Indium Tin Oxide Anode Research Articles

Platinum nanoparticles modified indium tin oxide anodes for enhancing the efficiency and stability of organic solar cells

Organic P3HT:PCBM heterojunction solar cells with indium tin oxide (ITO) anodes modified by platinum nanoparticles (NPs) were fabricated. The open-circuit voltage (Voc) of the cells was increased compared with the reference cell without Pt NPs. An enhanced power conversion efficiency of ∼12% was obtained for the optimum sputtering deposition duration of 10s. A double junction model of the Schottky junction and the p–n junction is proposed to describe the frequency dependence of the capacitance in the modified cell. The formation of the front Schottky junction allows efficient collection of holes from the active layer, and enhances the Voc. Moreover, the air stability of organic solar cells was improved. The modification of ITO with Pt NPs shows promise as a technique for fabrication of high-efficiency stable photovoltaic devices.

The effects of tris(2-phenylpyridine) iridium on the hole injection and transport properties of 4,4′,4″-tri(N-carbazolyl)-triphenylamine thin films

The effects of tris(2-phenylpyridine) iridium [Ir(ppy)3] on the hole injection and transport properties of 4,4′,4″-tri(N-carbazolyl)-triphenylamine (TCTA) thin films have been investigated by current–voltage characteristic and admittance spectroscopy measurement. Dramatically improved hole injection can be achieved by inserting either pure Ir(ppy)3 or Ir(ppy)3 doped TCTA film between the indium–tin-oxide anode and TCTA layer, because of the hole transport ability and relatively higher-lying highest occupied molecular orbital (HOMO) level of Ir(ppy)3. When doping Ir(ppy)3 into TCTA, it acts as a role of trapping center and greatly reduces the hole mobility. Also, the hole transport properties in TCTA:Ir(ppy)3 thin films are greatly affected by doping concentration and show a nontrivial fluctuant dependence on the doping concentration. The origin of such dependence is discussed. This study provides insight into determining the charge carrier mobility of phosphorescent material doped organic semiconductor film.

Systemic Studies of Tetraphenylethene–Triphenylamine Oligomers and a Polymer: Achieving Both Efficient Solid‐State Emissions and Hole‐Transporting Capability

By employing a new synthetic strategy, a series of oligomers and a polymer composed of different number of tetraphenylethene and triphenylamine units was designed and synthesised. The optical physics properties and electroluminescence behaviours were studied comparatively. All the molecules demonstrate an aggregation-induced emission (AIE) phenomenon and bear very high quantum yields in the solid state. The emission wavelengths and quantum efficiencies alternate with the change of the molecular configurations and achieve their maximum at the largest oligomer. The thermal stabilities also become higher along with the increase in the molecular weight. The molecules have suitable HOMO levels that match the work function of the indium tin oxide (ITO) anode. They can act as both light-emitting and hole-transporting materials in OLEDs. Thus the present strategy combines the intrinsic emissive nature of AIE materials and the good hole-transport capability of aromatic amines, thereby achieving a win-win for both optical and electrical properties.

Efficient and reliable green organic light-emitting diodes with Cl2 plasma-etched indium tin oxide anode

The effects of brief etching with Cl2-based inductively coupled plasma (ICP) on the surface chemistry and properties of indium-tin-oxide (ITO) were investigated. Due to the low volatility of InClx, Cl2, and Cl2/BCl3 ICP etching created stable In-Cl polar bonds at the ITO surfaces, raising its work function by up to 1.0 eV. Green phosphorescent organic light-emitting diodes (OLEDs) built on ICP-etched ITO/glass substrates exhibited a brightness of 1.4 × 104 cd/m2 and a current efficiency of 70 cd/A at 20 mA/cm2, which were 40% higher than those of similar OLEDs with an O2 plasma-treated ITO anode. The OLEDs with plasma chlorinated ITO also showed better stability and reliability. These results suggest that brief chlorine plasma etching can result in stable chlorinated ITO surfaces with a high work function, leading to more balanced charge injection and performance enhancement of OLEDs.

