Indium Tin Oxide Anode Research Articles

Investigation of the Field Emission Stability of Sphere-Like Diamond Microcrystalline-Aggregates Films

The sphere-like diamond microcrystalline-aggregates were fabricated by microwave plasma chemical vapor deposition (MPCVD) method. The ceramic with a Ti metal layer was used as substrates. The fabricated diamond microcrystalline aggregates were evaluated by Raman scattering spectroscopy, x-ray diffraction spectrum (XRD), scanning electron microscopy (SEM). The field emission properties were tested by using a diode structure in a vacuum. A phosphor-coated indium tin oxide (ITO) anode was used for observing and characterizing the field emission. It was found that the sphere-like diamond microcrystalline-aggregates films exhibited good electron emission properties. The turn-on field was only 0.55V/μm, and emission current density as high as 11mA/cm2 was obtained under an applied field of 2.18V/μm for the first operation. After several cycling operations, the field emission tended to stable characteristics of current versus voltage. The stability evolvement and mechanism are investigated relating to microstructure of the sphere-like diamond microcrystalline-aggregates films.

Flexible Organic Light-Emitting Diodes with Amorphous ITO Anodes on Transparent Cellulose Substrates

We describe flexible organic light-emitting diodes (OLEDs) with indium tin oxide (ITO) anodes fabricated at low substrate temperatures using facing target sputter (FTS) on a transparent-cellulose substrates. The device structure was cellulose paper substrate/SiO2/ITO/NPB/Alq3:C545T/BCP/LiF/Al. The ITO thin films were deposited at substrate temperatures below 70°C. X-ray diffraction analysis revealed that the ITO thin films were amorphous. As the substrate temperature during deposition increased from 27 to 70°C, the sheet resistivity decreased from 1,400 to 120 Ω/□. The OLEDs with ITO thin film anode with sheet resistivity of 120 Ω/□ exhibited a maximum luminance of 14,543 cd/m2 at a driving voltage of 14.75 V.

Improved device reliability in organic light emitting devices by controlling the etching of indium zinc oxide anode

A controllable etching process for indium zinc oxide (IZO) films was developed by using a weak etchant of oxalic acid with a slow etching ratio. With controllable etching time and temperature, a patterned IZO electrode with smoothed surface morphology and slope edge was achieved. For the practical application in organic light emitting devices (OLEDs), a suppression of the leak current in the current—voltage characteristics of OLEDs was observed. It resulted in a 1.6 times longer half lifetime in the IZO-based OLEDs compared to that using an indium tin oxide (ITO) anode etched by a conventional strong etchant of aqua regia.

Efficiency enhancement of organic light-emitting devices by using honeycomb metallic electrodes and two-dimensional photonic crystal arrays

In this paper, a facile fabrication technique called nanosphere lithography combining with two-step reactive ion etching method for patterning honeycomb metallic electrode with high transparency and excellent uniformity is demonstrated. The patterning silver electrode with 15-nm film thickness and 68.6% fill-factor was used as the organic light-emitting diode (OLED) anode, which showed an average transmittance of 77.4% and sheet resistance of 30.7Ω/□. The current efficiency is 8.35cd/A for the OLED with patterned silver anode under 100cd/m2 operation brightness, which was 47% higher than the device with indium tin oxide (ITO) anode. After applying the polystyrene nanosphere to form a photonic crystal array onto the device, the extracted light from organic mode can be further coupled out from device substrate mode. The overall luminous enhancement of the device with the combination of internal honeycomb metallic anode and external photonic crystal array is 115% higher than the traditional ITO-based OLED.

Using a layer-by-layer assembly method to fabricate a uniform and conductive nitrogen-doped graphene anode for indium-tin oxide-free organic light-emitting diodes.

