Surface Modification Of Indium Tin Oxide Research Articles

Optimizing luminous efficiency in polymer light-emitting diodes through anode oxygen-plasma treatment under diverse pressure conditions

This study investigates the impact of oxygen-plasma (O2-plasma) treatment on the microscale electrical properties of indium tin oxide (ITO) surfaces for enhancement of the luminous efficiency of polymer light-emitting diodes (PLEDs). Significant effects on conductivity distribution were observed when treatment was performed at pressures exceeding 0.4 Torr. ITO-6, the ITO treated with O2-plasma at 0.6 Torr, emerged as the preferred anode substrate for PLEDs, displaying a 72.5 % coverage of stable-conductive regions. When utilized as the anode in PLED, it exhibited a remarkable 209 % increase in average current efficiency and a 184 % enhancement in electroluminescent intensity compared to the reference PLED. These findings provide valuable insights for optimizing PLEDs through surface modification of ITO.

Surface Modification of ITO with N-Heterocyclic Carbene Precursors Results in Electron Selective Contacts in Organic Photovoltaic Devices.

Surface modification of indium tin oxide (ITO) electrodes with organic molecules is known to tune their work function which results in higher charge carrier selectivity in corresponding organic electronic devices and hence influences the performance of organic solar cells. In recent years, N-heterocyclic carbenes (NHCs) have also been proven to be capable to modify the work function of metals and semimetals compared to the unfunctionalized surface via the formation of strong covalent bonds. In this report, we have designed and performed the modification of the ITO surface with NHC by using the zwitterionic bench stable IPr-CO2 as the NHC precursor, applied via spin coating. Upon modification, the work function of ITO electrodes was reduced significantly which resulted in electron selective contacts in corresponding organic photovoltaic devices. In addition, various characterization techniques and analytical methods are used to elucidate the nature of the bound species and the corresponding binding mechanism of the material to the ITO surface.

Optoelectronic performance of indium tin oxide thin films structured by sub-picosecond direct laser interference patterning

A route to increase the efficiency of thin film solar cells is improving the light-trapping capacity by texturing the top Transparent Conductive Oxide (TCO) so that the sunlight reaching the solar absorber scatters into multiple directions. In this study, Indium Tin Oxide (ITO) thin films are treated by infrared sub-picosecond Direct Laser Interference Patterning (DLIP) to modify the surface topography. Surface analysis by scanning electron microscopy and confocal microscopy reveals the presence of periodic microchannels with a spatial period of 5 µm and an average height between 15 and 450 nm decorated with Laser-Induced Periodic Surface Structures (LIPSS) in the direction parallel to the microchannels. A relative increase in the average total and diffuse optical transmittances up to 10.7% and 1900%, respectively, was obtained in the 400–1000 nm spectral range as an outcome of the interaction of white light with the generated micro- and nanostructures. The estimation of Haacke’s figure of merit suggests that the surface modification of ITO with fluence levels near the ablation threshold might enhance the performance of solar cells that employ ITO as a front electrode.

Surface-modified ultra-thin indium tin oxide electrodes for efficient perovskite light-emitting diodes

Perovskite light-emitting diodes (PeLEDs) are promising lighting sources owing to their unique optical and electrical properties, such as high color purity and charge carrier mobility. Various material strategies have been reported to increase the radiative recombination rate and alleviate the non-radiative recombination rate of PeLEDs. However, PeLEDs are prone to low device efficiencies owing to the metal-induced exciton quenching caused by the diffusion of metal species from the indium tin oxide (ITO) electrodes into the emissive layer. Herein, we demonstrate that surface modification of ITO by means of electric-field-induced Ni doping treatment prevents the diffusion of metal species and helps tune the work function. The effects of Ni doping on ITO (Ni-ITO) are clarified by conducting X-ray photoelectron spectroscopy, time of flight-secondary ion mass spectrometry, and energy level investigations. A PeLED fabricated using Ni-ITO as the anode exhibited a maximum current efficiency of 91.11 cdA-1 and external quantum efficiency of 20.48%, which are 13.5% and 13.9% higher than those of the PeLED fabricated using a commercially available ITO film (with a thickness of 180 nm), respectively. The results of this study can be used as guidelines to increase the quantum efficiencies of ITO-based organic/inorganic emitter devices and PeLEDs.

