Surface Properties Of Indium Tin Oxide Research Articles

Electrical Properties Of The OLED With Convergence Relation By Surface Treatment Methods

ITO (indium-tin-oxide) is used widely as the anode electrode in organic electroluminescence devices (OLEDs). Several studies have dealt with the effect of ITO chemical treatment but to the OLEDs performance have not been considered the effect of this treatment. We were present here results regarding these effect.We studies of the effect of surface treatments on the properties of ITO substrate. We were performed chemical treatment with RCA and Aqua regiaof the OELDs. Since we will understand the properties of OELDs, we were performed Fowler-Nordheim tunneling. The buffer layer and ITO surface treatment were performed to increase the efficiency of the OLEDs. As a result, we were obtained conform the surface properties of ITO can be significantly changed by chemical treatment. The oxygen decrease produced by chemical treatment lead to increase of oxygen vacancies. We conformed that the oxygen vacancies role on increasing carrier injection. A study on the cause of improving the performance of the device using the surface treatment and the usingthe buffer layer will be of great help in understanding the relationship between the properties of the ITO substrate and the organic electroluminescent device.

Differences in ITO Interface Characteristics Change According to the Formation of Aromatic-Ring and Aliphatic Self-Assembled Monolayers

Herein, we confirm the performance difference according to the structure of self-assembling monolayer (SAM) and investigate the characteristics of the indium tin oxide (ITO) surface when ITO substrates are deposited by (3,3,3-trifluoropropyl)trimethoxysilane (F-3SAM) and (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (F-10SAM) having different chain lengths with trifluoromethyl group as terminal functional group, as well as SAM benzoic acid (BA) and 2-naphthoic acid (NA) with benzene ring forms. Through these, it is possible to control the wetting properties, surface roughness, and work function of the ITO surface. Wetting characteristics, average roughness, and changes in work function of the ITO surface were characterized by contact angle measurement, atomic force microscopy (AFM), and UV photoelectron spectroscopy (UPS). The measured contact angles were 41.1°, 82.25°, and 118° for the bare ITO, NA, and F-10SAM, respectively, the average roughnesses of the SAM-modified surfaces were 1.377, 1.033, and 0.838 nm for the bare ITO, NA, and F-10SAM, respectively. The work function of the ITO surface modified with NA and F-10SAM increased from 0.21 and 0.36 eV to 5.01 and 5.16 eV, respectively. As a result, the surface properties of ITO were better for aliphatic SAM than for aromatic ring SAM.

Microwave exposure as a fast and cost-effective alternative of oxygen plasma treatment of indium-tin oxide electrode for application in organic solar cells

Pre-treatment methods are commonly employed to clean as well as to modify electrode surfaces. Many previous reports suggest that modifying the surface properties of indium tin oxide (ITO) by oxygen plasma treatment is a crucial step for the fabrication of high performance organic solar cells. In this work, we propose a fast and cost-effective microwave exposure step for the modification of the surface properties of ITO anode electrodes used in organic solar cells. It is demonstrated that a short microwave exposure improves the hydrophilicity and reduces the roughness of the ITO surface, as revealed by contact angle and atomic force microscopy (AFM) measurements, respectively, leading to a better quality of the PEDOT:PSS film coated on top of it. Similar results were obtained with the commonly used oxygen plasma treatment of ITO suggesting that microwave exposure is an effective process for modifying the surface properties of ITO with the benefits of low-cost, easy and fast processing. In addition, the influence of the microwave exposure of ITO anode electrode on the performance of an organic solar cell based on the poly(3-hexylthiophene):[6,6]-phenyl C70 butyric acid methyl ester (P3HT:PC70BM) blend is investigated. The 71% efficiency enhancement obtained in the microwave annealed-ITO based device as compared to the device with the as-received ITO was mainly attributed to the improvement in the short circuit current (Jsc) and decreased leakage current caused by the reduced series and the increased shunt resistances and also by the higher charge generation efficiency, and the reduced recombination losses.

Multi-Chlorine-Substituted Self-Assembled Molecules As Anode Interlayers: Tuning Surface Properties and Humidity Stability for Organic Photovoltaics.

