Electrochromic modulation of near-infrared light by WO<Subscript>3</Subscript> films deposited on silver nanowire substrates

Silver nanowire (Ag NW) transparent conductive electrodes with high conductivity and optical transmittance are fabricated. Then, WO₃ films are deposited on Ag NW electrodes by an electrochemical deposition method. The WO₃/Ag NW films act as obvious optical modulators in the visible region. More importantly, the WO₃/Ag NW films have distinct advantage on NIR modulation over conventional WO₃/ITO electrode. Meanwhile, the WO₃/Ag NW films own high electrochromic efficiency of 86.9 cm² C^?1 at NIR region of 1100 nm. Furthermore, electrochromic devices (ECDs) based on Ag NW substrates are fabricated in this study, which exhibit excellent cycling stability and distinct modulation of near-infrared light compared with ITO-based ECDs. This work is the first study that reports the application of Ag NW-based electrochromic films and electrochromic devices in modulation of NIR light. It exhibits bright prospects that the electrochromic materials deposited on Ag NW electrodes may find potential application in thermal control and emission detectors for spacecraft.     

Rutile TiO<Subscript>2</Subscript> films as electron transport layer in inverted organic solar cell

Titanium dioxide (TiO₂) thin films were prepared by sol–gel spin coating method and deposited on ITO-coated glass substrates. The effects of different heat treatment annealing temperatures on the phase composition of TiO₂ films and its effect on the optical band gap, morphological, structural as well as using these layers in P3HT:PCBM-based organic solar cell were examined. The results show the presence of rutile phases in the TiO₂ films which were heat-treated for 2 h at different temperatures (200, 300, 400, 500 and 600 °C). The optical properties of the TiO₂ films have altered by temperature with a slight decrease in the transmittance intensity in the visible region with increasing the temperature. The optical band gap values were found to be in the range of 3.28–3.59 eV for the forbidden direct electronic transition and 3.40–3.79 eV for the allowed direct transition. TiO₂ layers were used as electron transport layer in inverted organic solar cells and resulted in a power conversion efficiency of 1.59% with short circuit current density of 6.64 mA cm^?2 for TiO₂ layer heat-treated at 600 °C.     

Optimization of the thickness of glass/TiO2/Ag/Ti/TiO2/SiON multilayer film

The TiO₂/Ag/Ti/TiO₂/SiON multilayer film was deposited on glass substrate at room temperature using magnetron sputtering method. By varying the thickness of each layer, the optical property was optimized to achieve good selective spectral filtering performance in Vis-NIR region. The multilayer film achieves maximum transmittance of 92.7% at 690 nm, in which the both TiO₂ layers are 33 nm. For good conductivity and transmittance, a 4 nm Ti layer and a 30 nm SiON layer are necessary.     

Plasmonic Oxygen-Deficient TiO2-x Nanocrystals for Dual-Band Electrochromic Smart Windows with Efficient Energy Recycling

Dual-band electrochromic smart windows capable of the spectrally selective modulation of visible (VIS) light and near-infrared (NIR) can regulate solar light and solar heat transmittance to reduce the building energy consumption. The development of these windows is however limited by the number of available dual-band electrochromic materials. Here, plasmonic oxygen-deficient TiO_2-x nanocrystals (NCs) are discovered to be an effective single-component dual-band electrochromic material, and that oxygen-vacancy creation is more effective than aliovalent substitutional doping to introduce dual-band properties to TiO₂ NCs. Oxygen vacancies not only confer good near-infrared (NIR)-selective modulation, but also improve the Li⁺ diffusion in the TiO_2-x host, circumventing the disadvantage of aliovalent substitutional doping with ion diffusion. Consequently optimized TiO_2-x NC films are able to modulate the NIR and visible light transmittance independently and effectively in three distinct modes with high optical modulation (95.5% at 633 nm and 90.5% at 1200 nm), fast switching speed, high bistability, and long cycle life. An impressive dual-band electrochromic performance is also demonstrated in prototype devices. The use of TiO_2-x NCs enables the assembled windows to recycle a large fraction of energy consumed in the coloration process (“energy recycling”) to reduce the energy consumption in a round-trip electrochromic operation.     

