Transmittance In Visible Region Research Articles

Preparation and electrical characteristics of transparent thin film transistors with sputtered aluminum and phosphorus co-doped indium-zinc-oxide channel layer

Thin film transistors (TFTs) with aluminum and phosphorus co-doped indium-zinc-oxide (IZO:Al,P) channel layer were fabricated by the radio frequency (RF) magnetron sputtering. The IZO:Al,P films were amorphous and highly transparent with exceed 80% transmittance in visible region. High performance IZO:Al,P TFTs have been observed due to the incorporation of Al and P, which serve as an inhibitor against oxygen vacancies and carrier. The electrical properties of IZO:Al,P TFTs were investigated as function of annealing temperatures. The IZO:Al,P TFTs have achieved superior performance (threshold voltage (VTH) of 0.8 V, on-state current (ION) of 1.6 × 10-3 A, off-state current (IOFF) of 2.2 × 10-12 A, µSAT of 39.2 cm2/V∙s and subthreshold swing (S.S.) of 0.68 V/dec.) under the annealing temperature as low as 300 °C.

Synthesis of Al Thin Films with High Optical Transmittance by DC Magnetron Sputtering Process Parameter Optimization

Nanostructured Al thin film with higher optical transmittance and electrical conductivity has intensive applications in solar cells and optical and microelectronic devices. This experimental-based research study has optimized the DC magnetron sputtering deposition parameters (sputtering power, sputtering current, voltage, and working gas pressure) for Al thin film deposition to obtain the highest optical transmittance and lower sheet resistance. Optical transmittance, surface roughness, film thickness, sheet resistance, grain size, and surface morphology were characterized using UV-vis-NIR spectroscopy, surface profiler, spectroscopic ellipsometry, four-point probe, and FE-SEM, respectively to determine the effects of sputtering process parameters on Al films’ different properties. Experimental investigations reveal that electrical conductivity, surface roughness, grain size, and deposition rate increase with increasing of sputtering power at certain working gas pressure. At the optimized condition (sputtering power 80 W, working gas pressure 5 mTorr, deposition time 5 min and ambient temperature), the relatively higher optical transmittance in visible region 96%, moderate sheet resistance 0.196 ohm/square and lowest average surface roughness 2.86 nm were obtained for Al thin film. After all, this research study will help to understand the best Al film deposition parameters in terms of optical transmittance and electrical conductivity for future research and industrial applications.

2D NiOx inverse opal monolayer: Fabrication and improved electrochromic property

Two dimensional (2D) non-stoichiometric NiOx inverse opal (IO) monolayer film was synthesized by ‘dynamic hard template’ infiltration strategy. The novel NiOx 2D IO film shows highly ordered porous array and high transmittance in visible region (>60%). The color change by introducing photonic crystal structure of the IO successfully modifies the color of NiOx film into a pleasant blue-green color. Ni vacancies in NiOx inverse opal monolayer film plays an important role on the electrochromic properties. Due to the introduction of highly ordered inverse opal structure, the obtained NiOx 2D IO film shows an extraordinarily high optical modulation from visible to near-infrared region. The wavelength of the maximum optical density (ΔOD, 0.42) in NiOx inverse opal monolayer film is red-shifted to 480 nm, which coincides with its photonic band gap, in contrast to its plain NiOx film (ΔODmax = 0.33, at 430 nm).

Physical properties of suspension ZnO nanoparticles prepared by wet chemical method: Comparison study

In this work a suspension of Nano-crystalline of ZnO particle is prepared by wet chemical at different temperature and concentration. From FTIR spectral exhibit present of Zn–O bond which indicate to formation ZnO particles. While all suspension and nano films exhibit a high transmittance in visible region about 90% which falls sharply in the UV region. The particle size is measured by using effective mass approximation (EMA), which was approximation (1.7–1.96 nm), and the band gap changes from 3.95 to 4.52eV for nanoparticles in suspension, and change from 3.76 to 3.94 eV for nanoparticles in ZnO film, which is change as function of concentration, temperature and aging time. Hall Effect measurements for ZnO films exhibit n-type conductivity for films deposited with activation energy 0.742eV at high temperature and 0.178eV at low temperature which is different as prepared sample conditions. Also the nanoparticle suspension and nanoparticle film could be implemented as a filter with variable cut off (8.9 × 1014–1.28 × 1015) HZ.

Preparation and Properties of Polyimide Composite Membrane with High Transmittance and Surface Hydrophobicity for Lightweight Optical System.