Highly conductive, uniform, and transparent nitrogen-doped graphene multilayer films were produced by a layer-by-layer (LbL) assembly method. Such a technique was realized by alternate deposition of graphene oxide modified with the cationic surfactant N,N,N-trimethyl-1-dodecanaminium bromide (CTAB) and the anionic surfactant sodium dodecylbenzenesulfonate. In this way, we can achieve a highly conductive (900 S/cm), uniform, and controllable graphene film in terms of thickness, transmittance, and sheet resistance after high-temperature reduction. The improved conductivity is attributed to better graphitization and nitrogen-doping introduced by CTAB. The organic light-emitting diode using such a multilayer graphene film fabricated by the LbL method as an anode obtains higher current density and luminance at low voltage compared to that with an indium-tin oxide (ITO) anode. Moreover, the current efficiency of graphene-based device is comparable to that of an ITO-based device. It is proved that such a nitrogen-doped multilayer graphene film developed by the LbL assembly technique is a promising candidate for a transparent electrode in organic electronics.

Carrier injection efficiencies and energy level alignments of multilayer graphene anodes for organic light-emitting diodes with different hole injection layers

The carrier injection efficiencies of organic light-emitting diodes with a multilayer graphene (MLG) anode were compared for different hole injection layers (HIL). The energy level alignments at the hole injecting interface were also studied by using the ultraviolet photoelectron spectroscopy (UPS). We employed 1,1-bis[4-[N,N′-di(p-tolyl)amino]phenyl]cyclohexane (TAPC) as the hole transporting materials, while N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB) or 1,4,5,8,9,12-hexaaza-triphenylene-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) was used as the HIL. The current–voltage characteristics of hole-only devices showed that the MLG anode was only slightly inferior to the indium-tin oxide (ITO) anode in hole injection performance for all the HIL layers. The best efficiency was observed for both MLG and ITO anodes with HAT-CN HIL. We compared UPS-measured energy level alignment of TAPC/HIL/MLG interface for different HILs and concluded that the unique charge generation interface at TAPC/HAT-CN played a crucial role for the improved performance of HAT-CN HIL.

Highly efficient organic multi-junction solar cells with a thiophene based donor material

The efficiency of organic solar cells can be increased by serial stacked subcells even upon using the same absorber material. For the multi-junction devices presented here, we use the small molecule donor material DCV5T-Me. The subcell currents were matched by optical transfer matrix simulation, allowing an efficiency increase from 8.3% for a single junction up to 9.7% for a triple junction cell. The external quantum efficiency of the subcells, measured under appropriate light bias illumination, is spectrally shifted due to the microcavity of the complete stack, resulting in a broadband response and an increased cell current. The increase of the power conversion efficiency upon device stacking is even stronger for large area cells due to higher influence of the resistance of the indium tin oxide anode, emphasizing the advantage of multi-junction devices for large-area applications.

Superior performance of organic light-emitting diodes with microcavity effect

The electro-optics characteristics of organic light-emitting diodes (OLEDs) with microcavity effect were investigated. The transmittance of the substrate with Ag anode was lower than that of the indium-tin-oxide (ITO) anode due to the opaque characteristics of Ag. The current density of the device with Ag anode was high due to the low sheet resistance of Ag anode. The current efficiency of the device with Ag anode was high due to microcavity structure between Ag anode and Al cathode. Especially, the devices of Ag anode show over 43% higher current efficiency than that of conventional ITO anode. The low transmittance of Ag anode using microcavity effect realized as one kind of Fabry–Perot filters was also verified.

Improved performance of P3HT:PCBM solar cells by both anode modification and short-wavelength energy utilization using Tb(aca)3phen

The performance of P3HT:PCBM solar cells was improved by anode modification using spin-coated Tb(aca)3phen ultrathin films. The modification of the Tb(aca)3phen ultrathin film between the indium tin oxide (ITO) anode and the PE-DOT:PSS layer resulted in a maximum power conversion efficiency (PCE) of 2.99% compared to 2.66% for the reference device, which was due to the increase in the short-circuit current density (Jsc). The PCE improvement could be attributed to the short-wavelength energy utilization and the optimized morphology of the active layers. Tb(aca)3phen with its strong down-conversion luminescence properties is suitable for the P3HT:PCBM blend active layer, and the absorption region of the ternary blend films is extended into the near ultraviolet region. Furthermore, the crystallization and the surface morphology of P3HT:PCBM films were improved with the Tb(aca)3phen ultrathin film. The ultraviolent—visible absorption spectra, atomic force microscope (AFM), and X-ray diffraction (XRD) of the films were investigated. Both anode modification and short-wavelength energy utilization using Tb(aca)3phen in P3HT:PCBM solar cells led to about a 12% PCE increase.