Flexible Top-Emitting Organic Light-Emitting Diodes Using Semi-Transparent Multi-Metal Layers

In this paper, the improved device performance of top-emitting organic light-emitting diodes (TEOLEDs) with a thin multi-metal layer stack of nickel/silver/nickel (Ni/Ag/Ni) and aluminum/silver/aluminum (Al/Ag/Al) that were used as the anode and cathode on a flexible substrate is discussed. In particular, Indium-Tin-Oxide (ITO) as an anode electrode has been used recently even though it has some problems for flexible devices. Therefore we suggested that a thin multi-metal layer electrode as a new anode is fabricated instead of ITO anode. It was verified that the ITO-free TEOLEDs showed an enhanced probability of the recombination of the electrons and holes through an improved electron/hole charge balance. We also analyzed the optical and electrical characteristics using the current density, luminance, luminance efficiency, external quantum efficiency (EQE), CIE x, y coordinates, and EL spectra of flexible TEOLED devices were characterized. ITO-free, flexible, green-emitting OLEDs with a low cost and a simple process were demonstrated.

Hole Injection Enhancements of a CoPc and CoPc:NPB Mixed Layer in Organic Light-Emitting Devices

The hole injection enhancement in organic light-emitting devices with the insertion of a cobalt phthalocyanine (CoPc) hole injection layer (HIL) between the indium tin oxide (ITO) anode and the N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) hole transport layer (HTL) was demonstrated through current density–voltage–luminance measurements, in situ photoelectron spectroscopy experiments, and theoretical calculations. The CoPc HIL significantly reduces the hole injection barrier (HIB) and thus serves as an efficient HIL like the conventional copper phthalocyanine HIL. This commonality originates from their similar configurations of the highest occupied molecular orbital (HOMO), which consists of conducting macrocycle isoindole ligands, not related to the central metal. However, as the CoPc:NPB mixed HIL is inserted, the hole injection enhancements are inferior to that of a single CoPc HIL. This is due to the electron transfer from NPB to CoPc, which pulls the HOMO level of the mixed HIL ...

Improving efficiency of organic light-emitting diodes fabricated utilizing AZO/Ag/AZO multilayer electrode

Multilayer transparent electrode based on Al-doped zinc oxide (AZO)/Ag/Al-doped zinc oxide (AZO) was fabricated by sputtering, and a green organic light-emitting diode (OLED) device utilizing AZO/Ag/AZO as anode was fabricated. The AZO/Ag/AZO multilayer film exhibited superior square resistance and optical transmittance to those of commercial indium tin oxide (ITO). In comparison with the green OLEDs based on ITO and pure AZO anode, the green OLED based on AZO/Ag/AZO showed the highest light-emitting efficiency. The results indicate that AZO/Ag/AZO multilayer electrodes are a promising low-cost, low-toxic and low-temperature processing electrode scheme for OLED application.

Nonvolatile organic write-once-read-many-times memory devices based on hexadecafluoro-copper-phthalocyanine

Nonvolatile organic write-once-read-many-times memory device was demonstrated based on hexadecafluoro-copper-phthalocyanine (F16CuPc) single layer sandwiched between indium tin oxide (ITO) anode and Al cathode. The as fabricated device remains in ON state and it can be tuned to OFF state by applying a reverse bias. The ON/OFF current ratio of the device can reach up to 2.3 × 103. Simultaneously, the device shows long-term storage stability and long retention time in air. The ON/OFF transition is attributed to the formation and destruction of the interfacial dipole layer in the ITO/F16CuPc interface, and such a mechanism is different from previously reported ones.

Stability enhancement of organic solar cells with solution-processed nickel oxide thin films as hole transport layers

AbstractOne of the main causes of the degradation of organic solar cells is the interface between the indium tin oxide (ITO) anode and the poly (3,4-ethylendioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) hole transport layer (HTL), which is known to be unstable. On the contact surface, corrosion of the ITO is induced by PEDOT:PSS, and this degrades the performance of the device. In this paper, we solve this problem by introducing an inorganic HTL, nickel oxide (NiO), between the ITO and the active layer. Solution process, a low-cost production method for preparing thin films, is employed to fabricate the NiO HTL for organic solar cells based on poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM). The performance of the resulting organic solar cells is optimized by modifying the baking conditions of the NiO thin films, yielding a power conversion efficiency enhancement of 1.97% and fill factor of 52.11%. Moreover, a remarkable improvement in cell lifetime is observed. X-ray photoelectron spectroscopy studies show that cell performance and stability strongly depend on the oxygen composition ratio of the NiO structure. The transition of the O2− ratio is a key factor that determines the conductivity of NiO. These results compare favorably with those reported in the literature for conventional devices with PEDOT:PSS.