Polyimide membranes have excellent physiochemical properties which make them valuable materials for optical area. However, common aromatic polyimide membrane trend to show low transmittance in visible region because of the charge-transfer complex (CTC) in molecular structures. Moreover, it’s trending to show high moisture uptakes because of the hydrophilic imide rings in molecular structure. In this work, a polyimide composite membrane with SiO2 antireflective membrane on both sides was prepared. High transmittance (93% within 500~800 nm) and surface hydrophobicity was realized simultaneously. The polyimide composite membrane showed great optical homogeneity. The SiO2 antireflective membranes on polyimide substrate were prepared through a simple and efficient sol-gel method. The surface roughness of polyimide membrane substrate on each side has been improved to 1.56 nm and 3.14 nm, respectively. Moreover, the excellent thermal stability and mechanical property of polyimide membrane has been preserved, which greatly improves the range of applications for the composite membrane. It is a good candidate for light weight optical system.

Regulating the Ni3+/Ni2+ ratio of NiOx by plasma treatment for fully vacuum-deposited perovskite solar cells

Inorganic p-type NiOx was considered as an idea hole-transport layer (HTL) for perovskite solar cells due to its good transmittance in visible region and outstanding chemical stability. The p-type behavior of NiOx is mainly derived from its nonstoichiometric nature and determined by the Ni cation deficiency. Thus, the synthesizing methods play an important role to the electronic properties of NiOx films. And for most of the inverted PSCs with NiOx HTL, the hole-extraction efficiency was limited by the unmatched valence band and too much surface defects of NiOx, causing poor performance of the device. To date, solution-based synthesizing methods and surface treatments were widely used for achieving high efficiencies of the PSCs. But the vacuum-based synthesizing methods and surface treatments are rarely reported. Herein, we developed a facile plasma post-treatment for the electron-beam evaporated NiOx to regulate its Ni3+/Ni2+ ratio and improve its electronic performance. By using O2 plasma treatment, we successfully enhanced the conductivity of the NiOx and optimized the charge-extraction capability. As a result, the all-vacuum deposited PSCs based on the O2 plasma-treated NiOx HTL achieved a champion PCE of 17.84%. This facile approach is expected to be further developed for fabricating high-efficiency PSCs on textured silicon solar cell.

Boosting near-infrared absorption properties enabled by oxygen vacancy engineering within tungsten trioxide

Tungsten-based semiconductor nanomaterials have great potential for developing energy-saving windows as a consequence of excellent shielding performance in the near-infrared (NIR) region. The performance of such nanomaterials is profoundly influenced by the the oxygen vacancies (OVs). However, the relationship between NIR absorption properties and OVs concentration has been rarely explored. In this work, the WO3-x nanosheets capable of various OVs concentration were successfully synthesized via a simple solvothermal approach, and we have carefully investigated their optical properties. Particularly, we found that the WO3-x-Pr nanosheets showed the strongest UV and NIR absorption, with the transmittance in visible region is up to 60%. Furthermore, this material is capable of the lowest temperature gap (about 11.4 °C). This work manifests that the optical performance of the tungsten (W)-based semiconductor nanomaterials is highly depended by the OVs concentration.

Characterization of intrinsic low-polyimide films studied by positron annihilation

Four kinds of polyimide (PI) films were prepared by polycondensation reaction using the pyromellitic dianhydride (PMDA) and 4, 4′-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA）as the dianhydride monomer, the p-phenylenediamine (PDA), 4-4′-diaminodiphenyl ether (ODA) and 4,4′-(Hexafluoroisopropylidene) bis(p-phenyleneoxy) dianiline (HFBDA) as the diamine monomer respectively. The incorporation of trifluoromethyl groups can effectively inhibit the formation of intermolecular and intramolecular charge-transfer complex (CTC), improve the energy gap and increase the free volume in PI, which leads to an improvement in the optical and dielectric properties in different degree for three fluorinated PI films compared with the Kapton film. The maximum transmittance in visible region reaches 90.5% and the dielectric constant at 104Hz is close to 2.0 for PI6FDA-HFPBDA film. The breakdown strength weakens because of the increase of free volume. The correlation between the dielectric and breakdown characteristics and their free volume has been explained with the help of positron lifetime spectra.

