Characterization of the Polarity Dependent Memory and Switching effect in sandwiches of metal/a-Si/ITO

The Polarity Dependent Memory and Switching effect (PDMS) has been observed in sandwiches of metal/a-Si/ITO layers and metal/a-Si/In. The film composition has been analysed by Auger Electron Spectroscopy and peak heights of the metals, Si and SiO_x have been measured as a function of film depth. No penetration of electrode material into the a-Si film was observed and the interfaces were abrupt even after many cycles of switching. A mechanism based on dendrite formation does not therefore operate in this type of PDMS. Traces of SiO_x have been found at the ITO/a-Si interface which are attributed to the presence of ITO or the deposition of In after exposure of a-Si to air. The SiO_x layer appears only in the OFF state and not in the ON state of the device. Hence a model based on voltage formation and destruction of an approximately 500 Å thick SiO_x layer at the a-Si/ITO interface is given.     

Fabrication of transparent conductive films with a sandwich structure composed of ITO/Cu/ITO

New transparent conductive films that had a sandwich structure composed of ITO/Cu/ITO multilayer films were prepared by a conventional RF and DC magnetron sputtering process on a polycarbonate substrate without intentional substrate heating. The thickness of each layer in the ITO/Cu/ITO films was kept constant at 50 nm/5 nm/45 nm. The optoelectrical and structural properties of the films were compared with conventional ITO single-layer films and ITO/Cu/ITO multilayered films. Although both films had identical thickness, 100 nm, the ITO/Cu/ITO films showed a lower resistivity, 3.5 × 10⁻⁴ Ω cm. In optical transmittance measurements, however, the ITO single-layer films showed a higher transmittance of 74% in the wavelength range of 300-800 nm. XRD spectra showed that both the ITO and ITO/Cu/ITO films were amorphous. The figure of merit, φ_TC, reached a maximum of 5.2 × 10⁻⁴ Ω⁻¹ for the ITO/Cu/ITO films, which was higher than the φ_TC of the ITO films (1.6 × 10⁻⁴ Ω⁻¹). The φ_TC results suggested that ITO/Cu/ITO films had better optoelectrical properties than conventional ITO single-layer films.     

Effect of SiO2 buffer layer thickness on the properties of ITO/Cu/ITO multilayer films deposited on polyethylene terephthalate substrates

Transparent conductive ITO/Cu/ITO films were deposited on polyethylene terephthalate (PET) substrates with a SiO₂ buffer layer by magnetron sputtering using three cathodes at room temperature. The effect of the SiO₂ buffer layer thickness on the electrical and optical properties of ITO/Cu/ITO films was investigated. The ITO/Cu/ITO film deposited on the 40 nm thick SiO₂ buffer layer exhibits a sheet resistance of 143Ω/sq and transmittance of 65% at 550 nm wavelength. Highly transparent ITO/Cu/ITO films with a transmittance of 80% and a sheet resistance of 98.7Ω/sq have been obtained by applying −60 V substrate bias.     

Effect of SiO2 buffer layer thickness on the properties of ITO/Cu/ITO multilayer films deposited on polyethylene terephthalate substrates

Transparent conductive ITO/Cu/ITO films were deposited on polyethylene terephthalate (PET) substrates with a SiO₂ buffer layer by magnetron sputtering using three cathodes at room temperature. The effect of the SiO₂ buffer layer thickness on the electrical and optical properties of ITO/Cu/ITO films was investigated. The ITO/Cu/ITO film deposited on the 40 nm thick SiO₂ buffer layer exhibits a sheet resistance of 143Ω/sq and transmittance of 65% at 550 nm wavelength. Highly transparent ITO/Cu/ITO films with a transmittance of 80% and a sheet resistance of 98.7Ω/sq have been obtained by applying −60 V substrate bias.     

Effects of (NH4)2Sx treatment on the electrical and optical properties of indium tin oxide/conducting polymer electrodes

In this study, the effects of (NH₄)₂S_x treatment on the electrical and optical properties of the indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) electrodes were researched. The authors found that (NH₄)₂S_x treatment could result in suppressing the hysteresis-type current-voltage characteristics related to the interfacial capacitance variation and a reduction in the equivalent refractive index of the ITO/PEDOT:PSS electrodes, owing to the improvement in the interfacial stability of the ITO/PEDOT:PSS electrodes and a reduction in the interface trap-states related charge store at the ITO/PEDOT:PSS interface. This implies that the ITO/PEDOT:PSS electrodes fabricated using the (NH₄)₂S_x-treated ITO may produce a higher extraction efficiency for ITO/PEDOT:PSS-based optoelectronic devices.     

