Chemical Bath Deposition Process Research Articles

Electrosprayed MnO2 on ZnO nanorods with atomic layer deposited TiO2 layer for photoelectrocatalytic water splitting

We have designed and produced a hierarchical photocatalyst for water splitting by first fabricating ZnO nanorods via a chemical bath deposition (CBD) process using ZnO seeds electrosprayed onto In-doped tin oxide (ITO), then electrospraying MnO2 particles as a co-catalyst, and finally depositing an ultrathin passivation layer of TiO2 via atomic layer deposition. These hierarchical photocatalysts exhibit excellent photoelectrochemical properties and reduced photocorrosion compared to materials without TiO2 coating. Moreover, the MnO2-garnished ZnO nanorods obtained at 550 °C deliver a 1.7-fold enhancement in photocurrent density (0.95 mA/cm2) at 1.2 VAg/AgCl in 0.5-M Na2SO3 solution compared to ZnO nanorods without MnO2. We attribute improved photocurrent density to rapid charge transfer and charge separation at the ZnO–MnO2 interface. This investigation illustrates a balanced design of a nanoarchitecture for photoelectrodes that favors formation of effective photoelectrocatalytic sites while improving stability for potential large-scale water splitting applications.

Comparative studies of CdS thin films by chemical bath deposition techniques as a buffer layer for solar cell applications

Cadmium sulfide (CdS) buffer layer that decouples the absorber layer and window layer in thin-film solar cells was synthesized by two different chemical bath deposition (CBD) techniques with varying deposition parameters. X-ray diffraction (XRD) revealed that the CdS thin film crystallizes in a stable hexagonal wurtzite structure having a preferential orientation along (002) reflection plane with a crystallite size varying from 20 to 40 nm. First longitudinal optical phonon mode was identified at Raman shift of 305 cm−1. Uniform, granular, continuous, and smooth surface with an average grain sizes (< 100 nm) as well as small roughness (< 9 nm) was observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The symmetric composition of cadmium and sulfur along with larger grains (20 nm) was observed at higher deposition temperatures and times. The optical band gap of CdS samples obtained from process one was in the range of 2.3–2.35 eV, while the band gap by the second CBD process lay in between 2.49 and 2.65 eV, showing the most stable compound of CdS. The presence of a green emission band in photoluminescence spectra (PL) demonstrated that the CdS material has better crystallinity with minimum defect density. Hall effect studies revealed the n-type conductivity of CdS thin films with a carrier concentration values in the order of 1016 cm−3. Furthermore, CdS thin films fabricated by CBD process exposed better quality that might be more suitable material as a buffer layer for thin-film solar cells.

Three‐Dimensional GeSe Microstructured Air Brick Photocathode for Advanced Solar Water Splitting

Air brick‐structured GeSe is first synthesized by a rapid box thermal deposition method, and the GeSe thin film with such air brick novel structure demonstrates advanced photoelectrochemical (PEC) performance. It is found that the electrode position of a few CdS nanoparticles (NPs) on a GeSe microair brick (MAB) prior to the chemical bath deposition (CBD) of CdS buffer affects the coverage/passivation efficiency of CdS onto GeSe MAB. In this case, the electrodeposited CdS particles were likely to be the seed for CdS growth/adsorption of Cd2+ during the subsequent CBD process and also could serve as active sites between the adsorbed layer and buffer layer for collecting electrons and facilitating their transfer, ultimately reducing the recombination loss. The PEC performance, especially the current density, is obviously improved (8 mA cm−2 at 0 VRHE) compared with that of a device without CdS NPs (3.6 mA cm−2 at 0 VRHE). Moreover, surface modification with an 80 nm atomic layer deposition TiO2 protective layer not only slows the photocorrosion of the CdS layer to 5 h but also promotes the half‐cell solar‐to‐hydrogen efficiency to 1.47%. More than 180 μmol H2 and 90 μmol O2 are evolved during 3 h of sustained solar light illumination with the final Pt–TiO2/CdS/CdS‐NP/GeSe MAB device.

Improved photoelectrode performance of chemical solution-derived Bi2O3 crystals via manipulation of crystal characterization.

Three-dimensional Bi2O3 crystals with various morphologies were successfully synthesized on F-doped tin oxide substrates with and without homoseed layers via chemical bath deposition (CBD) routes. The structural analysis reveals that control of the pH value of the reaction solution resulted in as-grown Bi2O3 crystals with nanosheet and plate morphologies. A lower pH value of the reaction solution engendered formation of a porous sheet-like morphology of Bi2O3; by contrast, a higher pH value of the reaction solution is favorable for formation of solid Bi2O3 plates on the substrates. Furthermore, a sputter coated Bi2O3 seed layer with dual α- and β-Bi2O3 phases plays an important role in the CBD-derived Bi2O3 crystallographic structures. The Bi2O3 crystals formed via CBD processes without a sputter coated Bi2O3 homoseed layer demonstrated a high purity in β-Bi2O3 phase; those grown with a homoseed layer exhibited a dual α/β phase. The photoactive performance results show that construction of an α/β-Bi2O3 homojunction in the CBD-derived Bi2O3 crystals substantially improved their photoactive performance. Comparatively, the porous Bi2O3 nanosheets with a dual α/β-Bi2O3 phase demonstrated the highest photoactive performance among various Bi2O3 crystals in this study. The superior photoactivity of the porous α/β-Bi2O3 nanosheets herein is attributed to their high light absorption capacity and photoinduced charge separation efficiency. The experimental results in this study provide a promising approach to design CBD-derived Bi2O3 crystals with desirable photoelectric conversion functions via facile morphology control and seed layer crystal engineering.

