ZnO-coated Glass Substrates Research Articles

Modulation of Sn concentration in ZnO nanorod array: intensification on the conductivity and humidity sensing properties

Tin (Sn)-doped zinc oxide (ZnO) nanorod arrays (TZO) were synthesized onto aluminum-doped ZnO-coated glass substrate via a facile sonicated sol–gel immersion method for humidity sensor applications. These nanorod arrays were grown at different Sn concentrations ranging from 0.6 to 3 at.%. X-ray diffraction patterns showed that the deposited TZO arrays exhibited a wurtzite structure. The stress/strain condition of the ZnO film metamorphosed from tensile strain/compressive stress to compressive strain/tensile stress when the Sn concentrations increased. Results indicated that 1 at.% Sn doping of TZO, which has the lowest tensile stress of 0.14 GPa, generated the highest conductivity of 1.31 S cm−1. In addition, 1 at.% Sn doping of TZO possessed superior sensitivity to a humidity of 3.36. These results revealed that the optimum performance of a humidity-sensing device can be obtained mainly by controlling the amount of extrinsic element in a ZnO film.

Improvements in external quantum efficiency of electrochemically constructed n-ZnO/p-Cu2O photovoltaic devices by rapid thermal annealing

Thin-film ZnO/Cu2O photovoltaic devices were prepared by electrochemical deposition in aqueous solutions, and significant improvements in the photovoltaic performances, especially external quantum efficiency (EQE), were achieved by rapid thermal annealing (RTA). ZnO were electrodeposited on Ga: ZnO-coated glass substrates from solutions containing zinc nitrate, and Cu2O were electrodeposited on the ZnO layer from solutions containing copper acetate and lactic acid. The photovoltaic performances were evaluated after annealing the ZnO/Cu2O layers at varying temperatures of 423–573 K under vacuum for 60 min, and a high EQE of nearly 100% was demonstrated by RTA at 423 K under vacuum. To elucidate the improvement effect of the RTA, structural characterizations were carried out with XRD and FESEM, and the optical and electrical properties were examined by UV–vis absorption spectroscopy and Hall effect measurements, respectively. The improvements in EQE was mainly attributed to the lessening of scattering defects in the light-absorbing Cu2O layer such as lattice dislocations and grain boundaries, which improved the charge collection efficiency. The photovoltaic performances deteriorated at elevated temperatures above 523 K due to the generation of small Cu particles on the Cu2O surface, which is associated with the generation of nanopores in the Cu2O bulk.

Synthesis and characterization of ZnO micro-rods and temperature-dependent characterizations of heterojunction of ZnO microrods/CdTe and ZnO microrods/ZnTe structures

ZnO microrods were fabricated on ZnO-coated SnO2 glass substrates by spray pyrolysis method. To obtain p-n heterojunction, p type CdTe and ZnTe layers were deposited on ZnO microrods. The structural characterizations demonstrated that ZnO microrods have a hexagonal wurtzite structure with vertically aligned rod morphology. Additionally, hexagonal rod geometry was compressed by coating CdTe layer on micro-sized ZnO rods. The diode type rectifying behaviour of ZnO microrods/CdTe and ZnO microrods/ZnTe heterojunctions have been carried out and the electrical characteristics of both devices have been analyzed with current-voltage measurements as a function of temperature. Although the mismatch between ZnO and ZnTe, the ZnO microrods/ZnTe heterojunction showed good rectifying behaviour at all temperatures. According to the our findings, both ideality factor n and barrier heightΦb are temperature-dependent due to the deviation from pure thermionic emission theory and inhomogeneity at the interface of ZnO-CdTe and ZnO-ZnTe.