Transparent conductive and infrared reflective AZO/Cu/AZO multilayer film prepared by RF magnetron sputtering

AZO/Cu/AZO multilayer films were prepared on glass substrate by radio frequency magnetron sputtering technology. The prepared films were investigated by a four-point probe system, X-ray diffraction, optical transmittance spectra, scanning electron microscope, atomic force microscopy and Fourier transform infrared spectroscopy. The results showed that Cu inner layer started forming a continuous film at the thickness around 11 nm. The prepared AZO/Cu/AZO samples exhibited the visible transmittance of 60–80 % and sample with 15 nm Cu inner layer showed the highest infrared reflection rate of 67 % in FIR region and the lowest sheet resistance of 16.6 Ω/sq. The proper visible transmittance and infrared reflection property of the AZO/Cu/AZO multilayer film make it a promising candidate for future energy conservation materials.     

Effect of substrate temperature on structural, morphological and optical properties of crystalline titanium dioxide films prepared by DC reactive magnetron sputtering

Titanium dioxide (TiO₂) thin films have been deposited with various substrate temperatures by dc reactive magnetron sputtering method onto glass substrate. The effects of substrate temperature on the crystallization behavior and optical properties of the films have been studied. Chemical composition of the films was investigated by X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) analysis of the films revealed that they have polycrystalline tetragonal structure with strong (101) texture. The surface morphological study revealed the crystalline nature of the films at higher substrate temperatures. The TiO₂ films show the main bands in the range 400–700 cm^?1, which are attributed to Ti–O stretching and Ti–O–Ti bridging. The transmittance spectra of the TiO₂ thin film measured with various substrate temperatures ranged from 75 to 90 % in the visible light region. The optical band gap values of the films are increasing from 3.44 to 4.0 eV at growth temperature from 100 to 400 °C. The structural and optical properties of the films improved with the increase in the deposition temperature.     

Influence of Ag thickness on electrical, optical and structural properties of nanocrystalline MoO3/Ag/ITO multilayer for optoelectronic applications

In this study, MoO₃/Ag/ITO/glass (MAI) nano-multilayer films were deposited by the thermal evaporation technique and then were annealed in air atmosphere at 200 °C for 1 h. The effects of Ag layer thickness on electrical, optical and structural properties of the MoO₃(45 nm)/Ag(5-20 nm)/ITO(45 nm)/glass nano-multilayer films were investigated. The sheet resistance decreased rapidly with increasing Ag thickness. Above a thickness of 10 nm, the sheet resistances became somewhat saturated to a value of 3(Ω/□). The highest transparency over the visible wavelength region of spectrum (85%) was obtained for 10 nm Ag layer thickness. Carrier mobility, carrier concentrations, transmittance and reflectance of the layers were measured. The allowed direct band-gap for an Ag thickness range 5-20 nm was estimated to be in the range 3.58-3.71 eV. The XRD pattern showed that the films were polycrystalline. X-ray diffraction has shown that Ag layer has a (111) predominant orientation when deposited. The figure of merit was calculated for MAI multilayer films. It has been found that the Ag layer thickness is a very important factor in controlling the electrical and optical properties of MAI multilayer films. The optimum thickness of the Ag layer for these films was determined. The results exhibit that the MAI transparent electrode is a good structure for use as the anode of optoelectronic devices.     

Fabrication of TiO2 thin film memristor device using electrohydrodynamic inkjet printing

In this paper, we are reporting the fabrication of memristor device (Ag/TiO₂/Cu) using electrohydrodynamic inkjet printing technology. The titanium oxide (TiO₂) active layer was deposited using electrohydrodynamic atomization technique. The metal electrodes were patterned by using electrohydrodynamic printing technique. The crystalline nature, surface morphology and optical properties of as deposited TiO₂ films were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM) and UV-visible spectroscopic analysis respectively. XRD and SEM studies revealed that the presence of anatase TiO₂ with uniform deposition. The optical transmittance of the deposited TiO₂ films was observed to be 87% in the visible region. The fabricated memristor device (Ag/TiO₂/Cu) exhibits bipolar resistive switching behavior within the low operating voltage (± 0.7 V). Our results ensure that the printed technology provides breakthrough solution in the electronic memory device fabrication.     

Dependence of structural, optical and electrical properties on substrate temperature for hexagonal MgxZn1−xO films

Single hexagonal-phase Mg_xZn_1?xO films were deposited on glass substrates by pulsed laser deposition from a ZnO target mixed with MgO. The effect of substrate temperature on the structural, electrical and optical properties was investigated by X-ray diffraction and the transmittance measurements. It was observed that Mg incorporation lead to a clear shift of the (002) peak position to lower angle with reference to pure ZnO films due to the residual stress change with deposition temperature. It was also found that Mg doping increased the resistivity by 2 orders of magnitude and the maximum resistivity was 0.072 Ω·cm at 550 °C with the carrier concentration of 1.1 × 10¹⁹ cm^?3. The visible transmittance of above 80 % was obtain in the alloy films, which optical band gap was observed to increase with the substrate temperature, attaining 3.85 eV at 600 °C. The possible mechanism was discussed.     