Thin air-plasma-treated alkali fluoride layers for improved hole extraction in copper <inline-formula><math display="inline" overflow="scroll"><mrow><mtext>phthalocyanine</mtext><mo>/</mo><msub><mrow><mi mathvariant="normal">C</mi></mrow><mrow><mn>70</mn></mrow></msub></mrow></math></inline-formula>-based solar cells

Alkali fluorides, mostly LiF and CsF, are well-known to improve electron injection/extraction in organic light-emitting diodes (OLEDs) and organic solar cells (OSCs). They are also utilized, though to a lesser extent, for hole injection in OLEDs. Here we demonstrate a new role for such fluorides in enhancing OSCs' hole extraction. We show that an ultrathin air-plasma-treated alkali fluoride layer between the indium tin oxide (ITO) anode and the active layer in copper phthalocyanine (CuPc)/C70-based OSCs increases the short circuit current by up to ∼ 17% for cells with LiF and ∼ 7% for cells with NaF or CsF. The effects of the fluoride layer thickness and treatment duration were evaluated, as were OSCs with oxidized and plasma-treated Li and UV-ozone treated LiF. Measurements included current voltage, absorption, external quantum efficiency (EQE), atomic force microscopy, and x-ray photoelectron spectroscopy, which showed the presence of alkali atoms F and O at the treated ITO/fluoride surface. The EQE of optimized devices with LiF increased at wavelengths >560 nm, exceeding the absorption increase. Overall, the results indicate that the improved performance is due largely to enhanced hole extraction, possibly related to improved energy-level alignment at the fluorinated ITO/CuPc interface, reduced OSC series resistance, and in the case of LiF, improved absorption.

Properties of Interface between Organic Hole-Transporting Layer and Indium Tin Oxide Anode Modified by Fluorinated Self-Assembled Monolayer

Properties of Interface between Organic Hole-Transporting Layer and Indium Tin Oxide Anode Modified by Fluorinated Self-Assembled Monolayer

Properties of Interface between Organic Hole-Transporting Layer and Indium Tin Oxide Anode Modified by Fluorinated Self-Assembled Monolayer

The electronic structure and chemical properties of the interface between indium tin oxide (ITO) modified by a fluorinated self-assembled monolayer (F-SAM) and a N,N '-bis(1-naphthyl)-N,N '-diphenyl-1,1'-diphenyl-1,4'-diamine (α-NPD) layer were investigated in order to clarify the effects of the F-SAM modification of ITO anodes on the driving voltage and lifetime of organic light-emitting diodes (OLEDs). Ultraviolet and X-ray photoelectron spectroscopy revealed that the F-SAM modification of ITO led to a shallower highest occupied molecular orbital level in the α-NPD layer near the interface than in conventionally treated ITO, a chemical reaction between F-SAM and α-NPD, and the migration of adsorbed fluorine into the α-NPD layer. These results indicate that high conductance, the suppression of crystallization, and the inhibition of oxidation in the hole-transporting layer along with a small hole-injection barrier height at the anode/HTL interface contribute to the excellent properties of OLEDs having ITO anodes modified by F-SAM.

Extremely efficient flexible organic light-emitting diodes with modified graphene anode

By replacing conventional indium tin oxide (ITO) anodes with high-work-function, low-sheet-resistance graphene anodes, researchers demonstrate flexible fluorescent organic LEDs with extremely high luminous efficiencies of 37.2 lm W–1 for fluorescent devices and 102.7 lm W–1 for phosphorescent devices. These values are significantly higher than those of optimized organic LEDs based on ITO anodes.

PbS Colloidal Quantum Dot Photodiodes for SWIR Detection

In this work, PbS colloidal quantum dot based photodiodes are realized compatible for the integration on ROIC's. Schottky photodiode architecture is selected for its fast response and moderate sensitivity. The device is formed from Indium tin oxide (ITO) anode, the photosensitive PbS layer and a schottky contact formed of titanium and gold. Pinhole-free uniform PbS quantum dots film achieved by optimized layer by layer spin coating process. Solid-state ligand change procedure applied during film coating using 3-mercaptopropionic acid (3-MPA) in order to remove long oleic acid ligand that degrades electron mobility in the film. Fabricated detectors achieved rectification ratios of 15 at +/- 1 V bias. Preliminary tests show a responsivity of 0.24 A/W is achieved. Specific detectivity D* is calculated as 3,54x1010 that is limited due to high dark currents.

