5-hydroxytryptamine and 5-hydroxyindole acetic acid based on nanomaterial modified electrodes

Abstract: Simultaneous voltammetric determination of serotonin and 5-hydroxyindole acetic acid has been described at single walled carbon nanotube modified glassy carbon electrode and gold nanoparticles modified indium tin oxide electrode. The method described is fast, simple, accurate with detection limits as low as 32 nM for 5-hydroxytryptamine (5-HT) at single-walled carbon nanotube modified glassy carbon electrode and 27 nM for 5-hydroxyindole acetic acid (5-HIAA) at gold nanoparticles modified indium tin oxide electrode. Linear variation of peak current with change in concentration was observed in the concentration range 0.1–100 μM for 5-HT and 5-HIAA. Application of the method for non-invasive determination of the compounds in urine samples has also been described. The inter- and intra-day stability of the electrodes were also determined and electrodes were found to be sufficiently stable for 1 week.

InP nanowire/polymer hybrid photodiode.

Abstract: A novel design is presented for a nanowire/polymer hybrid photodiode. n-InP nanowires are grown directly onto an indium tin oxide (ITO) electrode to increase carrier collection efficiency and to eliminate the need for an expensive substrate. Experiments show that an ohmic contact is achieved between the nanowires and the ITO electrode. The nanowires are then enveloped by a high hole mobility conjugated polymer, poly(3-hexylthiophene). Compared to the control polymer-only device, the inclusion of InP nanowires increases the forward bias current conduction by 6-7 orders of magnitude. A high rectification ratio of 155 is achieved in these photodiodes along with a low ideality factor of 1.31. The hybrid device produces a photoresponse with a fill factor of 0.44, thus showing promise as an alternative to current polymer solar cell designs.

The origin of the hole injection improvements at indium tin oxide/ molybdenum trioxide/N,N' -bis(1-naphthyl)-N,N' -diphenyl-1,1' '-biphenyl-4,4'-diamine interfaces

Abstract: We investigated the interfacial electronic structures of indium tin oxide (ITO)/molybdenum trioxide (MoO3)/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) using in situ ultraviolet and x-ray photoemission spectroscopy to understand the origin of hole injection improvements in organic light-emitting devices (OLEDs). Inserting a MoO3 layer between ITO and NPB, the hole injection barrier was remarkably reduced. Moreover, a gap state in the band gap of NPB was found which assisted the Ohmic hole injection at the interface. The hole injection barrier lowering and Ohmic injection explain why the OLED in combination with MoO3 showed improved performance.

High-bendability flexible dye-sensitized solar cell with a nanoparticle-modified ZnO-nanowire electrode

Abstract: We report a high-bendability flexible dye-sensitized solar cell (DSSC) based on a ZnO-nanowire photoelectrode, which was fabricated on polyethylene terephtalate/indium tin oxide substrate by low-temperature hydrothermal growth. Nanowire morphology shows preferable in crack resistance due to its efficient release of bending stress. The ZnO-nanowire film can be bended to an extreme radius of 2mm with no crack observed. Flexible DSSCs based on this kind of ZnO-nanowire photoelectrodes showed good bending stability. With a ZnO-nanoparticle modification on the nanowires, the flexible DSSC fabricated showed a much improved power conversion efficiency. Meanwhile, the good bendablility of this nanoparticle-modified nanowire electrode is maintained. The results demonstrate that high quality ZnO nanowires fabricated by the low-temperature method is promising for efficient and flexible plastic solar cells.

Inverted Solution Processable OLEDs Using a Metal Oxide as an Electron Injection Contact.

Abstract: A new type of bottom-emission electroluminescent device is described in which a metal oxide is used as the electron-injecting contact. The preparation of such a device is simple. It consists of the deposition of a thin layer of a metal oxide on top of an indium tin oxide covered glass substrate, followed by the solution processing of the light-emitting layer and subsequently the deposition of a high-workfunction (air-stable) metal anode. This architecture allows for a low-cost electroluminescent device because no rigorous encapsulation is required. Electroluminescence with a high brightness reaching 5700 cd m–2 is observed at voltages as low as 8 V, demonstrating the potential of this new approach to organic light-emitting diode (OLED) devices. Unfortunately the device efficiency is rather low because of the high current density flowing through the device. We show that the device only operates after the insertion of an additional hole-injection layer in between the light-emitting polymer (LEP) and the metal anode. A simple model that explains the experimental results and provides avenues for further optimization of these devices is described. It is based on the idea that the barrier for electron injection is lowered by the formation of a space–charge field over the metal-oxide–LEP interface due to the build up of holes in the LEP layer close to this interface.