Structure Of Indium Tin Oxide Research Articles

On the structure and surface chemical composition of indium–tin oxide films prepared by long-throw magnetron sputtering

Structures and surface chemical composition of indium tin oxide (ITO) thin films prepared by long-throw radio-frequency magnetron sputtering technique have been investigated. The ITO films were deposited on glass substrates using a 20 cm target-to-substrate distance in a pure argon sputtering environment. X-ray diffraction results showed that an increase in substrate temperature resulted in ITO structure evolution from amorphous to polycrystalline. Field-emission scanning electron microscopy micrographs suggested that the ITO films were free of bombardment of energetic particles since the microstructures of the films exhibited a smaller grain size and no sub-grain boundary could be observed. The surface composition of the ITO films was characterized by X-ray photoelectron spectroscopy (XPS). Oxygen atoms in both amorphous and crystalline ITO structures were observed from O 1 s XPS spectra. However, the peak of the oxygen atoms in amorphous ITO phase could only be found in samples prepared at low substrate temperatures. Its relative peak area decreased drastically when substrate temperatures were larger than 200 °C. In addition, a composition analysis from the XPS results revealed that the films deposited at low substrate temperatures contained high concentration of oxygen at the film surfaces. The oxygen-rich surfaces can be attributed to hydrolysis reactions of indium oxides, especially when large amount of the amorphous ITO were developed near the film surfaces.

Organic Solar Cells Using Nanoimprinted Transparent Metal Electrodes

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-

Opto-electronic properties of chromium doped indium–tin-oxide films deposited at room temperature

Indium–tin-oxide (ITO) doped chromium films were deposited on Corning 7059 glass prepared by radio frequency (RF) magnetron sputtering under various levels of sputtering power for the chromium target. Experimental results show that the surface roughness slightly decreases by co-sputtering Cr. The pure ITO films deposited at room temperature were amorphous-like. At 15 W of chromium target power, the structure of ITO: Cr film mainly consists of (2 2 2) crystallization plane, with minority of (2 1 1), (4 4 0), (6 6 2) crystallization planes. The carrier concentration of the ITO films increases with increasing the doping of chromium, however the mobility of the carrier decreases. When the sputtering power of the chromium target is at 7.5 W, there has a maximum carrier mobility of 27.3 cm 2 V −1 s −1, minimum carrier concentration of 2.47 × 10 20 cm −3, and lowest resistivity of 7.32 × 10 −4 Ω cm. The transmittance of all the chromium doped ITO films at the 300–800 nm wavelength region in this experiment can reach up to 70–85%. In addition, the blue shift of UV–Vis spectrum is not observed with the increase of carrier concentration.

Improved light extraction efficiency of GaN‐based light emitting diodes by using needle‐shape indium tin oxide p‐contact

AbstractThe high‐efficiency GaN‐based light emitting diodes (LEDs) with improved light extraction efficiency (LEE) using the needle‐shape indium tin oxide (ITO) p‐contact was successfully demonstrated. The needle‐shape ITO p‐contact was naturally grown by using electron‐beam evaporation method under the precisely controlled condition. The structure of ITO p‐contact varied sensitively from the planar‐shape to the needle‐shape with decreasing the deposition temperature and the partial oxygen pressure in the vacuum chamber. We fabricated the p‐side‐up GaN/sapphire LEDs with the needleshape ITO p‐contact and those with the planar‐shape ITO p‐contact using the same LED wafer (peak wavelength: 405 nm). The external quantum efficiency (EQE) of the needle‐shape ITO‐LEDs is 1.5 times larger than that of the planar‐shape ITO‐LEDs (at a forward current of 20 mA). This dramatic increase is attributed to the dramatic increasing of the LEE of the needle‐shape ITO‐LEDs. These results show that the optimizing shape of ITO p‐contact is the key technology to increase the EQE and the LEE of ITO‐LEDs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanoscale coaxial cables produced from vertically aligned carbon nanotube arrays grown via chemical vapor deposition and coated with indium tin oxide via ion assisted deposition

A highly conformal homogeneous indium tin oxide (ITO) thin film coating has been produced on vertically aligned carbon nanotube arrays by ion assisted deposition. The deposition process generates, in effect, a coaxial cable structure of ITO about a carbon nanotube. The deposited ITO films are uniformly 5 nm thick and have high crystallinity and excellent optical absorption properties, indicating they would be good candidates for use in solar cells, flexible electronics and displays. The materials are analyzed by scanning and transmission electron microscopy, X-ray diffraction, and visual light spectrometry.