The structure and composition of Te/CdS thin film diodes

The composition and crystal structure of the interfacial region in thin film Te/CdS heterojunctions were investigated using Auger electron spectroscopy and reflection electron diffraction. The junction region is found to contain a thi CdTe layer accompanied by a graded layer of composition CdTe_xS_1−x.     

Reductive ion insertion into thin-film indium tin oxide (ITO) in aqueous acidic solutions: the effect of leaching of indium from the ITO

The etching of indium-tin oxide (ITO) in acidic solution has been investigated electro-chemically via conductivity change, cyclic voltammetry and in situ UV-visible spectroscopy. It is seen that the ITO has a new color and lower conductivity when reduced. Proton insertion is faster than proton extraction, with D=7.0×10^-11 cm² s^-1 and 2.4×10^-11 cm² s^-1 respectively. Spectroscopic and kinetic results are discussed in terms of a possible mixed-valent solid-state material comprising In(I)–In(III) oxides, although it is concluded that such a system does not, in fact, exist. It is shown that the chemical reactivity of reduced ITO is more-or-less the same as the oxidized material, but the observed changes result from a decreased mechanical strength causing H_xITO to disintegrate faster than ITO. Implications are discussed for ITO-based devices that contain traces of aqueous acid.     

A three-dimensional electrode for photoelectrochemical cell: TiO2 coated ITO mesoporous film

In this letter, TiO₂ coated ITO mesoporous film was prepared by dipping doctor-blade ITO mesoporous film in TiO₂ sol, followed by sintering at 500 °C for 30 min. The CdS quantum dots (QDs) were deposited on TiO₂ coated ITO mesoporous film using sequential chemical bath deposition (S-CBD) method to form a three-dimensional (3D) electrode. The photo-activity of ITO mesoporous film/TiO₂/CdS electrode was investigated by forming a photoelectrochemical cell, which indicated that the ITO mesoporous film/TiO₂/CdS electrode was efficient in photoelectrochemical cell as a working electrode. The 3D electrode showed lower performance than the conventional electrode of TiO₂ mesoporous film/CdS, and more works are needed to improve the performance of 3D electrode.     

Formation, sintering, and electrical conductivity of (Nd1−xCax)CrO3 (0≤x≤0.25) using citric acid as a gelling agent

In Ca²⁺-substituted NdCrO₃, single-phase perovskite compounds (Nd_1−xCa_x)CrO₃, where x=0-0.25, have been formed by a citric acid processing. (Nd_1−xCa_x)CrO₃ powders consisting of submicrometer-size particles are sinterable; dense materials can be fabricated by sintering for 2 h at 1700°C under atmospheric pressure. The relative densities, grain sizes, and electrical conductivities increase with increased Ca²⁺ content. (Nd_0.75Ca_0.25)CrO₃ materials show an excellent electrical conductivity of 1.9×10 S m⁻¹ at 1000°C.     

Large phase-transition hysteresis for nanostructured VOx film prepared on ITO conductive glass by DC reactive magnetron sputtering

Nanostructured vanadium oxide (nano-VO_x) films were prepared on indium-tin oxide (ITO) glass substrate at low temperature by means of direct current (DC) reactive magnetron sputtering from pure vanadium target in Ar + O₂ atmosphere. Field emission scanning electron microscope (SEM) reveals that the VO_x film is composed of spheroidal nanoparticles whose diameters are in the range of 20–40 nm. This nano-VO_x film shows a broad hysteresis loop whose width is as large as 41.6 °C. Moreover, the metal-insulator transition (MIT) can also be triggered by Joule heat produced by electrical current through the ITO sublayer. Compared to traditional heating of the sample by heating plate, this Joule heating is more efficient and convenient, which enables potential applications of this nano-VO_x film on ITO conductive glass in compact storage devices.     

Phase control of CuxTe film and its effects on CdS/CdTe solar cell

Phase control is critical for achieving high-performance CdTe cells when Cu_xTe is used as a back-contact for CdTe cells. Cu_xTe phases are mainly controlled by the Cu/Te ratio, and they can also be affected by post-heat-treatment temperature. Although Cu₂Te has the highest conductivity, it is unstable and provides more Cu diffusion into the CdS and CdTe films. Cu diffusion into the CdS causes “cross-over”, and Cu diffusion into the CdTe film creates Cu-related defects that lower photogenerated carrier lifetime and result in voltage-dependent collection. A “recontact” experiment clearly indicated that the mechanism giving rise to “roll-over” is the formation of Cu-related oxides, rather than the loss of Cu on the back-contact.     

