Highly transparent Ag doped In2O3 electrodes with high work function for organic solar cells

We report highly transparent Ag-doped In₂O₃ (IAO) films with high work function for use as transparent anodes in organic solar cells (OSCs). The electrical, optical, structural, and morphological properties of IAO films and their work function were investigated as a function of the rapid thermal annealing (RTA) temperature. At an RTA temperature of 600 °C, the IAO film showed a sheet resistance of 23.12 Ohm/square, an optical transmittance of 79.28%, and a work function of 5.21 eV, similar to conventional Sn-doped In₂O₃ (ITO) films. The low resistivity of the IAO film was closely related to oxygen vacancies caused by Ag suboxide formation in the In₂O₃ matrix. A bulk-heterojunction OSC with the optimized IAO anode showed performance comparable to that of an OSC with a reference ITO anode, indicating that the IAO films is a promising anode material for use in OSCs.     

Enhanced acetone gas sensing performance of the multiple-networked Fe2O3-functionalized In2O3 nanowire sensor

In₂O₃ nanowires functionalized with Fe₂O₃ nanoparticles were synthesized by the thermal evaporation of In₂S₃ powders in an oxidizing atmosphere followed by the solvothermal deposition of Fe₂O₃ and their acetone gas sensing properties were examined. The pristine and Fe₂O₃-functionalized In₂O₃ nanowires exhibited responses of 141–390% and 298–960%, respectively, to 10–500 ppm acetone at 200 °C. The Fe₂O₃-functionalized In₂O₃ nanowire sensor showed stronger electrical response to acetone gas at 200 °C than the pristine In₂O₃ nanowire counterpart. The former showed more rapid response but slower recovery than the latter. Both the pristine and Fe₂O₃-functionalized In₂O₃ nanowire sensors showed the strongest response to acetone gas at 200 °C. The underlying mechanism for the enhanced sensing performance of the Fe₂O₃-functionalized In₂O₃ nanowire sensor towards acetone gas is discussed.     

Photoluminescence characteristics of ZnGa2O4 thin films prepared by chemical solution method

Zinc gallate (ZnGa₂O₄) thin film phosphors have been formed on ITO glass substrates by a chemical solution method with starting materials of zinc acetate dihydrate, gallium nitrate hydrate and 2-methoxiethanol as a solution. The thin films were firstly dried at 100 °C and fired at 500 °C for 30 min and then, annealed at 500 °C and 600 °C for 30 min under an annealing atmosphere of 3% H₂/Ar. XRD patterns of the thin film phosphors showed (311) and (220) peak indicating ZnGa₂O₄ crystalline phase in which all the (311) peaks of the film phosphors synthesized on ITO glass and soda-lime glass revealed high intensity with increasing annealing temperature from 500 °C to 600 °C. The ZnGa₂O₄ thin film phosphors represented marked change in AFM surface morphologies according to an annealing temperature under an annealing atmosphere (3% H2/Ar). The film phosphor, annealed at 600 °C, showed the embossed pattern with relatively regular spacing in AFM surface morphology. The ZnGa₂O₄ thin film phosphors formed on ITO glass, which were annealed at different temperatures and showed distinctive spectra with peak wavelengths of 434 nm and 436 nm in the blue emission region.     

Synthesis of SmAlO<Subscript>3</Subscript> nanocrystalline powders by polymeric precursor method

SmAlO₃ nanocrystalline powders were successfully synthesized by the polymeric precursor method using ethylenediaminetetraacetic acid as a chelating agent. The precursor and the derived powders were characterized by thermogravimetry analysis (TG) and differential scanning calorimetry analysis (DSC), infrared spectroscopy (IR), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The results showed that pure SmAlO₃ powder with orthorhombic perovskite structure could be synthesized at 800°C for 2 h without formation of any intermediate phase. The average particle size of the powder synthesized at 900°C was as low as 28 nm. Subsequently, the bulk SmAlO₃ ceramics were prepared at various sintering temperatures using the synthesized powders calcined at 900°C for 2 h as starting materials. The sintering experiments indicated that the sample sintered at 1550°C for 2 h exhibited the highest relative density of 97.2% and possessed the best microwave dielectric properties of ε _r=20.94, Q×f=78600 GHz and τ _f=−71.8 ppm/°C.     