Fabrication of hierarchical Sn-doped ZnO nanorod arrays through sonicated sol−gel immersion for room temperature, resistive-type humidity sensor applications

Hierarchical tin (Sn)-doped zinc-oxide (ZnO) nanorod arrays (SZO) were deposited onto Al-doped ZnO-coated glass substrate by using a sonicated sol–gel immersion method for resistive-type humidity sensor applications. X-ray diffraction patterns revealed that the deposited SZO arrays exhibit a wurtzite structure. SZO possessed smaller average diameter, crystallite size, and thickness than the undoped sample did. The SZO film also exhibited compressive strain and tensile stress values of −0.033% and 77MPa, respectively. Our result showed the sensitivity of the SZO based-sensor improved compared with that of the undoped ZnO, with values of 3.41 and 1.41 at 40% to 70% RH and 70% to 90% RH, respectively. The response and recovery times of the SZO based humidity sensor improved to 230 and 30s, respectively. All these results indicated that SZO had high potential for humidity-sensor applications.

Cu(In,Ga)Se2 superstrate solar cells: prospects and limitations

AbstractSuperstrate solar cells were prepared by thermal evaporation of Cu(In,Ga)Se2 onto ZnO coated glass substrates. For the first time, photo‐conversion efficiencies above 11% were reached without the necessity of additional light soaking or forward biasing of the solar cell. This was achieved by modifying the deposition process as well as the sodium doping. Limitations of the superstrate device configuration and possible ways to overcome these were investigated by analyzing the hetero‐interface with electron microscopy and X‐ray photoemission spectroscopy measurements, combined with capacitance spectroscopy and device simulations. A device model was derived that explains how on the one hand the GaOx, which forms at the CIGSe/ZnO interface, reduces the interface recombination. On the other hand how it limits the efficiency by acting as an electron barrier at the hetero‐interface presumably because of a high density of negatively charged acceptor states like CuGa. The addition of sodium enhances the p‐type doping of the absorber but also increases the net doping within the GaOx. Hence, a trade‐off between these two effects is required. The conversion efficiency was found to decrease over time, which can be explained in our model by field‐induced diffusion of sodium cations out from the GaOx layer. The proposed device model is able to explain various effects frequently observed upon light soaking and forward biasing of superstrate devices. Copyright © 2014 John Wiley & Sons, Ltd.

Studies on the Controlling of the Microstructural and Morphological Properties of Al Doped ZnO Thin Films Prepared by Hydrothermal Method

Al doped ZnO (AZO) thin films were prepared on ZnO coated glass substrates by hydrothermal synthesis technique using aqueous solutions containing zinc nitrate hexahydrate, ammonium hydroxide, and different sodium citrate concentrations at 60 °C for 6 h. The effects of different trisodium citrate concentrations on the microstructural, crystallinity, morphological, optical, and chemical properties of thin films were investigated. X-ray diffraction studies showed that the AZO thin films were grown as a polycrystalline wurtzite hexagonal phase with a c-axis preferred orientation and without an unwanted second phase regardless of trisodium citrate concentrations. The thickness and grain sizes of AZO thin films decreased with increasing trisodium citrate concentration. The microstructure of AZO thin films was changed from flat to needle shaped and the morphology was smoother with increasing trisodium citrate concentrations. The AZO thin films have a high transmittance in the visible region ranging from 75 to 85% and a sharp edge from 366 to 374 nm.

VO<sub>2</sub> Thin Films Deposited on ZnO<sub> </sub>Buffer Layer

Vanadium oxide thin films have been deposited on glass and ZnO-coated glass substrates by reactive RF-magnetron sputtering deposition at different substrate temperature. The introduction of ZnO buffer layer could increase the transmittance. The buffer layer ZnO could lead to the increase of the crystallinity quality of VO2 films and substrate temperature could be decreased to 100°C for the obtaining of polycrystalline VO2 structure. The structure of VO2/ZnO/glass is considered to be potentially applicable to ‘‘smart windows’’ of high total energy efficiency in architectures or automobiles. .

Vanadium Dioxide Thin Films Deposited on ZnO Buffer Layer for Smart Thermochromic Glazing of Windows

Vanadium oxide thin films have been deposited on glass and ZnO-coated glass substrates by reactive RF-magnetron sputtering deposition at different substrate temperature. The introduction of ZnO buffer layer could increase the transmittance. The buffer layer ZnO could lead to the increase of the crystallinity quality of VO2 films and substrate temperature could be decreased to 100°C for the obtaining of polycrystalline VO2 structure. The structure of VO2/ZnO/glass is considered to be potentially applicable to smart windows of high total energy efficiency in architectures or automobiles.

