Enhancement Of Optical Transmittance Research Articles

Ultraviolet photoconductivity and photoluminescence properties of spray pyrolyzed ZnO nanostructure: Effect of deposition temperature

The current investigation focuses on the influence of substrate temperature on Zinc Oxide (ZnO) thin films synthesized on glass substrates using 0.1 M precursor solution by low-cost spray pyrolysis technique. The x-ray diffraction peaks matched the hexagonal wurtzite structure of ZnO with the highest intensity along the (1 0 1) plane. Estimated the crystallite size, dislocation density, micro-strain, and the number of crystallites in the deposits using X ray diffraction (XRD) data. The crystallinity of the films deposited at 450 °C was maximum. Fibrous surface morphology is altered by varying the deposition temperature. The enhancement of optical transmittance and energy bandgap of the deposits with deposition temperature. The reduction of Urbach energy with an increase in the substrate temperature confirmed the improvement of crystallinity. The photoluminescence study revealed peaks associated with electron-hole pair recombination, zinc, and oxygen-related defects. The samples deposited at 450 °C showed minimum defects. Commission Internationale de l'éclairage (CIE) chromaticity diagram showed white light emission for sample deposited at 450 °C with the color temperature equal to 5378 °C which is agreeing with the temperature of a normal white light source. Improvement of free carrier concentration and n-type conductivity due to the enhancement of crystallinity was observed. ZnO thin films deposited at 450 °C showed maximum photocurrent when illuminated with UV light and faster rise and fall of photo resistance due to the improvement in the crystallinity and carrier concentration. The maximum photosensitivity was observed for the samples synthesized at 450 °C. Hence the ZnO thin films deposited at 450 °C can be used as ultraviolet photodetector material.

Investigation on the structural and optical properties of copper doped NiO nanostructures thin films

Abstract In this research, copper is doped NiO nanostructures thin films by using various doping compositions (2, 4, 6 & 8%) have been prepared by chemical spray pyrolysis technique at a temperature of (400 °C). The optical, morphological and structural properties were investigated using UV–visible spectrophotometry, X-Ray diffraction (XRD) and atomic force microscopy (AFM). The results of (XRD) showed that all the prepared films are polycrystalline in nature with cubic structure with a strong (1 1 1) preferred orientation and the average crystallite size decreased with increase copper concentration, while the results of (AFM) indicate that the roughness of the surface decrease with increase doping. Enhancement of optical transmittance with doping decrease in the range (300–900 nm) was observed, and the absorption coefficient increased by increasing doping ratio, while the optical energy gap for allowing direct transmission decreased in the range (3.31 to 2.94 eV).

Enhancement of optical transmittance and electrical resistivity of post-annealed ITO thin films RF sputtered on Si

This paper reports on the enhancement of optical transmittance and electrical resistivity of indium tin oxide (ITO) transparent conductive oxides (TCO) deposited by radio frequency (RF) sputtering on Si substrate. Post-annealing was conducted on the samples at temperature ranges of 500–700 °C. From X-ray diffraction analysis (XRD), ITO (2 2 2) peak was observed after post-annealing indicating crystallization phase of the films. From UV–vis measurements, the ITO thin film shows highest transmittance of more than 90% at post-annealing temperature of 700 °C as compared to the as-deposited thin films. From atomic force microscope (AFM), the surface roughness becomes smoother after post-annealing as compared to the as-deposited. The lowest electrical resistivity for ITO sample is 6.68 × 10−4 Ω cm after post-annealed at 700 °C that are contributed by high carrier concentration and mobility. The improved structural and surface morphological characteristics helps in increasing the optical transmittance and reducing the electrical resistivity of the ITO thin films.

Optical Transmittance Enhancement of Flexible Copper Film Electrodes with a Wetting Layer for Organic Solar Cells.

The development of highly efficient flexible transparent electrodes (FTEs) supported on polymer substrates is of great importance to the realization of portable and bendable photovoltaic devices. Highly conductive, low-cost Cu has attracted attention as a promising alternative for replacing expensive indium tin oxide (ITO) and Ag. However, highly efficient, Cu-based FTEs are currently unavailable because of the absence of an efficient means of attaining an atomically thin, completely continuous Cu film that simultaneously exhibits enhanced optical transmittance and electrical conductivity. Here, strong two-dimensional (2D) epitaxy of Cu on ZnO is reported by applying an atomically thin (around 1 nm) oxygen-doped Cu wetting layer. Analyses of transmission electron microscopy images and X-ray diffraction patterns, combined with first-principles density functional theory calculations, reveal that the reduction in the surface and interface free energies of the wetting layers with a trace amount (1-2 atom %) of oxygen are largely responsible for the two-dimensional epitaxial growth of the Cu on ZnO. The ultrathin 2D Cu layer, embedded between ZnO films, exhibits a highly desirable optical transmittance of over 85% in a wavelength range of 400-800 nm and a sheet resistance of 11 Ω sq-1. The validity of this innovative approach is verified with a Cu-based FTE that contributes to the light-to-electron conversion efficiency of a flexible organic solar cell that incorporates the transparent electrode (7.7%), which far surpasses that of a solar cell with conventional ITO (6.4%).