Memory effect of nonvolatile bistable devices based on CdSe∕ZnS nanoparticles sandwiched between C60 layers

Current-voltage and conductance-voltage (G-V) measurements on three-layer Al∕C60∕CdSe nanoparticles∕C60∕indium tin oxide (ITO) structures fabricated by using a spin-coating method showed a nonvolatile electrical bistable behavior. Capacitance-voltage (C-V) measurements on Al∕C60∕CdSe nanoparticles∕C60∕ITO structures showed a clockwise hysteresis with a flatband voltage shift due to the existence of the CdSe nanoparticles, indicative of memory effects in the devices. Current-time measurements showed that the devices exhibited excellent memory retention ability at ambient conditions. Possible operating mechanisms for the memory effects in the Al∕C60∕CdSe nanoparticles∕C60∕ITO devices are described on the basis of the G-V and the C-V results.

Ultraviolet electroluminescence from organic light-emitting diode with cerium(III)–crown ether complex

Cerium-dicyclohexano-18-crown-6 complex, Ce-DC-18·C·6, was prepared and used to fabricate organic light-emitting diode (OLEDs) with structure of ITO (indium tin oxide)/CuPc (copper-phthalocyanine)/Ce-DC-18·C·6: CBP (4,4′-bis(9-carbazolyl)biphenyl)/Bu-PBD (2-(4-biphenylyl)-5-(4- tert-butylphenyl)-1,3,4-oxadiazole)/LiF/Al. In the device the emitter layer consists of Ce(III)-complex as a dopant and CBP as a host. Adopting this doping Ce(III)-complex film, the device exhibits ultraviolet (UV) emission at 376 nm and maximum UV radiance power 13 μW/cm 2 at 3 wt% Ce(III)-complex doped device is obtained, which has been improved by about two times in comparison with no Ce(III)-complex layer UV device. In terms of photoluminescence (PL) of Ce(III) ion and CBP film, we demonstrated that the two UV emissions should be assigned to be from electron transitions of 5d → 4f of the Ce(III) ion and of S 1 → S 0 of CBP molecule, respectively. Increasing in UV radiation at shorter UV wavelength is more valuable and interesting for solid lighting application because the shorter UV emission would much match with excitation bands of more organic or inorganic phosphors. The mechanism on the electroluminescence (EL) processes of Ce(III) ion was also discussed.

Fluorene-based copolymers for color-stable blue light-emitting diodes

A series of random conjugated copolymers (PFO-HBT) derived from 9,9-dioctylfluorene (DOF) and 2-hexylbenzotriazole (HBT) is prepared by the palladium-catalyzed Suzuki coupling reaction with the feed HBT molar ratio around 1%, 5% and 15%. By copolymerizing 2-hexylbenzotriazole into the backbone of polyfluorene, an efficient colorfast blue light-emitting polymer system is developed. The device with the structure of ITO (indium tin oxide)/PEDOT/PVK/PFO-HBT1/Ba/Al exhibits the highest external quantum efficiency 1.62% with luminance efficiency of 2.69 cd/A, power efficiency of 1.25 lm/W and the CIE coordinates of (0.15, 0.17). The EL spectra are stable at the increased current density and continuous operation without significant change of CIE.

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

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.