Self-assembled small molecules (SASMs) are effective materials to improve the interfacial properties between a metal/metal oxide and the overlying organic layer. In this work, surface modification of indium tin oxide (ITO) electrode by a series of Cl-containing SASMs has been exploited to control the surface properties of ITO and device performance for organic photovoltaics. Depending on the position and degrees of chlorination for SASMs, we could precisely manipulate the work function of the ITO electrode, and chemisorption of SASMs on ITO as well. Consequently, a power conversion efficiency (PCE) of 9.1% was achieved with tetrachlorobenzoic acid (2,3,4,5-CBA) SASM by a simple solution-processed method based on PTB7-Th-PC71BM heterojunction. More intriguingly, we discover that device performance is closely associated with the humidity of ambient conditions. When the humidity increases from 35-55% to 80-95%, device performance with 2,3,4,5-CBA has negligible reduction, in contrast with other SASMs that show a sharp reduction in PCEs. The increased device performance is primarily attributed to a matched work function, stable chemisorption, and beneficial wettability with overlying active layer. These findings suggest an available approach for manufacturing inexpensive, stable, efficient, and environmentally friendly organic photovoltaics by appropriate self-assembled small molecules.

Effect of ITO surface properties on SAM modification: A review toward biosensor application

AbstractThe aim of this review is to discuss the effect of physical and chemical properties of Indium tin oxide (ITO) thin film on its self-assembled monolayer (SAM) modification, as well as device performance toward biosensor applications. The emphasis is on surface morphology studies of the thin films in order to provide connecting points between surface properties with the broader field of material science of ITO. The morphology of SAM film deposited on it directly affects by the properties of these prepared ITO film. Thus, it is a topic of interest to study the influence of physiochemical properties of this film on device fabrication and applications as biosensor platform.

Progress in Modification of Indium-Tin Oxide/Organic Interfaces for Organic Light-Emitting Diodes

The oxide/organic interfaces play crucial roles in the hole injection from the anode electrodes to the emitting organics in organic light-emitting diodes (OLEDs), and hence have strong impacts on the efficiencies and other properties of the devices. Indium-tin oxide (ITO) is currently the most popular anode material used in OLEDs due to several merits, such as good etch ability, good adherence, high transparency, low resistivity, and high work function. Interfacial engineering between the ITO electrode and the overlying organic layers is an important process to obtain the high performance of the diode devices. In this article, recent progress in modification of the ITO/organic interfaces is reviewed, as these interfaces are important to the development of the technologies aiming at improving the electroluminescence, and efficiencies as well as reducing the operation voltages of OLEDs. ITO/Organic interfacial properties can be controlled or modified by simply changing the surface properties of ITO using chemical or physical treatments, and by adding a buffer layer (e.g., metal, oxide, or organic thin films) between the ITO and hole transport or emitting organic layers. The literature data showed that the electroluminescence, efficiencies, and lifetimes of the OLEDs could be greatly increased and the operation voltage considerably decreased when the ITO/organic interfaces have been properly improved.

Investigation of surface properties of treated ITO substrates for organic light-emitting devices

In this work, a study of the surface properties of treated indium tin oxide (ITO) substrates is reported. We used three different cleaning treatments among others: washing in an ultrasonic bath of acetone and ethyl alcohol or isopropyl alcohol in room temperature as well as dipping into solution (prepared from NH4OH (25 %), H2O2 (30 %) and distilled water) at 60 °C. The relation between ITO morphology and surface properties has been studied by contact angle, and surface energy measurements as well as the surface roughness of ITO samples evaluation by atomic force microscopy (AFM). Experimental results show that the ITO surface properties are closely related to the treatment methods. The ultrasonic degreasing in acetone and ethyl alcohol yields the highest surface energy (38.5 mJ/m2), brings about the maximum reduction in contact angles and causes the smallest increasing the surface roughness of ITO substrates.

The Modification of Indium Tin Oxide with Phosphonic Acids: Mechanism of Binding, Tuning of Surface Properties, and Potential for Use in Organic Electronic Applications