Structural, electrical and optical properties of ITO films with a thin TiO2 seed layer prepared by RF magnetron sputtering

Tin-doped indium oxide (ITO) films were deposited by RF magnetron sputtering on TiO₂-coated glass substrates (the TiO₂ layer is usually called seed layer). The properties of ITO films prepared at a substrate temperature of 300 °C on bare and TiO₂-coated glass substrates have been analyzed by using X-ray diffraction, atomic force microscope, optical and electrical measurements. Comparing with single layer ITO film, the ITO film with a TiO₂ seed layer of 2 nm has a remarkable 41.2% decrease in resistivity and similar optical transmittance. The glass/TiO₂ (2 nm)/ITO film achieved shows a resistivity of 3.37 × 10⁻⁴ Ω cm and an average transmittance of 93.1% in the visible range. The glass/TiO₂ may be a better substrate compared with bare glass for depositing high quality ITO films.     

Study of optoelectronics and microstructures on the AZO/nano-layer metals/AZO sandwich structures

In this study, growth nano-layer metals (Al, Cu, Ag) and Al-doped ZnO (AZO) thin films are deposited on glass substrates as the transparent conducting oxides (TCOs) to form AZO/nano-layer metals/AZO sandwich structures. The conductivity properties of thin films are enhanced when the average transmittance over the wavelengths 400–800 nm is maintained at higher than 80 %. A radio frequency magnetron sputtering system is used to deposit the metal layers and AZO thin films of different thickness, to form AZO/Al/AZO (ALA), AZO/Cu/AZO (ACA) and AZO/Ag/AZO (AGA) structures. X-ray diffraction and field emission scanning electron microscopy are used to analyze the crystal orientation and structural characteristic. The optical transmission and resistivity are measured by UV–VIS–NIR spectroscopy and Hall effect measurement system, respectively. The results show that when the Ag thickness is maintained at approximately 9 nm, the TCOs thin film has the lowest resistivity of 8.9 × 10^?5 Ω-cm and the highest average transmittance of 81 % over the wavelengths 400–800 nm. The crystalline Ag nano-crystal structures are observed by high-resolution transmission electron microscopy. In addition, the best figure of merit for the AZO/Ag/AZO tri-layer film is 2.7 × 10^?2 (Ω^?1), which is much larger than that for other structures.     

Effects of intermediate metal layer on the properties of Ga–Al doped ZnO/metal/Ga–Al doped ZnO multilayers deposited on polymer substrate

Ga–Al doped ZnO/metal/Ga–Al doped ZnO multilayer films were deposited on polyethersulfone (PES) substrate at room temperature. The multilayer films consisted of intermediate Ag metal layers, top and bottom Ga–Al doped ZnO layer. The multilayer with PES substrate had advantages such as low sheet resistance, high optical transmittance in visible range and stable mechanical properties. From the results, sheet resistances of multilayer showed 9 Ω/sq with 12 nm of Ag metal layer thickness. Average optical transmittance of multilayer film showed 84% in visible range (380–770 nm) with 12 nm of Ag metal layer thickness. Moreover the multilayers showed stable mechanical properties than single-layered Ga–Al doped ZnO sample during the bending test due to the existence of ductile Ag metal layer.     

Fabrication of a novel SnO2:Al/ZnO:F bi-layer for opto-electronic applications

Single layered aluminium doped tin oxide (ATO), fluorine doped zinc oxide (FZO) and bi-layered ATO/FZO thin films were deposited onto preheated glass substrates (T_s = 340 ± 5 °C) using a low-cost and simplified spray pyrolysis technique. The structural, optical, electrical and surface morphological properties of the bi-layered ATO/FZO thin films were studied and compared with that of the single layered films. The average optical transmittance of the bi-layer film in the visible range was found to be around 80 %. The bi-layered ATO/FZO films possessed both better transmittance in the visible range and sharp absorption edge, the unique desirable features of ATO and FZO films, respectively. The optical band gap (E_g) value of the bi-layer coating (3.22 eV) was found to lie between the E_g values of single layered ATO (3.71 eV) and FZO (3.20 eV) films. Sheet resistance values of ATO and FZO single layer films were 3.47 and 11.2 kΩ/sq., respectively. The bi-layered ATO/FZO thin films exhibited a sheet resistance of 4.42 kΩ/sq. which was very much close to that of ATO films and three times less than that of FZO film. The AFM images showed the good packing density and homogeneity of the surface of the bi-layer films. The annealing studies clearly showed that the ATO over layer remarkably improved the thermal stability of the bi-layered film.     