Conductive polymer PEDOT:PSS back contact for CdTe solar cell

Two types of superstrate glass/ITO/CdS/CdTe PV structures were prepared by high vacuum evaporation technique with (i) activation of CdS layer and CdS/CdTe bi-layer structure step-by-step and (ii) activation of CdS/CdTe bi-layer structure. The activation was performed by annealing the structures with CdCl₂ in air at 400 °C for 15 min. Main conditions for CdS and CdTe thin films deposition and following treatment were selected from the literature data with the purpose to prepare and compare complete CdTe solar cells with standard p + Cu_xTe back contact and conductive polymer poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (PEDOT:PSS) back contact. Obtained layers and structures were characterized using the XRD, SEM and I-V methods. Both the methods of activation treatment give comparable results from the point of view PV properties of complete solar cells. It was found that highly conductive PEDOT:PSS intermediate layer can significantly improve the back contact characteristics of CdTe. However these hybrid structures need to be further optimized to compete successfully with conventional inorganic back contacts in complete CdTe solar cells.     

FeNi3/indium tin oxide (ITO) composite nanoparticles with excellent microwave absorption performance and low infrared emissivity

FeNi₃/indium tin oxide (ITO) composite nanoparticles were synthesized by a self-catalyzed reduction method and a sol–gel process. The dependence of the content of ITO phase with the mole ratios of In:Sn of different sols was investigated. The relation between the electrical conductivity, infrared emissivity of FeNi₃/ITO composite nanoparticles and the content of ITO phase was discussed. Electromagnetic wave absorption (EMA) performance of products was evaluated by using transmission line theory. It was found that EMA performance including the intensity and the location of effective band is significantly dependent on the content of ITO phase. The low infrared emissivity and superior EMA performance of FeNi₃/ITO composite nanoparticles can be both achieved when the mole ratio of In:Sn in sol is 9:1.     

Interface modification of ITO thin films: organic photovoltaic cells

In this paper we review our recent studies of the surface characterization of commercially available indium-tin-oxide (ITO) thin films, using photoelectron spectroscopies (XPS and UPS) and electrochemistry of chemisorbed probe molecules such as ferrocene dicarboxylic acid (Fc(COOH)₂). The modification of these ITO films through chemisorption of carboxylic acid-substituted small molecules, such as Fc(COOH)₂, 3-thiophene acetic acid (3-TAA), and the subsequent modification of these interfaces with electrochemically grown conducting polymer (CP) films is also introduced. We report preliminary results of our studies changes in performance of vacuum deposited organic photovoltaic (PV) cells as a result of these ITO substrate modification steps. The surfaces of as-received ITO films, and those cleaned by various solution and plasma-etching processes, are unavoidably hydrolyzed to In(OH)₃-like and InOOH-like surface species, which leaves the ITO surface with at most 40-50% of the electronically active sites available for electron transfer reactions. Modification of the ITO surface with electroactive small molecules such as Fc(COOH)₂ and 3-TAA provides for better wettability of organic layers to the polar ITO surface and enhanced electrical contact (lower series resistance, R_S) between the ITO anode, spin-cast or electrodeposited PEDOT:PSS layers and copper phthalocyanine (CuPc) layers in multilayer (CuPc/C₆₀/BCP) excitonic PV cells. Improvements in PV J/V (current/voltage) responses are noted mainly through increases in short-circuit photocurrent and lowered series resistances (R_S) when electroactive small molecules are chemisorbed to the ITO surface, prior to spin-casting of conducting polymer, PEDOT:PSS, layers.     

Microstructural,electrical and optical properties of indium tin oxide (ITO) nanoparticles synthesized by co-precipitation method

In the present study, the synthesis of Tin doped indium oxide (ITO) nanopowder at different compositions (In/Sn = 0, 5, 10, 15 at %) was carried out by co-precipitation method. The decomposition of precipitated indium tin acetylacetonate precursor to form In₂O₃–SnO₂ (Sn_1?xIn_xO₂) at 400 °C was confirmed by the thermal and FTIR studies. The changes in strain and grain size of the synthesized particle with respect to dopant concentration were determined from the X-ray diffraction (XRD) analysis. Transmission electron microscopy (TEM) images support to confirm the grain size. The optical properties on ITO nanoparticles were analyzed with UV–visible spectroscopy, and band gap was found to vary from 3.62 to 3.89 eV with Sn dopant concentration. This variation was ascribed to the quantum confinement effect.     

Structural studies of the (La,Sr) CrO3 system

Phase relationships in the La_1?xSr_xCrO₃ (0.25 ≤ x ≤ 0) system have been investigated. Substitution of Sr into LaCrO₃ leads to a phase region with rhombohedral symmetry at room temperature which is oxygen-deficient under strongly reducing conditions. The orthorhombic structure of LaCrO₃ and the rhombohedral structure of La_0.75Sr_0.25CrO₃ have been refined by profile fitting of neutron powder diffraction data.     