Very high efficiency phosphorescent organic light-emitting devices by using rough indium tin oxide

The efficiency of organic light-emitting devices (OLEDs) is shown to significantly depend on the roughness of the indium tin oxide (ITO) anode. By using rougher ITO, light trapped in the ITO/organic wave-guided mode can be efficiently extracted, and a light outcoupling enhancement as high as 40% is achieved. Moreover, contrary to expectations, the lifetime of OLEDs is not affected by ITO roughness. Finally, an OLED employing rough ITO anode that exhibits a current efficiency of 56 cd/A at the remarkably high brightness of 105 cd/m2 is obtained. This represents the highest current efficiency at such high brightness to date for an OLED utilizing an ITO anode, without any external light outcoupling techniques. The results demonstrate the significant efficiency benefits of using ITO with higher roughness in OLEDs.

Enhancement of hole injection and electroluminescence by ordered Ag nanodot array on indium tin oxide anode in organic light emitting diode

We report the enhancement of hole injection and electroluminescence (EL) in an organic light emitting diode (OLED) with an ordered Ag nanodot array on indium-tin-oxide (ITO) anode. Until now, most researches have focused on the improved performance of OLEDs by plasmonic effects of metal nanoparticles due to the difficulty in fabricating metal nanodot arrays. A well-ordered Ag nanodot array is fabricated on the ITO anode of OLED using the nanoporous alumina as an evaporation mask. The OLED device with Ag nanodot arrays on the ITO anode shows higher current density and EL enhancement than the one without any nano-structure. These results suggest that the Ag nanodot array with the plasmonic effect has potential as one of attractive approaches to enhance the hole injection and EL in the application of the OLEDs.

Electrical properties of SAM-modified ITO surface using aromatic small molecules with double bond carboxylic acid groups for OLED applications

Abstract 5-[(3-Methylphenyl)(phenyl)amino]isophthalic acid (5-MePIFA) and 5-(diphenyl)amino]isophthalic acid (5-DPIFA) organic molecules were synthesized to form self-assembled monolayer on indium tin oxide (ITO) anode to enhance hole transport from ITO to organic hole transport layers such as TPD. The modified surface was characterized by scanning tunneling microscopy (STM). The change in the surface potential was measured by Kelvin probe force microscopy (KPFM). Our Kelvin probe force microscopy (KPFM) measurements showed that the surface potentials increased more than 100 mV with reference to bare indium tin-oxide. The results show that the threshold voltage on OLEDs with modified ITO is lowered significantly compared to OLEDs with unmodified ITO. The hole mobility of TPD has been estimated using space–charge-limited current measurements (SCLC).

Evaluation of algal biofilms on indium tin oxide (ITO) for use in biophotovoltaic platforms based on photosynthetic performance.