Dibenzothiophene/Oxide and Quinoxaline/Pyrazine Derivatives Serving as Electron‐Transport Materials

AbstractA series of 2,8‐disubstituted dibenzothiophene and 2,8‐disubstituted dibenzothiophene‐S,S‐dioxide derivatives containing quinoxaline and pyrazine moieties are synthesized via three key steps: i) palladium‐catalyzed Sonogashira coupling reaction to form dialkynes; ii) conversion of the dialkynes to diones; and iii) condensation of the diones with diamines. Single‐crystal characterization of 2,8‐di(6,7‐dimethyl‐3‐phenyl‐2‐quinoxalinyl)‐5H‐5λ6‐dibenzo[b,d]thiophene‐5,5‐dione indicates a triclinic crystal structure with space group P1 and a non‐coplanar structure. These new materials are amorphous, with glass‐transition temperatures ranging from 132 to 194 °C. The compounds (Cpd) exhibit high electron mobilities and serve as effective electron‐transport materials for organic light‐emitting devices. Double‐layer devices are fabricated with the structure indium tin oxide (ITO)/Qn/Cpd/LiF/Al, where yellow‐emitting 2,3‐bis[4‐(N‐phenyl‐9‐ethyl‐3‐carbazolylamino)phenyl]quinoxaline (Qn) serves as the emitting layer. An external quantum efficiency of 1.41 %, a power efficiency of 4.94 lm W–1, and a current efficiency of 1.62 cd A–1 are achieved at a current density of 100 mA cm–2.

Highly Efficient Electroluminescence from Green‐Light‐Emitting Electrochemical Cells Based on CuI Complexes

AbstractThe complexes [Cu(dnbp)(DPEphos)]+(X–) (dnbp and DPEphos are 2,9‐di‐n‐butyl‐1,10‐phenanthroline and bis[2‐(diphenylphosphino)phenyl]ether, respectively, and X– is BF4–, ClO4–, or PF6–) can form high‐quality films with photoluminescence quantum yields of up to 71 ± 7 %. Their electroluminescent properties are studied using the device structure indium tin oxide (ITO)/complex/metal cathode. The devices emit green light efficiently, with an emission maximum of 523 nm, and work in the mode of light‐emitting electrochemical cells. The response time of the devices greatly depends on the driving voltage, the counterions, and the thickness of the complex film. After pre‐biasing at 25 V for 40 s, the devices turn on instantly, with a turn‐on voltage of ca. 2.9 V. A current efficiency of 56 cd A–1 and an external quantum efficiency of 16 % are realized with Al as the cathode. Using a low‐work‐function metal as the cathode can significantly enhance the brightness of the device almost without affecting the turn‐on voltage and current efficiency. With a Ca cathode, a brightness of 150 cd m–2 at 6 V and 4100 cd m–2 at 25 V is demonstrated. The electroluminescent performance of these types of complexes is among the best so far for transition metal complexes with counterions.

Microstructure investigations of indium tin oxide films cosputtered with zinc oxide at room temperature

X-ray diffraction coupled with atomic force microscopy measurements were employed to investigate the cosputtered oxide films at various zinc content [Zn∕(Zn+In)at.%] atomic ratios prepared at room temperature using rf cosputtering indium tin oxide (ITO) and zinc oxide (ZnO) targets simultaneously. The crystalline structure of a pure ITO film is polycrystalline with obvious diffraction peaks of (222) and (400). As the atomic ratio reaches 26%, the cosputtered oxide film evolves from a polycrystalline ITO structure into an amorphouslike ZnkIn2Ok+3 structure. This structure also dominates the cosputtered oxide films at the atomic ratios raging from 26% to 54%. The formation of amorphouslike ZnkIn2O3+k structures is found to markedly reduce the associated film resistivity and performs a superior surface uniformity. At an atomic ratio of 60%, a diffraction peak identifies as ZnO (100) phase appears to pile on the original amorphous domain. This phase is attributed to the substitution of In3+ sites in the ITO structure unit by Zn2+ ions. The appearance of ZnO phase is responsible for the increase of film resistivity. In addition, the smooth surface roughness contributed from the amorphous structures is therefore roughened due to the appearance of the microcrystalline ZnO structures. While the atomic ratio increases to 71%, the surface roughness and resistivity are found to further increase due to the growth of ZnO (100) phase. The optical absorption edge of these cosputtered oxide films shows an apparent redshift at ultraviolet wavelengths with incremental ZnO contents incorporating into ITO films.