Study of composition reproducibility of electrochemically co-deposited CuInSe2 films onto ITO

CuInSe₂ thin films were electrodeposited onto ITO substrates from aqueous solution containing 4.5 mM CuSO₄, 10 mM In₂(SO₄)₃ and 10 mM SeO₂ isopotentionally and by two-step deposition technique — changing the deposition potential during the deposition process step-wise: from lower to higher and vice versa in the potential range of − 0.6 to − 1.0 V (vs. Ag/AgCl). Solution pH was varied from 1.3 to 1.9 at temperatures 293 and 313 K to clarify the region for co-deposition of In-rich CuInSe₂ films on ITO with high composition reproducibility. Morphology and composition of CuInSe₂ layers depended not only on deposition temperature and potential, but also on the direction of potential change in the case of two-step process. The potential change from lower negative values to higher ones resulted in layers with low adhesivity. Alternatively, from higher potential to lower potential, the homogeneous, well-structured, adhesive and smooth layers were deposited. Modifying deposition periods in a two-step process, the chemical composition of films can be tailored. At pH < 1.9 reproducibility of the film's composition was low. ITO electrodes were found not to be stable at pH < 1.9.     

Effect of iodine doping of phthalocyanine on the photocurrent generation in a phthalocyanine/C60 heterojunction

Photocurrent generation in an indium-tin oxide (ITO)/iodine-doped Ni-phthalocyanine (NiPc-I_x)/C₆₀/In/Al heterojunction device with x ~ 1 was studied. By keeping the device in air after preparation, the device slowly reached a stationary state in which the sign of the photocurrent is opposite to that of a non-doped ITO/NiPc/C₆₀/In/Al device although the rectification direction for the dark current is the same. By a simulation of incident photon-to-current conversion efficiency spectra and a measurement of internal electric field by electroabsorption spectroscopy, it was elucidated that, in the doped device, the band bending near the phthalocyanine/C₆₀ interface is absent and the photocurrent is generated by a weak Schottky barrier at the C₆₀/In interface. It is also shown that the C₆₀ film encapsulates the doped iodine into the NiPc-I_x layer to stabilize the doping level and prevent the reaction of iodine with In.     

The formation of different phases of CuxTe and their effects on CdTe/CdS solar cells

Material studies and device applications of Cu_xTe in an NREL-developed CdTe solar cell structured as glass/Cd₂SnO₄/ZnSnO_x/CdS/CdTe are presented. The Cu_xTe primary back contact was formed by evaporating a Cu layer with various thicknesses at room temperature on HNO₃/H₃PO₄ (NP) solution etched CdTe layer. A post-annealing was then followed. The structural evolution and electrical properties of Cu_xTe were investigated. Cu/Te ratio and post-annealing temperature are two processing parameters in this study. The Cu_xTe phases are mainly controlled by the Cu/Te ratio. After a post-annealing at a low temperature, such as 100 °C, no Cu_xTe phase transformation from its as-deposited phase was observed. A post-annealing treatment at a higher temperature, such as 250 °C, can reveal the stoichiometric Cu_xTe phases based on the Cu/Te ratio used in the devices. But a post-annealing at a further higher temperature, such as 400 °C, resulted in a complicated Cu_xTe phase appearance. CuTe, Cu_1.4Te, and Cu₂Te are three major phases detected by X-ray diffraction (XRD) for different Cu thickness application annealed at 250 °C. Application of Cu thicker than 60 nm degrades open-circuit voltage (V_oc) and shunting resistance (R_sh), but increases series resistance (R_s). The correlation between device performance and the Cu_xTe back contact illustrates that the process used for forming the Cu₂Te back contact failed to produce good fill factor (FF) and also introduced higher barrier height. The best device was observed for a back contact with a mixed Cu_1.4Te and CuTe phases.     

Infinitely high etch selectivity during CH4/H2/Ar inductively coupled plasma (ICP) etching of indium tin oxide (ITO) with photoresist mask

Under certain conditions during ITO etching using CH₄/H₂/Ar inductively coupled plasmas, the etch rate selectivity of ITO to photoresist (PR) was infinitely high because the ITO films continued to be etched, but a net deposition of the α-C:H layer occurred on the top of the PR. Analyses of plasmas and etched ITO surfaces suggested that the continued consumption of the carbon and hydrogen in the deposited α-C:H layer by their chemical reaction with In and Sn atoms in the ITO resulting in the generation of volatile metal-organic etch products and by the ion-enhanced removal of the α-C:H layer presumably play important roles in determining the ITO etch rate and selectivity.