Temperature Effect of Chemical Bath Deposition (CBD) to Fabrication and Characterization of Zinc Oxide Nanorods Thin Films Based Gas Sensing: Ethanol

Fabrication of zinc oxide (ZnO) nanorods thin films based gas sensing ethanol have been done. Ethanol belongs to volatile organic compound (VOC) that are dangerous if inhaled by humans in high concentrations, so that its detection is necessary. Temperature as kinetic controller of chemical bath deposition (CBD) process take effect to ZnO fabrication and characterization. ZnO nanorods thin films was synthesized onto glass substrate by dip-coating technique. ZnO nanorods was grown using Zn(NO3)2.4H2O and HMTA with ratio 1:1 under CBD condition at temperature 75°C, 83°C, and 87°C. Result of SEM showing ZnO CBD 83°C has nanorods shape with diameter size is 95.56 nm, furthermore at 75°C the formation of the nanorods was not completed yet while at nanorods became deconstructed. XRD result showed all of ZnO sample have hexagonal wurzite which are match well with ICDS-094004 card. Ethanol gas sensing tested at 100°C, 150°C, 200°C showed high sensitivity of the sensor up to 77.31% for ZnO CBD 75°C at 100°C. ZnO CDB 83°C sample at test 200°C have highest response on 2.22 min (tres) and 0.45 min (trec). Time respond and recovery will increase along with increasing of test temperature.

Antibacterial activity of ZnO nanoflowers deposited on biodegradable acrylic acid hydrogel by chemical bath deposition

In the first part of this study, acrylic acid (AA) hydrogels were produced by a free radical reaction. Chemical and morphological structures of AA-hydrogels were specified by using Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) techniques. In the second part of the study, ZnO nanoflowers were synthesized on the AA-hydrogel by using a chemical bath deposition (CBD) technique for the first time in the literature. The AA-hydrogel acted as the substrate in the CBD process. The deposition time effect on the morphological properties of ZnO nanoflowers was determined by applying SEM. According to the SEM results, the deposition time in the production of ZnO nanoflowers has played a vital role in the surface morphology. Chemical, morphological and thermal properties of the ZnO nanoflowers were determined by applying FT-IR, scanning electron microscopy-energy dispersive X-ray spectroscopy and thermogravimetric analysis techniques. Elemental mapping of ZnO nanostructures was carried out using SEM. The antibacterial activity of the ZnO nanoflower-deposited AA-hydrogel was determined against Gram-negative and Gram-positive bacteria. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were used as test microorganisms. Gram-negative bacteria were more resistant to hydrogels and ZnO nanoflowers compared to Gram-positive bacteria.

Cu-doped CdS thin films by chemical bath deposition and ion exchange

This work presents the synthesis and characterization of nanostructured cadmium sulfide thin films obtained by an ammonia-free chemical bath deposition process. Different levels of Cu ion doping were achieved by the ion exchange method of CdS at room temperature. The main objective was to control the energy band gap adjusting the copper concentration and to gather information about Cu-doped CdS thin films. Optical absorbance measurements were performed to obtain the band gap value through Tauc’s plot method. XPS measurements were used to obtain the copper and cadmium concentration. In addition, SEM micrographs were collected to obtain information about surface and structural arrangement on Cu-doped CdS thin films. It was also found that the exchange of cadmium by Cu-ions promoted the formation of a hexagonal crystalline structure, which was different than the initial pure cubic structure. Through optical characterization, it is possible to evaluate the impact of the metallic dopant on the band gap value, finding that it can be controlled by the percentage of added copper, which opens the possibility of applying this material to the development of electronic devices such as field effect transistors. In addition, a prototype of a MOS structure was fabricated employing both the undoped and the Cu-doped CdS thin film to corroborate its possible application as a field effect transistor.

Grafting Methyl Groups on the Si(111) Surface as a Buffer Layer for van der Waals Epitaxial Growth of ZnO Nanorods in Chemical Bath Deposition

The absence of an epitaxial relation of material growth with silicon substrates usually results from the formation of native oxide on the substrate surface, especially in the lengthy solution process at elevated temperature. An effective method to impede surface oxidation and the consequent inheritance of the lattice structure of the substrate are beneficial for the epitaxial growth. In this study, we use the two-step halogenation/methylation process to create a methylated Si(111) surface for the growth of ZnO nanorods in a chemical bath deposition (CBD) process. The grafted methyl groups effectively passivate the Si(111) surface, and the deposited ZnO nanorods exhibit an epitaxial relation with the silicon substrate—ZnO[0001]//Si[111]; ZnO{11̅00}//Si{22̅0}. Because no chemical bonding is formed between the ZnO nanorods and the Si(111) substrate, this solution process exhibits the characteristics of the van der Waals epitaxial (vdWE) growth. The approach developed in this study paves a way for vdWE growth of nanostructures on Si substrates by the CBD process.