Transparent metal oxides, in particular, indium tin oxide (ITO), are critical transparent contact materials for applications in next-generation organic electronics, including organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs). Understanding and controlling the surface properties of ITO allows for the molecular engineering of the ITO-organic interface, resulting in fine control of the interfacial chemistries and electronics. In particular, both surface energy matching and work function compatibility at material interfaces can result in marked improvement in OLED and OPV performance. Although there are numerous ways to change the surface properties of ITO, one of the more successful surface modifications is the use of monolayers based on organic molecules with widely variable end functional groups. Phosphonic acids (PAs) are known to bind strongly to metal oxides and form robust monolayers on many different metal oxide materials. They also demonstrate several advantages over other functionalizing moieties such as silanes or carboxylic acids. Most notably, PAs can be stored in ambient conditions without degradation, and the surface modification procedures are typically robust and easy to employ. This Account focuses on our research studying PA binding to ITO, the tunable properties of the resulting surfaces, and subsequent effects on the performance of organic electronic devices. We have used surface characterization techniques such as X-ray photoelectron spectroscopy (XPS) and infrared reflection adsorption spectroscopy (IRRAS) to determine that PAs bind to ITO in a predominantly bidentate fashion (where two of three oxygen atoms from the PA are involved in surface binding). Modification of the functional R-groups on PAs allows us to control and tune the surface energy and work function of the ITO surface. In one study using fluorinated benzyl PAs, we can keep the surface energy of ITO relatively low and constant but tune the surface work function. PA modification of ITO has resulted in materials that are more stable and more compatible with subsequently deposited organic materials, an effective work function that can be tuned by over 1 eV, and energy barriers to hole injection (OLED) or hole-harvesting (OPV) that can be well matched to the frontier orbital energies of the organic active layers, leading to better overall device properties.

Spatio-temporal detachment of single cells using microarrayed transparent electrodes

This paper describes a dynamic cell manipulation approach by which cells can be selectively detached from transparent indium tin oxide (ITO) electrodes via electrochemical desorption of a self-assembled monolayer (SAM) of alkanethiol. Changes in the surface properties of ITO following modification and electrical desorption of the SAM were characterized. By using these reactions on ITO, cells were readily attached and then detached from ITO electrodes in a very rapid manner, with greater than 90% of the cells being detached within 5 min. Furthermore, we fabricated micropatterns of ITO electrodes using photolithography. Cells on the micropatterned ITO electrodes could be detached with single-cell resolution. This approach could potentially lead to on-demand harvesting or elimination of one population from others under microscopy, for a wide range of purposes.

Luminescent and electrical performance of polymer light-emitting electrochemical cells with treated indium-tin-oxide electrodes

The surfaces of indium-tin-oxide (ITO) electrodes for polymer light-emitting electrochemical cells (LECs) were modified by O2 plasma (OP) treatment. The properties of the ITO surfaces were evaluated by chemical composition, contact angle and surface energy. The influence of surface properties of the ITO electrodes on the performance of LECs was investigated in terms of the driving voltage, turn-on voltage, injection current and luminance. When the OP treatment was employed to modify the ITO electrodes, the surface properties of ITO are optimised due to the improvement of surface stoichiometry and the enhancement of wettability. And the improved surface properties benefited from the OP treatment is observed to decay with the time after the OP treatment. In addition, the luminescent and electrical performance of the devices is found to become worse with the increasing time after the OP treatment on ITO electrodes. The results demonstrate that the device performance strongly depends on the ITO surface properties and the ITO/organic interface characteristics.

Surface modification and characterization of indium–tin oxide for organic light-emitting devices

We used various treatment methods such as ethanol treatment, sodium hydroxide solution treatment, sulfur acid treatment, and oxygen plasma treatment to modify the surface of indium–tin oxide (ITO) substrates for organic light-emitting devices (OLEDs). The surface properties of the treated ITO substrates were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), contact angle, surface energy measurements, four-point probe, X-ray Diffraction (XRD) and ultraviolet-visible spectrophotometer. The results showed that the ITO surface properties were closely related to the treatment methods, and the oxygen plasma is more efficient than other treatments as it leads to smoother surface, better surface stoichiometry, higher work function and surface energy, lower sheet resistance, and higher transmission of the ITO substrates. Moreover, small molecular organic light-emitting devices (SMOLEDs) using different treated ITO substrates as anodes were fabricated and investigated. It was found that surface treatment of ITO substrates has influence upon the injection current, the turn-on voltages of light emission, luminance, efficiency and lifetime. Oxygen plasma treatment on the ITO substrate yields the highest performance of SMOLEDs due to the improvement of interface formation and electrical contact of the ITO substrate with the small molecular material blend in the SMOLEDs.