DNA biosensor based on surface modification of ITO by physical vapor deposition of gold and carbon quantum dots modified with neutral red as an electrochemical redox probe

Here, we report on an effective modified DNA biosensor. First, the surface of an indium tin oxide (ITO) is modified with gold via physical vapor deposition technique. Second, we also report on the synthesis of carbon dots, which are modified with neutral red as an electrochemical redox probe. The different steps of modifications are monitored with atomic force microscope, UV–Vis spectroscopy, fluorescence spectroscopy FT-IR spectroscopy, dynamic light scattering and as well as different electrochemical techniques. The biosensor is applied for determination of salmonella DNA sequence at ultra-low concentrations with linear range of 20–240 fM and 10 fM limit of detection. The ability of detection of the target of biosensor is evaluated in spiked samples.

Glucose sensing performance of CuO nanoparticles and indium tin oxide surface modification on potassium-doped ZnO nanorods

Heterojunction with potassium-doped zinc oxide (ZnO) nanorods and copper oxide (CuO) nanoparticles with indium tin oxide (ITO) modification for glucose detecting applications were studied in detail. Energy band structure of p-p heterojunction enhances the current during the adsorption of glucose. CuO nanoparticles with better catalytic activity and ITO nanoparticles with high electrical conductivity improve the sensing current to a higher value. The ITO/CuO nanoparticles/ZnO:K nanorods working electrode has high sensitivity of 277.3 μAmM−1 cm−2 and superior anti-interference ability towards detection of glucose. Synthesis process is simple, inexpensive, and with no enzyme.

Solvent-resistant ITO work function tuning by an acridine derivative enables high performance inverted polymer solar cells

In order to avoid an interpenetration of the buffer and the photoactive layers during preparation of polymer solar cells (PSCs), solvent-resistant buffer films were chemically modified on indium tin oxide (ITO) surface. The conjugated aromatics acridine orange base (AOB) was introduced into the films using 3-bromopropyltrimethoxysilane (BrTMS) as coupling agent. Upon ITO surface modification, the respective work functions show a significant decrease. The modified ITO substrates were implemented in inverted PSCs based on PBDTTT-C-T:PC71BM. With the modification, the power conversion efficiency (PCE) was improved significantly from 4.10% (for the inverted PSC without this buffer layer) to 7.56%. The PCE enhancement is mainly caused by the increase of the open-circuit voltage (43%). These results indicate that the solvent-resistant film is able to facilitate electron collection and transportation, thus providing a novel route to high efficient PSCs by surface engineering.

ITO surface modification for inverted organic photovoltaics

The work function (WF) of indium-tin-oxide (ITO) substrates plays an important role on the inverted organic photovoltaic device performance. And electrode engineering has been a useful method to facilitate carrier extraction or charge collection to enhance organic photovoltaic (OPV) performance. By using self-assembly technique, we have deposited poly(dimethyl diallylammonium chloride) (PDDA) layers onto ITO coated glass substrates. The results indicate that the surface WF of ITO is reduced by about 0.3 eV after PDDA modification, which is attributed to the modulation in electron affinity. In addition, the surface roughness of ITO substrate became smaller after PDDA modification. These modified ITO substrates can be applied to fabricate inverted OPVs, in which ITO works as the cathode to collect electrons. As a result, the photovoltaic performance of inverted OPV is substantially improved, mainly reflecting on the increase of short circuit current density.