Preparation and Optical Properties of TiO2/SiO2 bilayer antireflection film

TiO2 films were deposited on monocrystalline silicon wafers with radio frequency (RF) magnetron sputtering, and the effects of O2 flow ratio on the films' stoichiometric ratio, phase composition, micromorphology and refractive index were investigated. The results showed that as O2 flow ratio increased, O/Ti molar ratio in the film increased from 1.92 to 2.04, an anatase phase was gradually formed in the film although the substrate was not intentionally heat, the surface nanoparticles became larger, and the film's refractive index decreased first and then increased continuously. And a TiO2/SiO2 bilayer antireflection film was designed and prepared on the quartz glass substrate, of which the TiO2 layer was composed of columnar particles vertically grown on the substrate, and the SiO2 layer was amorphous. This film increased substrate's average transmittance in visible region (380–780 nm) by 0.7%, and the coated substrate's maximum transmittance reached 95.9% at 505 nm wavelength, which was 2.8% higher than that of the blank substrate. The photoelectric conversion efficiency of the solar cell covered by the bilayer sample increases by 0.35% slightly and the external quantum efficiency increases by 1.08% at 500 nm.

TiO2 thin films derived by facile sol-gel method: Influence of spin rate and Al-doping on the optical and electronic properties

Titanium dioxide (TiO2) thin films with enhanced properties have been synthesized by sol-gel method and they can be used for various applications as in field-effect transistors (FETs), sensors, photovoltaics etc. The properties of TiO2 thin films were optimized by changing spin speed (1000 and 3000 rpm) and doping Al in the TiO2 lattice. The influence of spin speed and Al doping on the grain orientation and surface morphology of titania were studied using x-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Uniform, smooth and compact TiO2 thin films having tetragonal anatase phase and a band gap of 3.54 eV along with an optimum thickness and high dielectric constant of ~28 were obtained at a spin speed of 3000 rpm. These films have been previously reported as a gate dielectric layer in the fabrication of flexible ZnO:Al thin film transistor with a mobility of 4.96 cm2/Vs, therefore, the samples prepared at different spin speed could be useful for the fabrication of organic and inorganic FETs. Detailed study was performed on Al-doped TiO2 thin films. XRD and various vibrational modes noticed in the Raman spectra confirmed the formation of crystalline TiO2 films with a pure anatase tetragonal phase. A systematic shift in (101) plane in XRD and E1 g mode in Raman spectra confirms the substitutional doping of Al in the TiO2 matrix. A red shift in the band gap energy with increased transmittance in visible region was observed for the Al-doped TiO2 samples. The higher value of Urbach energy for the Al-doped samples reveals the presence of defects related to oxygen which were further studied by the photoluminescence spectra (PL). AFM images revealed compact, void free and uniform deposition of both TiO2 and TiO2: Al films. The particle size was found to be in the range of 30–40 nm and 40–100 nm for TiO2 and TiO2: Al, respectively. Enhanced electrical conductivity was observed for the Al-doped TiO2 thin films. The current Al-doped TiO2 system with enhanced optical, morphological and electrical properties could be a potential candidate in optoelectronic, sensing and photovoltaics applications.

Microstructure and local electrophysical properties of sol-gel derived (In2O3-10%SnO2)/V2O5 films

Sol-gel synthesis of thin In2O3-xSnO2 (x = 5–15 mol% SnO2) films and double-layer (In2O3-10%SnO2)/V2O5 nanostructures utilizing hydrolytically active metal alkoxoacetylacetonate complexes [M(C5H7O2)x(C4H9O)y] (M = In3+, Sn4+) and [VO(C5H7O2)2-z(C4H9O)z] as precursors was studied. Dependencies of mean coherent scattering regions (CSR) and particle size, specific resistance, work function, band gap and transmittance in visible region on tin dioxide contents in obtained In2O3-xSnO2 films were determined and attributed to changes in crystal lattice parameter and oxygen vacancies amount. For (In2O3-10%SnO2)/V2O5 bilayer thin film nanostructures, microstructural and local electrophysical properties were studied. It was shown that vanadium (V) oxide deposited on the surface of In2O3-10%SnO2 film constitutes a coating made of hemispherical clusters of about 180 nm diameter and mean height of 80 nm, with distance between clusters being roughly 100–500 nm and clusters themselves showing good conductivity.