Simultaneous Oxygen Plasma and Thermal Treatments of an ITO Surface to Improve the Electrical Characteristics of Organic Light-Emitting Diodes

The electrical characteristics of organic light emitting diodes (OLEDs) were improved by lowpower oxygen plasma processing of an indium tin oxide (ITO) surface at an elevated temperature of 500 ◦C in this work. ITO is widely used as a transparent electrode in light-emitting devices, and OLED device performance is sensitive to the surface properties of ITO. In this research, a simultaneously oxygen-plasma and thermally treated ITO surface showed better device performance than an oxygen-plasma-treated ITO surface in terms of current density, brightness, and power efficiency. OLED devices with the structure of ITO/TPD/Alq3/LiF/Al were fabricated, and the surface properties of ITO were investigated by using various characterization techniques. The work function of the modified ITO, as determined by using ultraviolet photoelectron spectroscopy (UPS), increased from 4.70 to 5.17 eV. An X-ray photoelectron spectroscopy (XPS) analysis showed an oxygen fraction change from 59.9 % to 70.1 % after the surface treatment. Based on the measurements, we conclude that hole injection is improved due to the high electronegativity of the oxygen adsorbed on the ITO surface. The XPS analysis also showed that the surface carbon composition decreased from 15.1 % to 4.67 % after the surface treatment. A reduction in carbon contamination is also attributed to the improvement in the electrical characteristics. Thus, we demonstrated that simultaneous oxygen plasma and thermal treatment is a proper way for improving the electrical characteristics of OLED devices.

Influence of electrode characteristics on the performance of organic light-emitting devices

Indium-tin oxide (ITO) substrates were treated by oxygen plasma for organic light-emitting devices (OLEDs). Using the ITO substrates aged for various times as hole-injecting electrodes, the double-layered OLEDs were fabricated by the vacuum sublimation technique, and the aging effect of treated ITO anodes on the performance of OLEDs was studied with respect to the electroluminescence efficiency, brightness and driving voltage. Experimental results reveal that the luminescent and electrical characteristics of the OLEDs are strongly dependent on the properties of the ITO anodes, and the ITO anodes aged for various times result in significant differences in device performance, which become worse with the increment of the aging time. The measurements of X-ray photoelectron spectroscopy (XPS) and surface energy show that carbon concentration increases, oxygen concentration reduces and surface energy decreases, and thereby the improved surface properties of ITO tend to decay, as the aging time increases. It indicates that the device performance of the OLEDs is closely related to the surface characteristics of the ITO anodes.

Combined AFM, XPS, and contact angle studies on treated indium–tin-oxide films for organic light-emitting devices

In the present work, surface modifications were performed on the indium–tin-oxide (ITO) substrates and the treated ITO surface properties were investigated by different characterization techniques. AFM and XPS methods were applied to measure surface roughness and chemical composition, respectively. Standard goniometry was used to determine contact angle and to calculate surface energy. Experimental results show that the ITO surface properties are subjected to the treatment methods which lead the surface to a certain degree of changes. Wettability of the modified surfaces was then monitored as a function of time elapsed after treatment and quantified. Furthermore, the polymer light-emitting electrochemical cells (LECs) with the differently treated ITO substrates as device electrodes were fabricated and characterized. We observe that the electrical and optical performances of the polymer LECs are affected by the treatment methods on the ITO surface which result in the modification of interface formation and electrical contact of the ITO substrate with the polymer blend in the polymer LECs.

High-Efficiency Blue Organic Light-Emitting Diodes Using C[sub 60] as a Surface Modifier on Indium Tin Oxide

C 60 was introduced as a modifier on indium tin oxide (ITO) and the effect of C 60 modification on light-emitting efficiency of blue organic light-emitting didoes was investigated. Device performances of C 60 modified devices were greatly dependent on ITO surface properties and C 60 thickness. Power efficiency of blue devices was improved by 80% by C 60 buffer layer on ITO because of low driving voltage and balanced electron-hole recombination.

Surface treatments of indium‐tin oxide substrates for polymer electroluminescent devices

AbstractIn this work, three different sets of processing techniques (wet, dry, and combined treatments) were utilized to modify the surfaces of indium‐tin oxide (ITO) substrates for polymer electroluminescent devices (PELDs), and the influence of surface treatments on the surface properties of ITO substrates were investigated by X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle, and four‐point probe. The surface energies of ITO substrates were also calculated from the measured contact angles. Experimental results show that the surface properties of the ITO substrates strongly depend on the surface treatments. Oxygen plasma treatment effectively improves the ITO surface properties since plasma decreases the surface roughness and sheet resistance, improves the surface stoichiometry and wetting. Furthermore, the PELDs with the differently treated ITO substrates as hole‐injecting electrodes were fabricated and characterized. We observe that the optical and electrical characteristics of devices are greatly influenced by the surface treatments on ITO substrates. Oxygen plasma treatment decreases turn‐on voltage, increases brightness and efficiency, and thereby improves the device performance of PELDs. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Oxygen plasma treatment effects of indium-tin oxide in organic light-emitting devices