Transparent electrodes for organic optoelectronic devices: a review

Transparent conductive electrodes are one of the essential components for organic optoelectronic devices, including photovoltaic cells and light-emitting diodes. Indium-tin oxide (ITO) is the most common transparent electrode in these devices due to its excellent optical and electrical properties. However, the manufacturing of ITO film requires precious raw materials and expensive processes, which limits their compatibility with mass production of large-area, low-cost devices. The optical/electrical properties of ITO are strongly dependent on the deposition processes and treatment conditions, whereas its brittleness and the potential damage to underlying films during deposition also present challenges for its use in flexible devices. Recently, several other transparent conductive materials, which have various degrees of success relative to commercial applications have been developed to address these issues. Starting from the basic properties of ITO and the effect of various ITO surface modification methods, here we review four different groups of materials, doped metal oxides, thin metals, conducting polymers, and nanomaterials (including carbon nanotubes, graphene, and metal nanowires), that have been reported as transparent electrodes in organic optoelectronic materials. Particular emphasis is given to their optical/electrical and other material properties, deposition techniques, and applications in organic optoelectronic devices.

Effect of ITO surface modification on the OLED device lifetime.

Pretreatment of the indium tin oxide (ITO) surface is generally adopted to improve the charge injection and device performance in the fabrication of organic light-emitting diodes (OLEDs). For the common approaches of surface treatment, such as oxygen plasma treatment, self-assembled monolayer (SAM) adsorption, and the PEDOT:PSS coating, different effects on the device lifetime were observed. A distinctly different driving voltage change with device operation time was obtained and was correlated with the device lifetime. The fast increase in driving voltage for devices based on oxygen-plasma-treated ITO is attributed to the work function change as a result of the change in the composition of the interface with device operation, whereas a rather stable work function for SAM-modified ITO is suggested due to the permanent dipoles associated with the monolayer and the protecting effect of the covalently bound monolayer on the surface composition.

Systematic Investigation of Surface Modification by Organosiloxane Self-Assembled on Indium–Tin Oxide for Improved Hole Injection in Organic Light-Emitting Diodes

Various works on modification of the indium-tin oxide (ITO) substrate have been carried out so as to enhance hole injection in organic light-emitting devices. Herein, a simple and efficient approach to tuning the work function of the ITO substrate is described by surface modification of ITO with an organosiloxane self-assembled monolayer. The influences of the electronegativity on modification of the ITO substrate are systematically investigated by attaching electron-withdrawing groups (Cl, Br, and I) and an electron-donating group (NH2) to the organosiloxane materials. The preparation and modification of the ITO substrate has been studied using primarily atomic force microscopy and X-ray photoelectron spectroscopy and vacuum-ultraviolet spectroscopy, and remarkable changes have been observed after modification. The device based on a 3Cl-Si-ITO-modified anode exhibits the best efficiency among the devices, better than the control devices based on bare ITO, UV-treated ITO, and even Cl-ITO.

Performance enhancement of organic light-emitting diodes by chlorine plasma treatment of indium tin oxide

The characteristics of green phosphorescent organic light-emitting diodes (OLEDs) fabricated on ITO/glass substrates pretreated with low-energy O2 and Cl2 plasma were compared. At 20 mA/cm2, the OLEDs with O2 and Cl2 plasma-treated indium tin oxide (ITO) had voltages of 9.6 and 7.6 eV, and brightness of 9580 and 12380 cd/m2, respectively. At ∼104 cd/m2, the latter had a 30% higher external quantum efficiency and a 74% higher power efficiency. Photoelectron spectroscopies revealed that Cl2 plasma treatment created stable In-Cl bonds and raised the work function of ITO by up to 0.9 eV. These results suggest that the better energy level alignment at the chlorinated ITO/organic interface enhances hole injection, leading to more efficient and more reliable operation of the OLEDs. The developed plasma chlorination process is very effective for surface modification of ITO and compatible with the fabrication of various organic electronics.