Surface and interface morphology observation and photovoltaic properties of C60/conducting polymer interpenetrating heterojunction devices

Optical and photovoltaic (PV) properties of PV cells with the structure indium tin oxide (ITO)/C60/conducting polymer (CP)/Au have been investigated. The C60/CP heterojunctions in the PV cells were fabricated by spin-coating an organic solution of CP onto the C60 underlying layer. Mixed organic solvents of chloroform and toluene were used to fabricate C60/CP interpenetrating interfaces. The C60/CP interfaces were controlled by adjusting the mixture ratio of chloroform to toluene. From the optical properties and SEM observation of C60/CP heterojunctions, it has been clarified that the interpenetrating interface of C60 and CP contributes to the balance of carrier generation and carrier transport, resulting in superior PV performance.

Color Tuning of a Light-Emitting Polymer: Polyfluorene-Containing Pendant Amino-Substituted Distyrylarylene Units

We have synthesized a novel polyfluorene copolymer polyfluorene-bis(4-(diphenylamino)styryl]fluorene (PF-DPAS) by orthogonally attaching an amino-substituted distyrylarylene dye bis[4-(diphenylamino)styryl]fluorene, onto the C9 position of a fluorene unit. We have investigated this polymer's thermal properties. electronic properties (viz., absorption and photoluminescence), and electrochemical behavior. Photoluminescence studies indicate that color tuning can be achieved through efficient Forster energy transfer from the higher-energy polyfluorene backbone to the lower-energy pendant DPAS units. We have fabricated light-emitting diodes with the structure indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT)/ emitting layer/1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI)/Mg:Ag. The devices, based on blends of PF-DPAS in polyfluorene-triphenylamine-oxadiazole (PF-TPA-OXD), exhibit significant improvements in device performance relative to that of the pure PF-TPA-OXD device; we attributed this improvement to both a red-shift of the electroluminescence (EL) spectra and an enhancement in quantum efficiency. At a blend ratio of 1:20, the EL spectrum is voltage-independent and stable, and exhibits the characteristic emission of a DPAS moiety: a peak at 461 nm and Commission Internationale de l'Eclairage (CIE) coordinates of (0.15, 0.18). The maximum external quantum efficiency is 2.08 % (2.87 cd A - 1 ) at a bias of 9 V (86.1 mA cm - 2 ) with a brightness of 2467 cd m - 2 ; the maximum brightness (6916 cd m - 2 ) occurred at an applied voltage of 13 V and a current density of 361 mA cm - 2 .

Enhancement of electroplex emission by using multi-layer device structure

Electroplex emission based on poly( N-vinylcarbazole) (PVK) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) has been improved dramatically by using a multi-layer device structure indium-tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): poly(styrenesulphonic acid) (PEDOT:PSS)/PVK/BCP/PVK/BCP/LiF/Al. Electroplex emission at 595 nm has been improved about 10 times under low voltage and four times under high voltage compared to the double layer device ITO/PVK/BCP/Al. The maximum brightness of the device also has been improved about eight times. Bright white emission via electroplex formation can be obtained with Commission International d’Eclairage (CIE) coordinates (0.336, 0.320) at 26 V with a brightness of 123 cd/m 2. Based on the analysis of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the materials, we suggest the enhancement is mainly ascribed to the confinement effect of the quantum-well-like multi-layer device structure. Every hole and electron has more possibilities to cross recombination at the PVK/BCP interface.

Effect of ZnO layer on characteristics of conducting polymer/C60 photovoltaic cell

Photovoltaic properties of a photovoltaic cell with structure indium–tin oxide (ITO)/ZnO/C60/poly(3-hexylthiophene) (PAT6)/Au have been investigated. The C60/PAT6 heterojunction of this cell was fabricated by spin-coating a chloroform solution of PAT6 onto the C60 thin film formed on ZnO-coated ITO. Fabricated by this method, the photovoltaic cell has demonstrated a high efficiency for solar cells based on organic polymers, i.e. a monochromic external quantum efficiency of over 70% at the peak wavelength and a power conversion efficiency of 1.0% under AM1.5 spectral illumination of 100 mW cm−2.