Electron-beam irradiation induced optical transmittance enhancement for Au/ITO and ITO/Au/ITO multilayer thin films

Electron beam (EB) irradiation experiments on Au/ITO and ITO/Au/ITO multilayer thin films are reported. The structure and the optical-electrical properties of the samples were investigated by X-ray diffraction, atomic force microscopy, four-point probe resistivity measurement system, and UV–vis-NIR double beam spectrometer, respectively. Those results show that the EB irradiation has the effects of improving the crystalline of samples, widening the optical band gap of both thin films, reducing the sheet resistance, and improving the transmittance of samples.

Manipulation of Optical Transmittance by Ordered-Oxygen-Vacancy in Epitaxial LaBaCo2O5.5+δ Thin Films.

Giant optical transmittance changes of over 300% in wide wavelength range from 500 nm to 2500 nm were observed in LaBaCo2O5.5+δ thin films annealed in air and ethanol ambient, respectively. The reduction process induces high density of ordered oxygen vacancies and the formation of LaBaCo2O5.5 (δ = 0) structure evidenced by aberration-corrected transmission electron microscopy. Moreover, the first-principles calculations reveal the origin and mechanism of optical transmittance enhancement in LaBaCo2O5.5 (δ = 0), which exhibits quite different energy band structure compared to that of LaBaCo2O6 (δ = 0.5). The discrepancy of energy band structure was thought to be the direct reason for the enhancement of optical transmission in reducing ambient. Hence, LaBaCo2O5.5+δ thin films show great prospect for applications on optical gas sensors in reducing/oxidizing atmosphere.

Mechanical Strength and Broadband Transparency Improvement of Glass Wafers via Surface Nanostructures.

In this study, we mechanically strengthened a borosilicate glass wafer by doubling its bending strength and simultaneously enhancing its transparency using surface nanostructures for different applications including sensors, displays and panels. A fabrication method that combines dry and wet etching is used for surface nanostructure fabrication. Specifically, we improved the bending strength of plain borosilicate glass by 96% using these surface nanostructures on both sides. Besides bending strength improvement, a limited optical transmittance enhancement of 3% was also observed in the visible light wavelength region (400–800 nm). Both strength and transparency were improved by using surface nanostructures of 500 nm depth on both sides of the borosilicate glass without affecting its bulk properties or the glass manufacturing process. Moreover, we observed comparatively smaller fragments during the breaking of the nanostructured glass, which is indicative of strengthening. The range for the nanostructure depth is defined for different applications with which improvements of the strength and transparency of borosilicate glass substrate are obtained.

Enhancement of Optical Transmittance of Polymer-Dispersed Liquid Crystal Cells

Enhancement of optical transmittance of polymer-dispersed liquid crystal (PDLC) cells was investigated by introducing a modification into the substrates. Surface treatment by rubbing was performed on both network-type and droplet-type PDLCs to investigate the effect on the optical transmittance of the cells. Differences in the transmittance of the PDLC in the polymer matrix were observed by introducing rubbing effect on network-type PDLC but not on droplet-type PDLC. These phenomena might be used to distinguish the application field of both types of PDLC cells by enhancing optical transmittance and scattering properties.

Nanostructured Antireflection Coatings for Optical Detection and Sensing Applications

ABSTRACTOptical components such as lenses, glass windows, and prisms are subject to Fresnel reflection due to the mismatch between the refractive indices of the air and glass. An optical interface layer, i.e., antireflection (AR) layer, is needed to eliminate this unwanted reflection at the air/glass interface. Nanostructured broadband and wide-angle AR structures have been developed using a scalable self-assembly process. Ultra-high performance of the nanostructured AR coatings has been demonstrated on various substrates such as quartz, sapphire, polymer, and other materials typically employed in optical lenses. AR coatings on polycarbonate lead to optical transmittance enhancement from approximately 90% to almost 100% for the entire visible, and part of the near-infrared (NIR), band. The AR coatings have also been demonstrated on curved surfaces. AR coatings on n-BK7 lenses enable ultra-high light transmittance for the entire visible, and most of the NIR, spectrum. Nanostructured oxide layers with step-graded index profiles, deposited onto the optical elements of an optical system, can significantly increase sensitivity, and hence improve the overall performance of the system.