Modification of ITO surface using aromatic small molecules with carboxylic acid groups for OLED applications

4-[(3-Methylphenyl)(phenyl)amino]benzoic acid (MPPBA) was synthesized in order to facilitate the hole-injection in Organic Light Emitting Diodes (OLED). MPPBA was applied to form self-assembled monolayer (SAM) on indium tin oxide (ITO) anode to align energy-level at the interface between organic semiconductor material (TPD) and inorganic anode (ITO) in OLED devices. The modified surface was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). KPFM was used to measure the surface potential and work function between the tip and the ITO surface modified by SAM technique using MPPBA. The OLED devices (ITO/MPPBA/TPD/Alq 3/Al) fabricated with SAM-modified ITO substrates showed lower turn-on voltages and enhanced diode current compare to the OLED devices fabricated with bare ITO substrates.

Effect of surface roughness and surface modification of indium tin oxide electrode on its potential response to tryptophan

The effect of surface modification of indium tin oxide (ITO) electrode on its potential response to tryptophan was investigated for ITO substrates with different surface roughness. It was found that a small difference in surface roughness, between ∼1 and ∼2 nm of R a evaluated by atomic force microscopy, affects the rest potential of ITO electrode in the electrolyte. A slight difference in In:Sn ratio at the near surface of the ITO substrates, measured by angle-resolved X-ray photoelectron spectrometry and Auger electron spectroscopy is remarkable, and considered to relate with surface roughness. Interestingly, successive modification of the ITO surface with aminopropylsilane and disuccinimidyl suberate, of which essentiality to the potential response to indole compounds we previously reported, improved the stability of the rest potential and enabled the electrodes to respond to tryptophan in case of specimens with R a values ranging between ∼2 and ∼3 nm but not for those with R a of ∼1 nm. It was suggested that there are optimum values of effective work function of ITO for specific potential response to tryptophan, which can be obtained by the successive modification of ITO surface.

Oxide Contacts in Organic Photovoltaics: Characterization and Control of Near-Surface Composition in Indium−Tin Oxide (ITO) Electrodes

The recent improvements in the power conversion efficiencies of organic photovoltaic devices (OPVs) promise to make these technologies increasingly attractive alternatives to more established photovoltaic technologies. OPVs typically consist of photoactive layers 20-100 nm thick sandwiched between both transparent oxide and metallic electrical contacts. Ideal OPVs rely on ohmic top and bottom contacts to harvest photogenerated charges without compromising the power conversion efficiency of the OPV. Unfortunately, the electrical contact materials (metals and metal oxides) and the active organic layers in OPVs are often incompatible and may be poorly optimized for harvesting photogenerated charges. Therefore, further optimization of the chemical and physical stabilities of these metal oxide materials with organic materials will be an essential component of the development of OPV technologies. The energetic and kinetic barriers to charge injection/collection must be minimized to maximize OPV power conversion efficiencies. In this Account, we review recent studies of one of the most common transparent conducting oxides (TCOs), indium-tin oxide (ITO), which is the transparent bottom contact in many OPV technologies. These studies of the surface chemistry and surface modification of ITO are also applicable to other TCO materials. Clean, freshly deposited ITO is intrinsically reactive toward H(2)O, CO, CO(2), etc. and is often chemically and electrically heterogeneous in the near-surface region. Conductive-tip atomic force microscopy (C-AFM) studies reveal significant spatial variability in electrical properties. We describe the use of acid activation, small-molecule chemisorption, and electrodeposition of conducting polymer films to tune the surface free energy, the effective work function, and electrochemical reactivity of ITO surfaces. Certain electrodeposited poly(thiophenes) show their own photovoltaic activity or can be used as electronically tunable substrates for other photoactive layers. For certain photoactive donor layers (phthalocyanines), we have used the polarity of the oxide surface to accelerate dewetting and "nanotexturing" of the donor layer to enhance OPV performance. These complex surface chemistries will make oxide/organic interfaces one of the key focal points for research in new OPV technologies.