In photosynthesis, a very small amount of the solar energy absorbed is transformed into chemical energy, while the rest is wasted as heat and fluorescence. This excess energy can be harvested through biophotovoltaic platforms to generate electrical energy. In this study, algal biofilms formed on ITO anodes were investigated for use in the algal biophotovoltaic platforms. Sixteen algal strains, comprising local isolates and two diatoms obtained from the Culture Collection of Marine Phytoplankton (CCMP), USA, were screened and eight were selected based on the growth rate, biochemical composition and photosynthesis performance using suspension cultures. Differences in biofilm formation between the eight algal strains as well as their rapid light curve (RLC) generated using a pulse amplitude modulation (PAM) fluorometer, were examined. The RLC provides detailed information on the saturation characteristics of electron transport and overall photosynthetic performance of the algae. Four algal strains, belonging to the Cyanophyta (Cyanobacteria) Synechococcus elongatus (UMACC 105), Spirulina platensis. (UMACC 159) and the Chlorophyta Chlorella vulgaris (UMACC 051), and Chlorella sp. (UMACC 313) were finally selected for investigation using biophotovoltaic platforms. Based on power output per Chl-a content, the algae can be ranked as follows: Synechococcus elongatus (UMACC 105) (6.38×10−5 Wm−2/µgChl-a)>Chlorella vulgaris UMACC 051 (2.24×10−5 Wm−2/µgChl-a)>Chlorella sp.(UMACC 313) (1.43×10−5 Wm−2/µgChl-a)>Spirulina platensis (UMACC 159) (4.90×10−6 Wm−2/µgChl-a). Our study showed that local algal strains have potential for use in biophotovoltaic platforms due to their high photosynthetic performance, ability to produce biofilm and generation of electrical power.

Photolithographic patterning of PEDOT:PSS with a silver interlayer and its application in organic light emitting diodes

A patterning scheme for poly(3,4-ethylenedioxythio-phene):poly(styrenesulfonate) (PEDOT:PSS) is reported. With a silver interlayer, the conductive PEDOT:PSS film can be patterned down to micrometer scales by traditional photolithography, and this patterning scheme can be applied on large-area flexible substrates. Through systematical investigations, the patterning processes have no obvious influence on both the bulk and surface properties of PEDOT:PSS films. Efficient organic light emitting diodes (OLEDs) are realized based on this patterned PEDOT:PSS anode, and they show comparable performance to those devices with an indium tin oxide (ITO) anode. High-resolution OLED pixel arrays are also demonstrated. Our interlayer approach here has an advantage of patterning PEDOT:PSS with high resolution and large scale, and it is also compatible with traditional photolithographic processes which substantially save the capital cost. Results indicate that the photographically patterned conductive PEDOT:PSS film becomes a promising candidate for eletrical eletrode material in organic electronic applications.

Multi-color microfluidic electrochemiluminescence cells

We demonstrated multi-color microfluidic electrochemiluminescence (ECL) cells. 5,6,11,12-Tetraphenylnaphthacene (rubrene), 9,10-diphenylanthracene (DPA), tetraphenyldibenzoperiflanthene (DBP)-doped rubrene, and 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) dissolved in a mixed organic solvent of 1,2-dichlorobenzene and acetonitrile in the ratio of 2:1 (v/v) were used as yellow, blue, red, and green ECL solutions, respectively. Light emissions were confirmed using simple-structured ECL cells consisting of two indium tin oxide (ITO) coated glass substrates with an SU-8 spacer of thickness varying from 0.9 to 6μm. The SU-8-based microfluidic ECL cells were fabricated using photolithography and heterogeneous bonding techniques through the use of epoxy- and amine-terminated self-assembled monolayers. The emitting layers were formed on-demand by injecting the chosen ECL solutions into the microchannels sandwiched between ITO anode and cathode pairs. Multi-color ECL was successfully obtained at the light-emitting pixels. The microfluidic ECL cells with DBP-doped rubrene solution showed a maximum luminance of 11.6cd/m2 and the current efficiency of ca. 0.32cd/A at 8V. We expect that the proposed microfluidic device will be a highly promising technology for liquid-based light-emitting applications.

Improved performance of P3HT:PCBM photovoltaic devices with ITO treated by hydrogen peroxide.

The properties of poly(3-hexylthiophene):(6,6)-phenyl C61 butyric acid methyl ester (P3HT:PCBM) organic photovoltaic devices (OPVs) with indium tin oxide (ITO) anode treated by hydrogen peroxide are investigated. The optimized hydrogen peroxide solution has a concentration of 10% and ITO is treated for 15 min. The modification of ITO anode results in an enhancement of the power conversion efficiency (PCE) of the device, which is attributed to the increase of the photocurrent. The performance enhancement is attributed to the work function modification of the ITO substrate through the strong oxygenation of hydrogen peroxide, and then the charge collection efficiency is improved.