The effects of oxygen plasma treatment on the surface properties of indium-tin oxide (ITO) substrates and its aging were investigated by X-ray photoelectron spectroscopy (XPS), contact angle, surface energy and polarity measurements. Experimental results demonstrate that the oxygen plasma treatment improves the stoichiometry of the surface and enhances the ITO wetting, so as to improve the surface properties of ITO substrates, due to the introduction of oxygen and the partial removal of hydrocarbon contaminants from the ITO surfaces. With the increment of aging time, however, the improved ITO surface properties are observed to tend to decay. Furthermore, the aging effect of treated ITO substrates on the performance of organic light-emitting devices (LEDs) was studied with respect to the driving voltage, brightness and efficiency. It is found that the device performance is subjected to the ITO surface properties and the ITO substrates aged for various times result in significant differences in electrical and optical characteristics which become worse as the aging time increases. The results indicate that the performance of organic LEDs is closely related to the surface properties of ITO substrates and the interface characteristics of ITO/organic layer.

Surface modification and characterization of indium–tin oxide for organic light-emitting devices

In this work, we used different treatment methods (ultrasonic degreasing, hydrochloric acid treatment, and oxygen plasma) to modify the surfaces of indium–tin oxide (ITO) substrates for organic light-emitting devices. The surface properties of treated ITO substrates were studied by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), sheet resistance, contact angle, and surface energy measurements. Experimental results show that the ITO surface properties are closely related to the treatment methods, and the oxygen plasma is more efficient than the other treatments since it brings about smoother surfaces, lower sheet resistance, higher work function, and higher surface energy and polarity of the ITO substrate. Moreover, polymer light-emitting electrochemical cells (PLECs) with differently treated ITO substrates as device electrodes were fabricated and characterized. It is found that surface treatments of ITO substrates have a certain degree of influence upon the injection current, brightness, and efficiency, but hardly upon the turn-on voltages of current injection and light emission, which are in agreement with the measured optical energy gap of the electroluminescent polymer. The oxygen plasma treatment on the ITO substrate yields the best performance of PLECs, due to the improvement of interface formation and electrical contact of the ITO substrate with the polymer blend in the PLECs.

The surface properties of treated ITO substrates effect on the performance of OLEDs

Surface modification was performed on the indium-tin-oxide (ITO) substrates for organic light-emitting diodes (OLEDs) by oxygen plasma. The effects of oxygen plasma treatment on the surface properties of ITO substrates and its aging were investigated by the measurements of the chemical composition. contact angle and surface energy. We observe that oxygen plasma treatment improves the stoichiometry of the surface and enhances ITO wetting, so as to improve the surface properties of ITO substrates. With the increment of storage time, however, the improved ITO surface properties tend to decay and the surface energy decreases. Furthermore, we studied the effect of aging variation of surface properties of treated ITO substrates on the performance of OLEDs, in terms of driving voltage, luminance, and efficiency. The device performance of the OLEDs was found to become worse with the increasing storage time after oxygen plasma on ITO substrates. The results demonstrate that the device performance of the OLEDs strongly depends on the surface properties of the ITO substrates.

Surface modifications of ITO electrodes for polymer light-emitting devices

Surface modifications were performed on the indium tin oxide (ITO) substrates for polymer light-emitting devices, using the different treatment methods including solvent cleaning, hydrochloric acid treatment and oxygen plasma. The influence of modifications on the surface properties of ITO electrodes were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle, and four-point probe. The surface energies of the ITO substrates were also calculated from the measured contact angles. Experimental results demonstrate that the surface properties of the ITO substrates strongly depend on the modification methods, and oxygen plasma more effectively improves the ITO surface properties compared with the other treatments. Furthermore, the polymer light-emitting electrochemical cells (LECs) with the differently treated ITO substrates as device electrodes were fabricated and characterized. It is observed that the surface modifications on ITO electrodes have a certain degree of influence upon the injection current, luminance and efficiency, but hardly upon the turn-on voltages of current injection and light emission which are close to the measured energy gap of electroluminescent polymer. Oxygen plasma treatment on the ITO electrode yields the better performance of the LECs, due to the improvement of interface formation and electrical contact of the ITO electrode with the polymer blend in the LECs.