Development of textured ZnO-coated low-cost glass substrate with very high haze ratio for silicon-based thin film solar cells

Zinc oxide (ZnO) films with a very high haze ratio and low resistivity were developed on soda–lime glass substrate by using reactive ion etching (RIE) treatment with carbon tetrafluoride (CF4) to modify the substrate surface morphology before the deposition of ZnO films. We found that the surface morphology of the ZnO films deposited by metal organic chemical vapor deposition (MOCVD) technique could be modified by varying the glass treatment conditions and the gas pressure was a key parameter. With increasing glass-etching pressure, the surface morphology of the ZnO films changed from conventional pyramid-like single texture to greater cauliflower-like double texture, leading to significant increases in root mean square roughness and haze ratio of the films. By employing the developed high-haze ZnO films as a front transparent conductive oxide (TCO) layer in microcrystalline silicon solar cells, an enhancement in the quantum efficiency in the long-wavelength region has been achieved. Experimental results have verified that our unique and original glass etching treatment is a simple and effective technique to improve the light-scattering properties of the ZnO films while preserving their good transparency and electrical properties. Thus, the ZnO films deposited on etched soda–lime glass have a high potential for the use as a front TCO layer in thin-film Si solar cells.

Electrical and Structural Properties of ZnO Films Grown from Aqueous Solutions

ZnO films with a preferential c-axis orientation have been deposited on ZnO-coated glass substrates by using aqueous solutions containing ZnCl2 and ZnF2. The ZnF2 ratio [ZnF2/(ZnCl2+ZnF2)] affects electrical, optical, and structural properties of the ZnO films. Except for the ZnO film grown at the ZnF2 ratio of 30%, the ZnO films had a transmittance above 80% in the range of 550–1000 nm. Carrier concentration of the ZnO films increased with increasing ZnF2 ratio, reaching the maximum value at the ZnF2 ratio of 10%. Resistivity of the ZnO films decreased with an increase in the carrier concentration. The resistivity, carrier concentration, and Hall mobility of the ZnO film grown at the ZnF2 ratio of 10% were 5.8×10-3 Ω cm, 1.0×1020 cm-3, and 11 cm2 V-1 s-1, respectively.

Radial junction amorphous silicon solar cells on PECVD-grown silicon nanowires

Constructing radial junction hydrogenated amorphous silicon (a-Si:H) solar cells on top of silicon nanowires (SiNWs) represents a promising approach towards high performance and cost-effective thin film photovoltaics. We here develop an all-in situ strategy to grow SiNWs, via a vapour–liquid–solid (VLS) mechanism on top of ZnO-coated glass substrate, in a plasma-enhanced chemical vapour deposition (PECVD) reactor. Controlling the distribution of indium catalyst drops allows us to tailor the as-grown SiNW arrays into suitable size and density, which in turn results in both a sufficient light trapping effect and a suitable arrangement allowing for conformal coverage of SiNWs by subsequent a-Si:H layers. We then demonstrate the fabrication of radial junction solar cells and carry on a parametric study designed to shed light on the absorption and quantum efficiency response, as functions of the intrinsic a-Si:H layer thickness and the density of SiNWs. These results lay a solid foundation for future structural optimization and performance ramp-up of the radial junction thin film a-Si:H photovoltaics.

Zn incorporation and (CuIn) 1− xZn 2 xSe 2 thin film formation during the selenization of evaporated Cu and In precursors on Al:ZnO coated glass substrates

CuInSe 2 thin films with typical 1.0 eV gap energy and tetragonal chalcopyrite structure have been obtained on soda–lime glass substrates by the reaction of sequentially evaporated Cu and In layers with elemental selenium vapor, at 500 °C in flowing Ar. When analogous deposition and reaction processes were performed on Al:ZnO coated glasses, some increment in the band gap energy and diminution in the crystalline interplanar spacings have been detected for the resulting films with an extent that depends on the Cu/In atomic ratio of the evaporated precursor layers. This fact has been related to Zn incorporation into the selenized film, with quaternary (CuIn) 1− x Zn 2 x Se 2 compound formation that is influenced by the presence of copper selenide phases during the reaction process. Such deductions are supported by the optical, structural and compositional characterizations that have been performed comparatively on samples prepared by selenization of evaporated metallic precursors with two different Cu/In ratios (0.9 and 1.1) on bare and Al:ZnO coated glass substrates.