The role of Fe3O4 nanocrystal film in bilayer-heterojunction CuPc/C60 solar cells.

The CuPc/C60 thin-film bilayer-heterojunction solar cells are fabricated by vacuum deposition with bathocuproine (BCP) as the exciton-blocking layer. Ferroferric oxide (Fe3O4) nanocrystal film is inserted between the copper phthalocaynine (CuPc) layer and indium tin oxide (ITO) anode. The device performances dependent on the thickness of Fe3O4 are investigated and compared. The results show that both the short-circuit current density and fill factor are enhanced by introducing a 1 nm Fe3O4 buffer layer, leading to an increase of power conversion efficiency. The role of Fe3O4 as a buffer layer in the improvement of the device performances is studied in detail by ultraviolet photoemission spectroscopy (UPS).

Stability improvement of organic light emitting diodes by the insertion of hole injection materials on the indium tin oxide substrate

The degradation of organic light-emitting diodes (OLEDs) is a very complex issue, which might include interfacial charge accumulation, material diffusion, and electrical-induced chemical reaction during the operation. In this study, the origins of improvement in device stability from inserting a hole injection layer (HIL) at the indium tin oxide (ITO) anode are investigated. The results from aging single-layer devices show that leakage current increases in the case of ITO/hole transport layer contact, but this phenomenon can be prevented by inserting molybdenum oxide (MoO3) or 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN6) as an HIL. Moreover, X-ray photoemission spectroscopy suggests that the diffusion of indium atoms and active oxygen species can be impeded by introducing MoO3 or HAT-CN6 as an HIL. These results reveal that the degradation of OLEDs is related to indium and oxygen out-diffusion from the ITO substrates, and that the stability of OLEDs can be improved by impeding this diffusion with HILs.

Highly Responsive, Solution-Based Al/PbS and Au-Ti/PbS Schottky Photodiodes for SWIR Detection

We realized two PbS colloidal quantum dot (CQD) based Schottky photodetectors, formed of indium tin oxide anode, the photosensitive PbS layer, and a Schottky contacts of titanium-gold (Ti-Au) stack for higher longer lifetime and aluminum (Al) for higher responsivity. Long capping ligands of PbS QDs were replaced with shorter ones and layer-by-layer deposition method was applied to form pinhole-free and uniform PbS CQD films, enabling better responsivity and longer lifetime. In Al/PbS, under 2 V reverse bias and 5 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> illumination at 1550 nm, 0.195 A/W responsivity, 15.6% quantum efficiency, and 8.19 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> Jones normalized detectivity is achieved. In Au-Ti/PbS, under 3 V reverse bias and 5 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> illumination, 0.667 A/W responsivity, 53.3% quantum efficiency, and 2.12 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> Jones normalized detectivity is achieved.

Effect of oxygen plasma treatment on CdSe/CdZnS quantum-dot light-emitting diodes

Red-light-emitting diodes (LEDs) were fabricated using CdSe/CdZnS quantum dots (QDs). During the device fabrication process, the oxygen plasma treatment of the indium–tin oxide (ITO) surface was performed to improve the interfacial contact between the ITO anode and the hole injection layer. The device showed red emission at 622 nm, which was consistent with the dimensions of the QDs (band gap: 1.99 eV). The luminance was 108.77 cd/m2 and the current density was 230.2 mA/cm2 at an operating voltage of 7 V, when the oxygen plasma treatment was performed on the ITO surface. The luminance showed 207% improvement compared with that of LEDs fabricated without oxygen plasma treatment. These results suggested that the oxygen plasma treatment of the ITO surface improved the contact between ITO and PEDOT:PSS, and that the light emitting intensity was markedly improved.