Fluorinated alkyl phosphonic acid SAMs replace PEDOT:PSS in polymer semiconductor devices

Fluorinated phosphonic acids were self-assembled to form monolayers (SAMs) on indium tin oxide anodes, resulting in work functions that are 0.15–0.4eV larger than PEDOT:PSS by Kelvin probe. X-ray photoelectron spectroscopy and water contact angle measurements were used to study monolayer growth kinetics and to verify the degree of coverage. Hole-only devices and white polymer light emitting diodes were constructed using unmodified ITO, SAM-modified ITO, and PEDOT:PSS on ITO to investigate the influence of the fluorinated SAMs on hole injection. Hole-only devices indicate improved hole injection compared to PEDOT:PSS. Compared with light-emitting diodes using pure ITO anodes, the SAM-modified devices show improved charge injection and ten times higher luminous efficiency. Compared to devices using PEDOT:PSS, SAM-modified devices show improved brightness and luminous efficiency, although with a slightly larger turn-on voltage. These materials are therefore suitable candidates to replace PEDOT:PSS as a hole injection layer in PLEDs.

Long-lasting flexible organic solar cells stored and tested entirely in air

We report on improved stability of poly(3-hexylthiopene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester bulk heterojunction solar cells using an indium tin oxide (ITO) anode and an indium metal cathode. Except for the ITO anode the devices are fabricated, stored, and tested entirely in air without encapsulation, exhibiting less than 10% loss in power conversion efficiency after 200 days. X-ray photoelectron spectroscopy shows that this improvement in ambient stability is correlated with the diffusion of indium from the cathode into the active polymer. The In oxidizes presumably resulting in a reduction in P3HT polymer chain degradation.

‘Giant’ CdSe/CdS Core/Shell Nanocrystal Quantum Dots As Efficient Electroluminescent Materials: Strong Influence of Shell Thickness on Light-Emitting Diode Performance

We use a simple device architecture based on a poly(3,4-ethylendioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-coated indium tin oxide anode and a LiF/Al cathode to assess the effects of shell thickness on the properties of light-emitting diodes (LEDs) comprising CdSe/CdS core/shell nanocrystal quantum dots (NQDs) as the emitting layer. Specifically, we are interested in determining whether LEDs based on thick-shell nanocrystals, so-called "giant" NQDs, afford enhanced performance compared to their counterparts incorporating thin-shell systems. We observe significant improvements in device performance as a function of increasing shell thickness. While the turn-on voltage remains approximately constant for all shell thicknesses (from 4 to 16 CdS monolayers), external quantum efficiency and maximum luminance are found to be about one order of magnitude higher for thicker shell nanocrystals (≥13 CdS monolayers) compared to thinner shell structures (<9 CdS monolayers). The thickest-shell nanocrystals (16 monolayers of CdS) afforded an external quantum efficiency and luminance of 0.17% and 2000 Cd/m(2), respectively, with a remarkably low turn-on voltage of ~3.0 V.

Study on the Panel Fabrication for the Field Emission Display with Symmetrical Electrode Stripe

Using carbon nanotubes as cold cathode material, the panel fabrication for the diode field emission display (FED) with symmetrical electrode stripe was studied. The indium tin oxide (ITO) film was used as conduction electrode on the substrate plate surface, and the precise photolithography method was adopted as the high effective fabrication process. For the both cathode and anode plate, the whole ITO film would be etched in the bar form, and the divided bar ITO stripe would be arranged symmetrically. On the cathode plate surface, the printed silver slurry was used to form the cathode extension lines and the cathode insulation layer was formed with the sintered insulation slurry. Whether for the cathode ITO electrodes or for the anode ITO electrodes, the length of bar ITO electrode become small, which would be beneficial for reducing the panel working-voltage. The FED panel was sealed and measured, which possessed good field emission characteristics.

On the ultrathin gold film used as buffer layer at the transparent conductive anode/organic electron donor interface

Previously, we have shown that a gold thin film of only 0.5 nm introduced at the interface between the indium tin oxide or ZnO anode and the organic electron donor in organic photovoltaic cells induces a strong improvement of the cell efficiency. Of course a thickness of 0.5 nm corresponds only to an averaged thickness, the films being too thin to be continuous. For a clear understanding of the physical mechanisms that are responsible for this improved behaviour, it is important to know the fractional coverage and the island height of this thin Au film. In the present work, we have used two different techniques, such as treated scanning electron microscope images and analysis of the inelastic part of peaks of X-ray photoelectron spectroscopy spectra, to estimate the gold coverage and island height of the transparent conductive anode. There is an excellent agreement between the results achieved by both methods. Only 15% of the anode is covered, which proves the high efficiency of gold as an anode buffer layer in organic photovoltaic devices.

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.