Effects of thermal annealing on the performance of Al/ZnO nanorods/Pt structure ultraviolet photodetector

Abstract ZnO nanorod arrays were fabricated on ZnO coated glass substrate by hydrothermal method. Schottky barrier ultraviolet photodetectors (PDs) were obtained by sputtering Pt electrode and evaporating Al electrode on the top of ZnO nanorod arrays with thermal treatment. It is illustrated that Schottky contacts at the electrode/ZnO NRs interface were formed at the annealing temperature of 300 °C and above. When annealing temperature was up to 300 °C, the performance of the PDs was improved with the great decrease of response and recovery times. At the forward bias of 2 V, the Schottky contact PDs showed the biggest responsivity and the best detectivity at the annealing temperature of 300 °C. For annealing temperature at 300 °C and above, the responsivity decreases with increasing annealing temperature and the ratio of detectivity ( D 254 * to D 546 * ) was calculated as high as 10 3 for all PDs annealed at 300 °C and above.

UV detecting properties of hydrothermal synthesized ZnO nanorods

The photoresponse behavior of one-dimensional ZnO nanorods grown on ZnO-coated glass substrates via a wet-chemical route at low temperature of 70 °C was investigated. The morphology, structure, composition and chemical state of the prepared nanostructures were characterized by SEM, AFM, XRD and XPS measurements, respectively. The ZnO 1D nanostructures were found to have a hexagonal crystalline structure and grown along the [0 0 1] direction. The nanorods were about 1 μm in length and lower than 100 nm in diameter. The changes in photoresponse of the ZnO nanorods were investigated under different powers of UV illumination and it was also shown that the nanorods have a high sensitivity to UV light. The study suggested that the photoresponse originated from bulk and surface related processes. It is believed that the synthesized ZnO nanorods can be potentially useful in the designing of 1D ZnO-based optoelectronic devices.

Structural and electrical properties of Cu2O thin films deposited on ZnO by metal organic chemical vapor deposition

Cu 2 O thin films were deposited on ZnO coated glass substrates by metal organic chemical vapor deposition from copper(II) hexafluoroacetylacetonate [Cu(C5HF6O2)2], oxygen gas, and water vapor. The dependence of the structural and electrical properties of Cu2O films on deposition temperature and film thickness was investigated. X-ray diffraction showed that Cu2O thin films grow on ZnO with preferred (220)Cu2O∥(0002)ZnO orientation. The grain size and stress in Cu2O films increase with increasing substrate temperature but decrease with increasing film thickness. The carrier mobility increases with increasing grain size indicating that the carrier transport is limited by scattering from the grain boundaries. Single-phase epitaxial p-type Cu2O films with hole mobilities exceeding 30 cm2/V s are obtained at a deposition temperature of 400 °C.

Formamide driven synthesis of well-aligned ZnO nanorod arrays on glass substrate

A cost effective, low-temperature approach has been developed for the large-area deposition of ZnO nanorod/nanotube arrays on a ZnO coated glass substrate by the natural oxidation of zinc metal in formamide/water mixtures. The two-step seed deposition and wet-chemical approach exhibited well-controlled growth of highly oriented and densely packed ZnO nanorod/nanotube arrays with large-area homogeneity and uniform morphologies. In order to investigate the quality and alignment of ZnO nanorod arrays grown on the ZnO seed layer coated substrate, three different methods of ZnO coating have been deposited by ultrahigh vacuum evaporation system, DC sputtering and RF sputtering, respectively. Our results showed that the ZnO seed layer grown by RF sputtering resulted in high quality ZnO nanorod arrays.