Preferential regrowth of indium–tin oxide (ITO) films deposited on GaN (0001) by rf-magnetron sputter

Effects of thermal treatments on the electrical properties and microstructures of indium–tin oxide (ITO)/GaN contacts have been investigated using a rf-magnetron sputter deposition followed by rapid thermal annealing. ITO films annealed at 800 °C revealed Schottky contact characteristics with a barrier height corresponding to ITO’s work function of 4.62 eV. The evolution of electrical properties of ITO/GaN contacts was attributed to the preferential regrowth of In₂O₃ (222)//GaN (0001) with an ideal metal–semiconductor Schottky contact. The feasible use of ITO/GaN as a transparent Schottky contact would be realized by the enhanced regrowth of In₂O₃ at high temperature. Received: 1 September 2000 / Accepted: 15 November 2000 / Published online: 28 February 2001     

Soft chemistry routes for synthesis of rare earth oxide nanoparticles with well defined morphological and structural characteristics

Phosphors of (Y_0.75Gd_0.25)₂O₃:Eu³⁺ (5 at.%) have been prepared through soft chemistry routes. Conversion of the starting nitrates mixture into oxide is performed through two approaches: (a) hydrothermal treatment (HT) at 200 °C/3 h of an ammonium hydrogen carbonate precipitated mixture and (b) by thermally decomposition of pure nitrate precursor solution at 900 °C in dispersed phase (aerosol) within a tubular flow reactor by spray pyrolysis process (SP). The powders are additionally thermally treated at different temperatures: 600, 1000, and 1100 °C for either 3 or 12 h. HT—derived particles present exclusively one-dimensional morphology (nanorods) up to the temperatures of 600 °C, while the leaf-like particles start to grow afterward. SP—derived particles maintain their spherical shape up to the temperatures of 1100 °C. These submicron sized spheres were actually composed of randomly aggregated nanoparticles. All powders exhibits cubic Ia-3 structure (Y_0.75Gd_0.25)₂O₃:Eu and have improved optical characteristics due to their nanocrystalline nature. The detailed study of the influence of structural and morphological powder characteristics on their emission properties is performed based on the results of X-ray powder diffractometry, scanning electron microscopy, X-ray energy dispersive spectroscopy, transmission electron microscopy, and photoluminescence measurements.     

Conducting properties of In2O3:Sn thin films at low temperatures

Electrical conductivity, Hall effect and magnetoresistance of In₂O₃:Sn thin films deposited on a glass substrates at different temperatures and oxygen pressures, have been investigated in the temperature range 4.2–300 K. The observed temperature dependences of resistivity for films deposited at 230 °C as well as at nominally room temperatures were typical for metallic transport of electrons except temperature dependence of resistivity of the In₂O₃:Sn film deposited in the oxygen deficient atmosphere. The electrical measurements were accompanied by AFM and SEM studies of structural properties, as well as by XPS analysis. It is established that changes of morphology and crystallinity of ITO films modify the low-temperature behavior of resistivity, which still remains typical for metallic transport. This is not the case for the oxygen deficient ITO layer. XPS analysis shows that grown in situ oxygen deficient ITO films have enhanced DOS between the Fermi level and the valence band edge. The extra localized states behave as acceptors leading to a compensation of n-type ITO. That can explain lower n-type conductivity in this material crossing over to a Mott-type hopping at low temperatures. Results for the low temperature measurements of stoichiometric ITO layers indicate that they do not show any trace of metal-to-insulator transition even at 4.2 K. We conclude that, although ITO is considered as a highly doped wide-band gap semiconductor, its low-temperature properties are very different from those of conventional highly doped semiconductors.     

Proton conductivity and low temperature structure of In-doped BaZrO3

The proton conductivity and structural features of In³⁺ substituted BaZrO₃ samples, i.e., BaZr_1−xIn_xO_3−δ, were investigated. Rietveld analysis of low temperature (10 K) neutron powder diffraction data collected on as-prepared and deuterated samples confirmed cubic symmetry (space group Pm-3m) for all compositions. The level of oxygen vacancies refined in the as-prepared samples were in good agreement with the values expected to conserve charge neutrality, whilst an increase in oxygen occupancy, reflecting the incorporation of OD⁻ species, was obtained for the deuterated materials. An expansion of the unit cell parameter, a, was observed as a function of In³⁺ doping as well as after the deuteration reaction. The conductivity of pre-hydrated and dry samples was measured using impedance methods. For 25% In-doped BaZrO₃, the low T (300 °C) conductivity of the heating cycle of the dried sample was greater than that of the cooling cycle of the pre-hydrated sample indicating a greater number of protons in the nominally dry sample. In contrast, the conductivity values were similar at higher temperatures e.g. T > 500 °C where proton conduction is not dominant.     