Engineering highly transparent UV-shielding films with disassembled polydopamine oligomers as light adsorber

In this study, a highly transparent ultraviolet (UV)-shielding film was prepared by developing disassembled polydopamine (dPDA) oligomers as active UV light absorbers, followed by the incorporation into the matrix of polyvinyl alcohol (PVA) via a solvent casting method. It was shown the composite film with only 0.5 wt% of dPDA addition could barrier 99.3% of UV light (wavelength of 200–400 nm), without compromising the film transparency. Such excellent UV-shielding ability was attributed to the limited inter- and intra-molecular conjugations in dPDA oligomers which can be well dispersed in PVA matrix. Besides, the weakened molecular conjugations in dPDA led to obvious blue-shift of UV–vis absorbance, and thus strong absorbance in UV region but high transmittance in visible region. Moreover, the dPDA/PVA films exhibit higher photostability than PDA/PVA ones due to the absence of free radicals in dPDA, which was advantageous to avoid the photoaging in the long-term use under UV irradiation. This work proves the feasibility of dPDA oligomers as highly efficient light absorbers used for UV-shielding films and provides some new insights to overcome the trade-off effect between transparency and UV-shielding for preparing high-performance UV-shielding films.

Structural, raman, photo-luminescent and optical investigation of sol–gel derived Co, Al and Ni doped ZnO thin films

In this work, sol–gel spin coating route was utilized for the synthesis of undoped, Co-doped, Al-doped, and Ni-doped thin films of ZnO. XRD results show that deposited thin films possess a hexagonal lattice with preferential c-axis orientation. A reduction in lattice constants was observed owing to the substitution of Zn2+ ions by lower radius doping ions Co2+, Al3+, and Ni2+. The effect of doping is to reduce the crystallite size. Raman spectra show a characteristic peak of hexagonal ZnO at 439 cm−1. PL spectrum of all films demonstrates a UV emission ascribed to near band edge transition and a green emission band. All thin films with the transmission in visible regions above 86% are highly transparent. The doping element influenced the band gap of doped thin films.

Translucent and superhydrophobic glass for self-cleaning and acid rain-restraining

Translucent and superhydrophobic glass surface was fabricated by a NH4F-assisted in-situ growth and post-modification process. Vertical and interconnected layered double hydroxide (LDH) nanosheets were built on the glass surface to enhance surface roughness, and then modified with stearic acid (SA) to reduce the surface energy. The water contact angle (WCA) and water sliding angle (WSA) of the prepared glass was 167° and 2°, respectively, exhibiting the excellent water-repellency and self-cleaning ability. The transparency of the prepared glass was measured by UV–Vis spectrophotometer, and the transmittance in visible region was ranged from 68% to 77.8%. The prepared glass possessed outstanding ability to withstand physical and chemical damage, such as sandpaper abrasion, tape-peeling and acid/base immersion. In addition, the superhydrophobic glass had good environmental adaptability, which can resist UV irradiation and acid raindrop impact. Consequently, the obtained translucent and superhydrophobic glass can be applied in various fields, such as self-cleaning traffic indicators, wind screens, self-cleaning windows and dust-free solar panels.

Influence of aluminum doping on microstructure, optical and electrical properties of c axis oriented zinc oxide nano films prepared by nebulizer spray pyrolysis technique

Transparent conducting aluminum-doped ZnO thin films have been prepared by nebulizer spray pyrolysis technique for different doping concentrations on glass substrates. X-ray diffraction patterns reveal that all the films are polycrystalline of hexagonal structure with c–axis orientations. Atomic force microscopy (AFM) images noticed that the films have a uniform surface morphology consist spike shaped particles and low surface roughness. The optical transmittance in visible region was escalated from 85 to 93% and optical band gap of thin films is also improved from 3.27 to 3.37 eV. Photoluminescence spectra show mainly five emissions peaks and a blue shift observed in UV emission peak. Hall Effect measurements show that the prepared films having n-type conductivity with low resistivity and high carrier concentrations.

Synthesis and characterization of Co and Ga co-doped ZnO thin films as an electrode for dye sensitized solar cells

Using a time efficient and cost effective approach so called sol‒gel dip coating route, we deposited thin films of ZnO and 1% Co & (0%, 0.5%, 1%, and 1.5%) Ga co-doped ZnO on the fluorine doped tin oxide substrates. All the films exhibited hexagonal wurtzite structure. X-rays study revealed that crystallite size increased with increase of doping. Optical parameters like absorbance, transmittance, refractive index, band gap, extinction coefficient and dielectric constants were measured using UV–Vis spectroscopy and it has been noticed that doping resulted in reduction of band gap. It has also been observed that, the films prepared with 1% Co & 1% Ga co-doped ZnO have comparatively smaller band gap and thus have high refractive index and high transmittance in visible region. The calculation of different electrically important factors for instance, high current density, small open circuit voltage, efficiency and fill factor revealed that co-doped ZnO with 1% Co and 1% Ga has relatively high efficiency of 2.43% and thus shows the potential of this composition as an electrode for solar cell devices.