Fabrication of titanium oxide/phthalocyanine hybrid multilayers and their application to interface control for an organic diode

Hybrid multilayers of phthalocyanines (Pc) and titanium oxide (TiOx) have been effectively fabricated on the surfaces of quartz and indium-tin-oxide (ITO) according to the following layer-by-layer sequence; (i) the formation of a titanium butoxide layer (Ti(OBu)m) grafted onto the substrate surface by immersion of a substrate into a solution of Ti(OBu)4, (ii) hydrolysis of Ti(OBu)m to a TiOx layer with a Ti–OH surface, (iii) dipping of the treated substrate into a solution of Pc1–Pc3 bearing four or eight (triethoxysilyl)alkoxy substituents to form a Pc layer on the TiOx surface, presumably through Ti–O–Si bonding, (iv) hydrolysis of excess Si(OEt)3 groups in the Pc layer to form a silanol surface and (v) cyclic repetition of steps (i)–(iv). Atomic force microscopy (AFM) has shown that the multilayer surfaces are smooth, with surface roughnesses similar to that of a pristine substrate. The ratios of Ti atoms/Pc molecule for three different multilayers determined by X-ray photoelectron spectroscopy (XPS) were found to be roughly constant (3.8–4.3). For hole-only diodes of ITO/N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine/Au, it has been found that the surface modification of ITO with the hybrid multilayers of Pc1 causes remarkable current enhancements at low applied biases depending on the cycle number of the layer-by-layer deposition.

Effects of ITO surface modification using self-assembly molecules on the characteristics of OLEDs

Indium tin oxide (ITO) has been commonly used as an anode of organic light emitting diode (OLED), because of relatively high work function, high transmittance, and low resistance. However, interface property between ITO and adjacent organic layer limits hole injection from the anode electrode. We have synthesized 4′-nitrobiphenyl-4-carboxylic acid (NBCA) and fabricated the hole-only device consisting of ITO/NBCA self-assembled monolayer (SAM)/TPD (1500 Å)/Al (500 Å) and the organic light emitting diode (OLED) consisting of ITO/NBCA SAM/TPD (600 Å)/Alq 3 (600 Å)/Al (600 Å). The prepared hole-only device with NBCA exhibited lower driving voltage than the device using 4-nitrobenzoic acid (NBA). OLED using NBCA also showed high external quantum efficiency.

Surface modified high rectification organic diode based on sulfonated poly(aniline)

In this paper, we present a new method that combines surface modification of indium-tin oxide (ITO) and electropolymerization to prepare thin, sulfonated poly(aniline) (SPAN) films with good surface coverage. The surface modification enhances the growth of the SPAN film resulting in a better rectification signal than for SPAN films polymerized on unmodified ITO substrates. The films were characterized by FTIR, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The sulfonation degree of SPAN was determined to 29% by X-ray photoelectron spectroscopy (XPS). UV-VIS spectroscopy shows that the pH sensitivity of SPAN is suppressed due to sulfonation of the polymer backbone. It is also shown that conversion of the SPAN film to the emeraldine salt (ES) form after polymerization is crucial for obtaining a high rectification signal. This is an important practical aspect in the preparation procedure of organic electronic devices.

Indium-tin oxide anodes modified by self-assembly for light-emitting diodes based on blue-emitting polyfluorenes

We present the electro-optical properties of light-emitting diodes (LEDs) based on two blue-emitting polyfluorenes, with aluminum cathodes and having indium-tin oxide (ITO) anodes modified by self-assembled monolayers (SAM) of benzenesulphenyl chloride derivatives. The modification of ITO surface was confirmed by contact angle measurements. Electroabsorption measurements were used to assess the modification of ITO work function upon SAM formation. We find that the use of a benzenesulphenyl chloride derivative containing a nitro group is as effective at improving LEDs characteristics as the use of a hole-injection layer of well known PEDOT:PSS.

Advanced Surface Modification of Indium Tin Oxide for Improved Charge Injection in Organic Devices

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 pi-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.