Influence of RTA treatment on the physical properties of well-aligned ZnO nanorods

Well-aligned zinc oxide (ZnO) nanorod structures were grown on ZnO-coated (seed layer) glass substrates using a simple and low-cost aqueous solution method at a growth temperature of ∼70 °C. The physical properties were examined at room temperate using appropriate techniques. After preliminary analysis, the structures were heat treated at different temperatures varying from 300 to 800 °C using the rapid thermal annealing technique under N 2 environment for 1 min and investigated the influence of annealing effect on their physical properties. The as-grown ZnO nanorods are slightly zinc-rich in nature and exhibited hexagonal wurtzite structure. These nanorods are uniformly grown along the [0 0 1] direction and their average length and diameter are found to be ∼1.0 μm and ∼85 nm, respectively. While increasing annealing temperature, the oxygen content and crystallinity of the ZnO nanorods increased up to 600 °C, and above this temperature, the oxygen content increased continuously whereas the crystallinity of the nanorods decreased. The electrical resistivity of nanostructures slightly increased with the increase of annealing temperature probably due to the damage in their columnar structure.

Structural and opto-electronic properties of transparent conducting (2 2 2)-textured Zr-doped In 2O 3/ZnO bilayer films

5 wt% Zr-doped In 2O 3 (Zr-In 2O 3) films with thicknesses from 85 to 210 nm were grown on the 80 nm-thick ZnO-coated glass substrates at 160 °C by rf sputtering. The microstructures of the Zr-In 2O 3/ZnO bilayer films were studied using X-ray diffraction and atomic force microscopy. The ZnO buffer layers on the glass substrates exhibit (0 0 2) preferred orientation. The Zr-In 2O 3 films have highly (2 2 2)-textured structures on the ZnO-coated glass substrates. The electrical characteristics of Zr-In 2O 3 films are improved by lattice modulation with ZnO buffering. The resistivity is lowest 3.02×10 −4 Ω cm for the 210 nm-thick Zr-In 2O 3 film on the ZnO-coated glass. The average transmittance in visible wavelength region is 83–86% for Zr-In 2O 3/ZnO bilayers with various Zr-In 2O 3 film thicknesses of 85–210 nm. The low-temperature processes of Zr-In 2O 3/ZnO bilayer films on the glass substrates have potential for application to opto-electronic devices.

Growth and interconversion of ZnO nanostructure films on different substrates

Hexagonal c-axis oriented ZnO nanorod (NR) arrays were grown on ZnO-coated glass substrates by chemical bath deposition (CBD). By varying the concentration of the precursor solutions, NRs’ mean diameter was controlled from about 100–400 nm. With increasing the growing time, the morphology of as-synthesized ZnO NRs evolved: the top center of the ZnO NRs was eroded into volcano-like structures which developed into ZnO nanotubes (NT) and finally the ZnO NTs split to form ZnO nanosheets (NS). We have also introduced Al to the fabrication of some different ZnO nanostructures: on Al substrate, freestanding ZnO NSs formed a flower-like structure at the early growing period and these ZnO NSs reassembled into ZnO NTs as growing time increased; while on ZnO-coated glass substrate with an Al foil dipped in the growing precursor solution ZnO NR–NS composited arrays were synthesized.

Electrical properties of ZnO/Au/ZnS/Au films deposited by ultrasonic spray pyrolysis

Polycrystalline ZnS semiconducting films have been prepared by ultrasonic spray pyrolysis technique in the form of planar and sandwich configurations using amorphous and ZnO coated glass substrates. Deposition of ZnS films by the spray pyrolysis has been studied extensively by several investigators and the process parameters have been optimized to obtain films with good characteristics. However we report for the first time the preparation of ZnS films sandwiched between top and bottom electrodes on the transparent conducting ZnO films that have been produced by the spray pyrolysis technique. The produced ZnS films have been crystallized in a wurtzite structure. The electrical properties of the samples having planar and sandwich structures have been measured in dark at room temperature by applying the voltage values between 0.01 and 100 V.