Potential low powered smart window coating using a stoichiometrically downgraded vanadium oxide thin film structure

With a metal to insulator transition (MIT) temperature of ∼68 °C to 70 °C, which is close to room temperature (RT), vanadium oxide (VO2) has piqued interest in research communities for several applications, such as Mott-transistors and smart windows. This unique characteristic and multi-faceted application of VO2 makes it ideal for several fields, from consumer electronics to defense applications. However, despite this advantage over several other materials, VO2 has some serious shortcomings. In this paper, we attempt to address these issues, such as higher than RT transition temperature, metastability of the material, and its need for a separate heater layer to trigger the MIT, by using a stoichiometrically downgraded multi-layered structure that can both demonstrate the MIT property and serve as an embedded heater layer. This eliminates the need to use a system with a different material such as aluminum-doped zinc oxide. By using the multi-layered structure, we were able to achieve a transition temperature of ∼48 °C, which is ∼22 °C lower than the transition temperature of bulk VO2 films. We also noted a reduction of over 50% in transmission in the infra-red region by application of less than 15 V, as well as an enhancement of ∼10% in the visible region transmission beyond the MIT temperature, which demonstrates the potential of this structure to be used as an energy-efficient smart window device.

Effect of post-annealing in oxygen environment on ITO thin films deposited using RF magnetron sputtering

This work demonstrated the effect of post-annealing on electrical and optical characteristics of indium tin oxide (ITO) thin films. ITO with 100 nm thickness was successfully deposited using radio frequency (RF) magnetron sputtering in oxygen-free environment on sodalime glass substrate without substrate heating. Post-annealing treatment was carried out on ITO thin films in oxygen environment. Different annealing temperatures were studied on the films from 300°C up to 600 °C. The annealing time and oxygen flow rate were kept constant. As the annealing temperature increase, the structure of the thin film’s changes from amorphous to polycrystalline which lead to the effect of enhanced hall mobility. Annealing temperature strongly influence the optical transmission in visible region. It leads to higher transmittance of ITO thin films and is suitable for a blue light emitting diode (LED) application. In addition, higher annealing temperature also enhances film electrical performance. Further characterization of the deposited films was done using hall measurement, UV-Vis spectrophotometer and atomic force microscopic (AFM) to show the improvement on their electrical and optical characteristic. The optical and electrical characteristics of the films have been compared with each other.

Photoresponse properties and energy gap of CsPbBr3–CsPb2Br5 compound thin film prepared by one-step thermal evaporation method

We proposed the preparation of the compound thin film of CsPb2Br5 and CsPbBr3 perovskites via thermal evaporation method with post-annealing. The optical absorption, energy gap, and photoresponse properties of the compound thin films were investigated. Over 90% transmittance in visible region of 550–700 nm was obtained, and the energy gap of thin film was found to be in the range of 2.28–2.35 eV. Using 405 nm laser, the compound thin film showed obvious response dependence on light power. Even if the large conductive channel of 1 mm × 100 μm was used, thin film possessed still good cycle characteristics, available responsivity, and a rapid response at applying 5 V.

Effect of wavelengths on the structure, morphology and optoelectronic properties of cadmium sulfide thin films by laser assisted chemical bath deposition

Laser assisted chemical bath deposition (LACBD) is an interesting technique to synthesize semiconductor thin films. The effects of three laser wavelengths (445, 457 and 532 nm) on the structure, composition, morphology and optoelectronic properties of cadmium sulfide (CdS) thin films by LACBD are presented. Structural analysis of the thin films confirmed their polycrystalline nature. The surface composition specifics and chemical states of Cd and S were studied by X-ray photoelectron spectra. The topography and roughness of the films were explored by atomic force microscopy. The films exhibited high transmittance in visible region with 2.5 eV bandgap. All the samples showed photocurrent response under irradiation for white light as well as selected wavelengths of visible light emitting diodes from which the electrical properties were evaluated. The results showed that the laser irradiation by various wavelengths was effective in modification of surface topography and optoelectronic properties of the polycrystalline CdS thin films.