Effects of Crystal Structure and Particle Size on Ethanol Gas Sensing Characteristics of Nanocrystalline ITO Thick Film

Indium tin oxide (ITO) films are widely used in optical devices for their high electrical conductivity and high transparency to visible light. Some relevant papers reported ITO thin films showed favorable sensitivity to NO2 and NO gases. However, researches on gas sensing with ITO films, especially thick films, had not been actively conducted until now. The crystal structure and particle size of ITO can be controlled in nanometer accuracy by coprecipitation method. To investigate the effects of crystal structure and particle size of nano-sized ITO powder on gas sensing properties, two kinds of ITO sensors, having cubic and rhombohedral crystal structures with 15 nm particle sizes, were investigated, and three kinds of ITO sensors having 15, 30, and 70 nm particle sizes, with the rhombohedral crystal structure, were investigated. Gas sensing properties were examined in a chamber with dry air (less than 1 ppm humidity concentration) or gaseous ethanol diluted in dry air. ITO gas sensors with the finer the particle sieze have better sensitivity than of large particle size. The sensitivity of ITO thick films were evaluated by sensing of gaseous ethanol.

Effects of thermal treatment on the electrical and optical properties of silver-based indium tin oxide/metal/indium tin oxide structures

In this article, we report the results of the study of thermal treatment effects on the electrical and optical properties of silver-based indium tin oxide/metal/indium tin oxide (IMI) multilayer films. Heat treatment conditions such as temperature and gaseous atmosphere was varied to obtain better electrical and optical properties. We obtained improved electrical properties and observed considerable shift in the transmittance curves after heat treatment. Several analytical tools such as X-ray diffraction, spectroscopic ellipsometer and spectrophotometer were used to explore the causes of the changes in electrical and optical properties. The sheet resistance of the structure was severely influenced by deposition conditions of the indium tin oxide (ITO) layer at the top. Moreover, the shift of optical transmittance could be explained on the basis of the change in refractive indices of ITO layers during heat treatment. The properties of Ag-alloy-based IMI films were compared with those of pure Ag-based ones. Some defects originating from Ag layer corrosion were observed on the surface of ITO-pure Ag–ITO structures, however, their number decreased significantly in the cases of Ag-alloys containing Pd, Au and Cu, though the resistivity values of Ag-alloys were slightly higher than those of silver. Atomic force microscopy measurement results revealed that the surface of the IMI multilayer was so smooth that it meets the required qualifications as the bottom electrode of organic light emitting diodes.

Room-temperature epitaxial growth of indium tin oxide thin films on Si substrates with an epitaxial CeO 2 ultrathin buffer

Room-temperature epitaxy of indium tin oxide (ITO) thin films was achieved on Si(111) substrates with an epitaxial CeO 2 ultrathin buffer using a pulsed laser deposition technique. The epitaxial CeO 2 buffer layer was also grown at room temperature. Reflection high-energy electron diffraction and pole figure X-ray diffraction analyses confirmed the formation of a double heteroepitaxial structure of ITO(111)/CeO 2(111)/Si(111) with the epitaxial relationship of [−110] ITO//[−110] CeO2//[1–10] Si. The junction of [ITO: 100 nm thick/CeO 2: 3 nm thick/ p-Si(111)] fabricated at room temperature exhibited solar cell properties.

High-Brightness and Low-Voltage Light-Emitting Devices Based on Trischelated Ruthenium(II) and Tris(2,2‘-bipyridine)osmium(II) Emitter Layers and Low Melting Point Alloy Cathode Contacts

Solid-state light-emitting devices (LEDs) were fabricated based on an amorphous film of Ru(bpy)3(ClO4)2 (bpy = 2,2‘-bipyridine) about 100 nm thick on indium−tin oxide (ITO) with printed low melting point alloys, such as Ga:In, Ga:Sn, and Bi:In:Pb:Sn, as cathodic contacts. A device with the structure of ITO (≤10 Ω/square)/Ru(bpy)3(ClO4)2/Ga:Sn produces a bright red emission (3500 cd/m2 at 4.0 V) centered at 660 nm. This new method of making contacts significantly simplifies the fabrication of an electroluminescence cell and has potential application in the production of LEDs by inkjet or microcontact printing. LEDs based on C12−Ru(bpy)3(ClO4)2, Ru(phenanthroline)3(ClO4)2, and Os(bpy)3(PF6)2 were also studied. Low melting point alloy contacts were also used with cells based on tris(8-hydroxyquinoline)aluminum.