Synthesis of core/shell Ti/TiOx photocatalyst via single-mode magnetic microwave assisted direct oxidation of TiH2

Submicron core/shell Ti/TiO_x photocatalyst is successfully synthesized via single-mode magnetic microwave (SMMW) assisted direct oxidation of planetary ball-milled TiH₂. The thickness of TiOx shell including highly concentrated defects such as Ti³⁺ and/or oxygen vacancies is controllable in the range from 6 to over 18 nm by varying the treatment time in the SMMW assisted reaction. In addition to its quite narrow optical bandgap (1.34–2.69 eV) and efficient visible-light absorption capacity, the submicron Ti/TiO_x particle exhibits superior photocatalytic performance towards H₂ production from water under both UV and visible-light irradiation to compare with a commercial TiO₂ photocatalyst (P-25). Such excellent performance can be achieved by the synergetic effect of enhancement in visible light absorption capacity and photo-excited carrier separation because of the highly concentrated surface defects and the specific Ti/TiO_x core/shell structure, respectively.     

Quality enhancement of AZO thin films at various thicknesses by introducing ITO buffer layer

Due to the simultaneously superior optical transmittance and low electrical resistivity, transparent conductive electrodes play a significant role in semiconductor electronics. To enhance the electrical properties of these films, one approach is thickness increment which degrades the optical properties. However, a preferred way to optimize both electrical and optical properties of these layers is to introduce a buffer layer. In this work, the effects of buffer layer and film thickness on the structural, electrical, optical and morphological properties of AZO thin films are investigated. Al-doped zinc oxide (AZO) is prepared at various thicknesses of 100 to 300 nm on the bare and 100 nm-thick indium tin oxide (ITO) coated glass substrates by radio frequency sputtering. Results demonstrate that by introducing ITO as a buffer layer, the average values of sheet resistance and strain within the film are decreased (about 76 and 3.3 times lower than films deposited on bare glasses), respectively. Furthermore, the average transmittance of ITO/AZO bilayer is improved nearly 10% regarding single AZO thin film. This indicates that bilayer thin films show better physical properties rather than conventional monolayer thin films. As the AZO film thickness increases, the interplanar spacing, d₍₀₀₂₎, strain within the film and compressive stress of the film in the hexagonal lattice, decreases indicating the higher yield of AZO crystal. Moreover, with the growth in film thickness, carrier concentration and optical band gap (E_g) of AZO film are increased from 4.62?×?10¹⁹ to 8.21?×?10¹⁹ cm^?3 and from 3.55 to 3.62 eV, respectively due to the Burstein-Moss (BM) effect. The refractive index of AZO thin film is obtained in the range of 2.24–2.26. With the presence of ITO buffer layer, the AZO thin film exhibits a resistivity as low as 6?×?10^?4 Ω cm, a sheet resistance of 15 Ω/sq and a high figure of merit (FOM) of 1.19?×?10⁴ (Ω cm)^?1 at a film thickness of 300 nm. As a result, the quality of AZO thin films deposited on ITO buffer layer is found to be superior regarding those grown on a bare glass substrate. This study has been performed over these two substrates because of their significant usage in the organic light emitting diodes and photovoltaic applications as an enhanced carrier injecting electrodes.     

Absorbing TiOx thin film enabling laser welding of polyurethane membranes and polyamide fibers

We report on the optical properties of thin titanium suboxide (TiO_x) films for applications in laser transmission welding of polymers. Non-absorbing fibers were coated with TiO_x coatings by reactive magnetron sputtering. Plasma process parameters influencing the chemical composition and morphology of the deposited thin films were investigated in order to optimize their absorption properties. Optical absorption spectroscopy showed that the oxygen content of the TiO_x coatings is the main parameter influencing the optical absorbance. Overtreatment (high power plasma input) of the fiber surface leads to high surface roughness and loss of mechanical stability of the fiber. The study shows that thin substoichiometric TiO_x films enable the welding of very thin polyurethane membranes and polyamide fibers with improved adhesion properties.     