Synthesis and characterization of amorphous aluminum oxide thin films prepared by spray pyrolysis: Effects of substrate temperature

Amorphous and non-crystalline aluminum oxide thin films have been deposited on glass substrate by spray pyrolysis method. The structural, morphological and optical properties were investigated using X-Ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-visible spectrophotometry. For two specific molarities (0.15M and 0.25M), substrate temperature was varied between 250°C, 350°C, 500°C, and 550°C. The XRD results exhibited dominant amorphous nature for all samples as expected, whereas SEM and AFM showed the presence of substrate temperature effects on alumina thin film properties. Enhancement of optical transmittance with temperature increase was observed. Using the transmittance data other optical quantities namely absorption coefficient, optical band gap, refractive index and extinction coefficient, dielectric constants, volume and surface energy loss functions and optical conductivity were determined. It was also observed that the volume energy loss (VELF) increases more than the surface energy loss (SELF).

Optical transmittance enhancement and bandgap widening of ZnO:Al powders by W codoping

(Al, W)-codoped ZnO powders with a constant molar ratio of Zn:Al (99:1) and various molar ratios of W:Al (0–0.02) were synthesized by a sol–gel process and characterized by X-ray diffraction, field emission scanning electron microscopy, and UV–vis and luminescent spectrophotometry. The experiments indicated that the powders illustrated increased c-orientation and a decreased average particle size with increasing W content. The W doping also resulted in the enhancement of transmittance in the UV–vis light range and the widening of the bandgap. Optimal efficiency appeared at molar ratio of W:Al = 0.01. Moreover, the W doping led to the formation of a new emission center and the enhancement of the emissions in range of visible light.

Modulation of surface plasmons coupling for enhancement of optical transmittance of silver-coated alkaline-earth metal films

We enhanced the optical transmittance of silver-coated alkaline-earth metal films by modulation of surface plasmons (SPs) coupling. The result indicates that the optical transmittance of a metal film is controlled by the SPs coupling at the interface of the metal with a dielectric substrate. Because the SPs originate from the coupling between the free charge at the surface of the metal and the incident light, there exists the SPs coupling in an Ag layer with the dielectric substrate. These SPs lead to longitudinal surface charge density fluctuations that propagate along the substrate/Ag interface, resulting in the decreased transmittance property (47.9% in the visible region) of the 10 nm thick Ag layer on the dielectric substrate. Because both alkaline-earth metal and Ag have negative dielectric constants, the incident light cannot induce the SPs in the alkaline-earth metal/Ag double layer. Thus, inserting a thin alkaline-earth metal layer between Ag and the dielectric substrate could modulate the SPs coupling at the Ag/substrate interface and, hence, the optical transmittance of alkaline-earth metal/Ag films. Both alkaline-earth metal and Ag could be formed by thermal evaporation and in situ synchrotron radiation photoelectron spectroscopy results showed that the thermally evaporated alkaline-earth metal (Ca) film is composed of metallic (Ca) and metal-oxide (CaO) components. It is found that the SPs modulation optimized alkaline-earth metal/Ag (10 nm/10 nm) film has obtained a higher optical transmittance (69.8%) in the visible region than that of an Ag layer. This led to the enhanced maximum luminance of organic light emitting diodes with the alkaline-earth metal/Ag electrode from 24 300 cd m−2 to 32 700 cd m−2.

Improvement of Quantum Efficiency of Amorphous Silicon Thin Film Solar Cells

AbstractThe enhancement of optical transmittance at the air/glass interface of amorphous silicon thin film solar cells was shown by application of a nanoporous polymethyl methacrylate (PMMA) antireflection (AR) coating. The PMMA coating was prepared by spin coating of PMMA solution in chloroform in the presence of a small amount of nonane. Because of the difference of the vapor pressure of chloroform and nonane, phase separated structure formed after complete evaporation of both of them during spin coating process. The Corning 1737 glass with the AR coating has high transmittance near 95% from 450-1100nm wavelengths. The amorphous silicon solar cells with the nanoporous PMMA AR coating realize an improvement in quantum efficiency (QE) up to 4% in 450-650nm spectral regions.