Search for new transparent conductors: Effect of Ge doping on the conductivity of Ga2O3, In2O3 and Ga1.4In0.6O3

Only a small amount (≤3.5 mol%) of Ge can be doped in Ga₂O₃, Ga_1.4In_0.6O₃ and In₂O₃ by means of solid state reactions at 1400 °C. All these samples are optically transparent in the visible range, but Ge-doped Ga₂O₃ and Ga_1.4In_0.6O₃ are insulating. Only Ge-doped In₂O₃ exhibits a significant decrease in resistivity, the resistivity decreasing further on thermal quenching and H₂ reduction. The resistivity of 2.7% Ge-doped In₂O₃ after H₂ reduction shows a metallic behavior, and a resistivity of ～1 mΩ cm at room temperature, comparable to that of Sn-doped In₂O₃.     

Electron trapping center and SnO2-doping mechanism of indium tin oxide

Indium tin oxide (ITO) and Er³⁺-doped ITO powders were prepared by a conventional ceramic method. The density of ITO powders and optical absorption spectra of Er³⁺ ions in Er³⁺-doped ITO were measured as a function of the SnO₂ doping level. The results obtained were discussed in terms of the trapping center for immobile electrons in ITO. Observed densities of ITO powders were in good agreement with those calculated from their lattice parameters, assuming that the immobile electrons were trapped at the excess interstitial oxygen. The optical absorption spectra of Er³⁺-doped ITO indicated that some In³⁺ ions in ITO were surrounded by 7 and/or 8 oxygen ions; the increase in the coordination number of In³⁺ from 6 in In₂O₃ to 7 and/or 8 in ITO must be caused by the introduction of excess interstitial oxygen into the quasi-anion site in the C-typerare-earth lattice upon SnO₂ doping. It was concluded that the immobile electrons in ITO are trapped at the excess interstitial oxygen, and that the mechanism of conduction carrier generation and compensation upon SnO₂ doping into In₂O₃ can be expressed by the defect equation, 2SnO₂?2Sn_In·+2(1-z)e^′+zO_i ^′′+3O_O ^×+(1-z)/2O₂. Received: 26 November 1999 / Accepted: 20 April 2000 / Published online: 13 September 2000     

Electrical conductivity of fully densified nano CaZr0.90In0.10O3 − δ ceramics prepared by a water-based gel precipitation method

Water-based gel precipitation method was first applied to synthesize high purity nano CaZr_0.90In_0.10O_3 ? δ powders suitable for fabricating dense ceramics at lower temperature. By using CaCO₃, Zr(NO₃)₄ and In(NO₃)₃ as raw materials, PEG as dispersant, CaZr_0.90In_0.10O_3 ? δ with an average particle size of about 40 nm was obtained at 850 °C, which was nearly 350 °C lower than that of traditional solid-state reaction method. Fully densified ceramics with an average grain size of 200–300 nm were obtained at 1350 °C, a temperature about 250 °C lower than that of traditional sintering techniques. Experimental results showed that the flexure stress, total, bulk and grain boundary protonic conductivities of the ceramics were more favorable than those of the ceramics fabricated at 1500 °C and 1600 °C from the powders synthesized by solid-state reaction method.     

Fabrication and characterization of CdS-sensitized TiO<Subscript>2</Subscript> nanotube photoelectrode

CdS quantum dot (Qd)-sensitized TiO₂ nanotube array photoelectrode is synthesised via a two-step method on tin-doped In₂O₃-coated (ITO) glass substrate. TiO₂ nanotube arrays are prepared in the ethylene glycol electrolyte solution by anodizing titanium films which are deposited on ITO glass substrate by radio frequency sputtering. Then, the CdS Qds are deposited on the nanotubes by successive ionic layer adsorption and reaction technique. The resulting nanotube arrays are characterized by scanning electron microscopy, X-ray diffraction (XRD) and UV–visible absorption spectroscopy. The length of the obtained nanotubes reaches 1.60 μm and their inner diameter and wall thickness are around 90 and 20 nm, respectively. The XRD results show that the as-prepared TiO₂ nanotubes array is amorphous, which are converted to anatase TiO₂ after annealed at 450 °C for 2 h. The CdS Qds deposited on the TiO₂ nanotubes shift the absorption edge of TiO₂ from 388 to 494 nm. The results show that the CdS-sensitized TiO₂ nanotubes array film can be used as the photoelectrode for solar cells.     