Determination of the optical constants of As–Se–Ag chalcogenide thick films with high precision for optoelectronics applications

Thin films of (As₅₀Se₅₀)_100?xAg_x (with 0?≤?x?≤?25 s) metal-chalcogenide glasses were deposited onto glass substrates by thermal evaporation technique under high vacuum (10^?6 mbar). The optical constants as well as the average thickness of the studied films are determined by the Swanepoel envelope method which is based on the optical transmission spectra measured in the spectral range 300–2500 nm. This method enables the transformation of the optical-transmission spectrum of a thin film of wedge-shaped thickness into the spectrum of a uniform film, whose thickness is equal to the average thickness of the non-uniform layer. The dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single-oscillator model. The optical absorption edge is described using the non-direct transition model proposed by Tauc relation. Analysis of the optical data revealed that an addition of Ag in the range from 0 to 25 at.% to the (As₅₀Se₅₀)_100?x binary alloys affected the optical parameters of the investigated thin films. For instance, the optical band gap decreased from 1.661 to 1.441 eV with increasing the Ag content from 0 to 25 at.%. The results were discussed in terms of Mott and Davis model as well as chemical-bond approach.     

Organic photovoltaic cells fabricated on a SnOx/Ag/SnOx multilayer transparent conducting electrode

Transparent conducting multilayer structured electrode of a few nm Ag layer embedded in tin oxide thin film SnO_x/Ag/SnO_x was fabricated on a glass by RF magnetron sputtering at room temperature. The multilayer of the SnO_x(40 nm)/Ag(11 nm)/SnO_x(40 nm) electrode shows the maximum optical transmittance of 87.3% at 550 nm and a quite low electrical resistivity of 6.5 × 10^− 5 Ω cm, and the corresponding figure of merit (T¹⁰/R_S) is equivalent to 3.6 × 10^− 2 Ω^− 1. A normal organic photovoltaic (OPV) structure of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/polythiophene:phenyl-C60-butyric acid methyl ester/Al was fabricated on glass/SnO_x/Ag/SnO_x to examine the compatibility of OPV as a transparent conducting electrode. Measured characteristic values of open circuit voltage of 0.62 V, saturation current of 8.11 mA/cm² and fill factor of 0.54 are analogous to 0.63 V, 8.37 mA/cm² and 0.58 of OPV on commercial glass/indium tin oxide (ITO) respectively. A resultant power conversion efficiency of 2.7% is also very comparable with the 3.09% of the same OPV structure on the commercial ITO glass as a reference, and which reveals that SnO_x/Ag/SnO_x can be appropriate to OPV solar cells as a sound transparent conducting electrode.     

Features of and IN SITU measurements on absorbing TiOx films produced by reactive d.c. magnetron-plasmatron sputtering

The use of a d.c. magnetron-plasmatron discharge allows the direct production of TiO_x films with an O:Ti atomic ratio x of 0–2 by variation of the O₂ partial pressure of an ArO₂ gas mixture in the range p_O2/p_tot = 0–0.23. The optical and structural properties of these films are discussed. It is shown that, apart from a typically high condensation rate, this method ensures the necessary reproducibility of the refractive index of TiO₂ films for dielectric multilayer stacks and gives absorbing TiO_x films with defined stoichiometries that are consistent with the requirements for, say, simple solar absorber systems.     

Characterization of ITO/CdO/glass thin films evaporated by electron beam technique

Abstract

A thin buffer layer of cadmium oxide (CdO) was used to enhance the optical and electrical properties of indium tin oxide (ITO) films prepared by an electron-beam evaporation technique. The effects of the thickness and heat treatment of the CdO layer on the structural, optical and electrical properties of ITO films were carried out. It was found that the CdO layer with a thickness of 25 nm results in an optimum transmittance of 70% in the visible region and an optimum resistivity of 5.1×10^?3 Ω cm at room temperature. The effect of heat treatment on the CdO buffer layer with a thickness of 25 nm was considered to improve the optoelectronic properties of the formed ITO films. With increasing annealing temperature, the crystallinity of ITO films seemed to improve, enhancing some physical properties, such as film transmittance and conductivity. ITO films deposited onto a CdO buffer layer heated at 450 °C showed a maximum transmittance of 91% in the visible and near-infrared regions of the spectrum associated with the highest optical energy gap of 3.61 eV and electrical resistivity of 4.45×10^?4 Ω cm at room temperature. Other optical parameters, such as refractive index, extinction coefficient, dielectric constant, dispersion energy, single effective oscillator energy, packing density and free carrier concentration, were also studied.