Synthesis of indium oxide nanoparticles by solid state chemical reaction

A three stage process consisting of mechanical milling, heat treatment, and washing has been investigated as a means of manufacturing nanoparticulate powders of In₂O₃. In the first stage of processing, mechanical milling was used to prepare a nanocrystalline mixture of In₂(SO₄)₃, Na₂CO₃, and NaCl. Subsequent heat treatment of the milled reactant resulted in the formation of nanocrystalline In₂O₃ particles embedded within a matrix of Na₂SO₄ and NaCl. In the final stage of processing, the In₂O₃ powder was recovered by washing with deionised water. The duration of milling was found to determine the degree of hard agglomeration in the final washed powder. It was also found that the average particle size of the powder could be controlled between 8 and 18 nm by simply varying the temperature of the post-milling heat treatment over the range of 400 to 550°C. These results demonstrate that solid state chemical reaction can be used as a technically simple method for manufacturing nanoparticulate In₂O₃ powders with a controlled particle size and low levels of hard agglomeration.     

Studies on chemical stability in CO2 and H2O and electrical conductivity of perovskite-type Ba3In2Zr1?xCexO8 (x?= 0, 0.5, 1)

We report the synthesis, structure, microstructure, chemical stability in H₂O and CO₂, and electrical transport properties of an oxide ion-conducting perovskite-related structure Ba₃In₂MO₈ (M = Zr, Ce, Zr_0.5Ce_0.5). Powder X-ray diffraction confirmed the formation of a simple cubic perovskite-like structure for Ba₃In₂ZrO₈ (a = 4.205(9) ?), Ba₃In₂CeO₈ (a = 4.234(1) ?), and Ba₃In₂Zr_0.5Ce_0.5O₈ (a = 4.285(8) ?). The increase in lattice constant is consistent with the Shannon’s ionic radius trend. Among the three samples investigated, Ba₃In₂ZrO₈ was found to be stable against reaction with pure CO₂ at elevated temperature, while the Ce and 1:1 Zr and Ce compounds were unstable at 600 °C. Ba₃In₂ZrO₈, Ba₃In₂CeO₈, and Ba₃In₂Zr_0.5Ce_0.5O₈ were found to be chemically unstable in H₂O at about 50 °C. The bulk electrical conductivity of the samples prepared at different temperatures was found to be nearly the same; the total conductivity (bulk + grain–boundary + electrode) seems to change with sintering temperature. Both Ba₃In₂ZrO₈ and Ba₃In₂CeO₈, prepared at 1,400 °C, exhibited comparable electrical conductivity of about 6 × 10⁻³ S cm⁻¹ at 800 °C, which is comparable to that of conventional Y₂O₃-doped ZrO₂ electrolyte. These compounds are very promising electroltes, provided that their chemical and mechnical stabitities are improved without losing any ionic conductivity.     

Morphological,photovoltaic, and electron transport properties of In2O3-based DSSC with different concentrations of MWCNTs

This study focuses on the influence of loading MWCNTs in In₂O₃-based DSSCs. In₂O₃-MWCNTs were prepared by sol-gel method via spin coating technique and annealed at 450 °C. The structural, morphology, and electrical properties of the photoanodes were characterized by means of XRD, AFM and FESEM, and J-V curve measurement and EIS properties, respectively. Incorporation of MWCNTs in In₂O₃ improved the J _sc and V _oc of the cell. However, excess loading of MWCNTs in In₂O₃ caused a serious aggregation of MWCNTs that increased the recombination rate. Thus, In₂O₃-MWCNTs with 0.3 % of MWCNTs achieved the highest PCE of 1.23 % with large surface area for efficient dye adsorption. Moreover, In₂O₃-MWCNTs_(0.3%) exhibited large D _eff about 25.7 × 10⁻³ cm² s⁻¹ with low recombination effect that increased the PCE. This study suggests an optimum MWCNT incorporation of 0.3 % in the photoanode by sol-gel synthesis method of developing In₂O₃-based nanocomposite.

     

Structure and NO2 gas sensing properties of SnO2-core/In2O3-shell nanobelts

SnO₂-core/In₂O₃-shell nanobelts were fabricated by a two-step process comprising thermal evaporation of Sn powders and sputter-deposition of In₂O₃. Transmission electron microscopy and X-ray diffraction analyses revealed that the core of a typical core–shell nanobelt comprised a simple tetragonal-structured single crystal SnO₂ and that the shell comprised an amorphous In₂O₃. Multiple networked SnO₂-core/In₂O₃-shell nanobelt sensors showed the response of 5.35% at a NO₂ concentration of 10 ppm at 300 °C. This response value is more than three times larger than that of bare-SnO₂ nanobelt sensors at the same NO₂ concentration. The enhancement in the sensitivity of SnO₂ nanobelts to NO₂ gas by sheathing the nanobelts with In₂O₃ can be accounted for by the modulation of electron transport by the In₂O₃–In₂O₃ homojunction.     

Preparation of Y2O3:Eu thin films by excimer-laser-assisted metal organic deposition

Europium-doped yttrium oxide (Y₂O₃:Eu) thin films were successfully deposited on quartz and ITO/glass substrates by excimer-laser-assisted metal organic deposition (ELAMOD) at low temperatures. The effects of laser wavelength and thermal temperature on the films’ crystallinity and photoluminescence properties were investigated. Films irradiated by an ArF laser at 80 mJ/cm² and 400–500°C were highly crystallized compared with those prepared by thermal MOD. In contrast, when the film was irradiated by a KrF laser at 500°C, no crystalline Y₂O₃:Eu was formed. The Y₂O₃:Eu film irradiated by the ArF laser at 80 mJ/cm² and 500°C showed typical PL spectra of Eu³⁺ ions with cubic symmetry and a ⁵D₀→⁷F₂ transition at ∼612 nm. The PL intensity at 612 nm was much higher for the film prepared with ELAMOD than for that prepared by the thermal-assisted process, and the photoemission intensity of the film prepared with ELAMOD strongly depended on the substrate material.     

Synthesis and structural characterization of perovskite type proton conducting BaZr1−xInxO3−δ (0.0 ≤ x ≤ 0.75)

Solid state sintering has been used to prepare the cubic perovskite structured compounds BaZr_1−xIn_xO_3−δ (0.0 ≤ x ≤ 0.75). Analysis of X-ray powder diffraction (XRPD) data reveals that the unit cell parameter, a, increases linearly with an increased Indium concentration. XRPD data was also used to demonstrate the completion of sample hydration, which was reached when the materials showed a set of single-phase Bragg-peaks. Dynamic thermogravimetric analysis (TGA) data showed that approx. 89% of the total number of available oxygen vacancies can be filled in BaZr_1−xIn_xO_3−δ for x = 0.50, and that the maximum water uptake occurs below 300 °C. Rietveld analysis of the room temperature neutron powder diffraction (NPD) data confirmed the average cubic symmetry (space group Pm-3m), and an expansion of the unit cell parameter after the hydration reaction. The strong O–H stretch band, 2500–3500 cm^− 1, in the infrared absorbance spectrum clearly manifests the presence of protons in the hydrated material. Proton conductivity of hydrated BaZr_1−xIn_xO_3−δ, x = 0.75 was investigated during heating and cooling cycles under dry argon atmosphere. The total conductivity during the heating cycle was nearly two orders of magnitude greater than that of cooling cycle at 300 °C, whilst these values were similar at higher temperatures i.e. T > 600 °C.     

Crystallization and conductivity of 2CaO–La2O3–5P2O5 glass–ceramic with Al2O3 addition

Al₂O₃ was added to a 2CaO–La₂O₃–5P₂O₅ metaphosphate, to replace 10% of the Ca²⁺ ions by Al³⁺, forming a phosphate with the nominal composition 1.8CaO–0.1Al₂O₃–La₂O₃–5P₂O₅. The effect of Al₂O₃ addition and heat treatment on the microstructure and conductivity of the resulting glass–ceramics was investigated by XRD, SEM, TEM, and AC impedance spectroscopy. Upon transformation from glass to glass–ceramic, conductivities increased significantly. The glasses were isochronally transformed at 700 and at 800 °C for 1 h or 5 h, in air, following heating at 3 or 10 °C/min. With Al₂O₃ addition, after a heat treatment at 700 °C, 100–300 nm nano-domains of LaP₃O₉ crystallized from the glass matrix. Annealing at 800 °C produced a further order of magnitude conductivity increase for the Al-free glass, but less so for the Al-containing glass.     

Synthesis and characterization of nanocrystalline MgAl2O4 spinel by polymerized complex method

Ultrafine MgAl₂O₄ powder has been synthesized by a polymerized complex method. Heating of a precursor solution containing citric acid (CA), ethylene glycol (EG) and Mg and Al salts with a molar ratio of Mg/Al/CA/EG=1/2/8/32 at 180°C produced a transparent polymeric gel, which have been characterized by FT-IR spectroscopy and TG/DTA. The organic fraction was removed by controlled thermal treatments (350–1200°C) whereby the bimetallic oxide was formed. XRD analysis showed the presence of MgAl₂O₄ at 600°C. TEM observation showed that the spherical nanosized powders with good uniformity was obtained. Furthermore, these powders showed excellent sinterability, relative density up to 99.8% was achieved when sintered at 1550°C for 3 h in air without any sintering additive.