A rational design of CdS/ZnFe2O4/Cu2O core-shell nanorod array photoanode with stair-like type-II band alignment for highly efficient bias-free visible-light-driven H2 generation

In this study, a novel photoanode of ternary CdS/ZnFe2O4/Cu2O core/shell heterojunction nanorod arrays (NRAs) was fabricated via combining two-step hydrothermal method with a facile chemical bath deposition process. Under bias-free visible light irritation, the photocurrent density of the CdS/ZnFe2O4/Cu2O core/shell nanorod array (NRA) photoanode is 3.3 mA cm−2, 2.2 and 3.3-fold as high as that of CdS/ZnFe2O4 and CdS NRAs, respectively. In addition, an average H2 generation rate of the CdS/ZnFe2O4/Cu2O core/shell NRA photoanode is as high as 134 μmol h-1, 2.2-fold of CdS/ZnFe2O4 and 4.5-fold of CdS NRA photoanodes. Furthermore, the CdS/ZnFe2O4/Cu2O core/shell NRA photoanode shows a good photostability and achieves a photocurrent density of over 3 mA cm−2 during continuous light irradiation of 2 h. Significant enhancement for H2 evaluation of the CdS/ZnFe2O4/Cu2O core/shell NRA photoanode is ascribed to the efficient charge transfer and separation, which is achieved by its novel band alignment of stair-like type-II structure.

Current Spreading Length and Injection Efficiency in ZnO/GaN-Based Light-Emitting Diodes

We report on carrier injection features in light-emitting diodes (LEDs) based on nonintentionally doped-ZnO/p-GaN heterostructures. These LEDs consist of a ZnO layer grown by chemical-bath deposition (CBD) onto a p-GaN template without using any seed layer. The ZnO layer (~1- $\mu \text{m}$ thickness) consists of a dense collection of partially coalesced ZnO nanorods, organized in wurtzite phase with marked vertical orientation, whose density depends on the concentration of the solution during the CBD process. Due to the limited conductivity of the p-GaN layer, the recombination in the n-region is strongly dependent on the spreading length of the holes, ${L}_{h}$ , coming from the p-contact. Moreover, the evaluation of ${L}_{h}$ is not easy and generally requires the design and the fabrication of several LED test patterns. We propose a simple and effective method to calculate ${L}_{h}$ , just based on simple considerations on ${I}$ – ${V}$ characteristics, and a way to improve the injection efficiency in the n region based on a noncircular electrode geometry. In particular, an interdigitated electrode structure is proved to be more efficient in terms of hole injection from n- to p-region.

Growth and Photocatalytic Properties of Gallium Oxide Films Using Chemical Bath Deposition

Gallium oxide (Ga2O3) thin films were fabricated on glass substrates using a combination of chemical bath deposition and post-annealing process. From the field-emission scanning electron microscopy and x-ray diffraction results, the GaOOH nanorods precursors with better crystallinity can be achieved under higher concentrations (≥0.05 M) of gallium nitrate (Ga(NO3)3). It was found that the GaOOH synthesized from lower Ga(NO3)3 concentration did not transform into α-Ga2O3 among the annealing temperatures used (400–600 °C). Under higher Ga(NO3)3 concentrations (≥0.05 M) with higher annealing temperatures (≥500 °C), the GaOOH can be transformed into the Ga2O3 film successfully. An α-Ga2O3 sample synthesized in a mixed solution of 0.075 M Ga(NO3)3 and 0.5 M hexamethylenetetramine exhibited optimum crystallinity after annealing at 500 °C, where the α-Ga2O3 nanostructure film showed the highest aspect ratio of 5.23. As a result, the photodegeneration efficiencies of the α-Ga2O3 film for the methylene blue aqueous solution can reach 90%.

Optical investigations on PVA capped SnS nanocrystalline films deposited by CBD process

Tin monosulphide (SnS) nanocrystalline films, capped by polyvinyl alcohol (PVA) were successfully deposited on glass substrates using chemical bath deposition (CBD). The films were deposited at different deposition times that vary in the range, 45–90 min The XRD spectra indicated that PVA capped SnS layers were polycrystalline in nature and exhibiting orthorhombic structure. The average crystallite size was evaluated using W-H plots. Cross section view of SEM micrographs were used to determine the thickness of the films. The optical behaviour of all the deposited layers was investigated in relation to deposition time. The studies revealed a very high optical absorption coefficient of ∼105 cm−1 for all the deposited layers and the optical band gap varied from 1.79 eV to 1.55 eV with increase of deposition time. The band gap values obtained were higher than the bulk value of 1.3 eV, which is attributed to quantum confinement effect. The size of particles, calculated using Brus equation, varied marginally in the range, 5.8–8.4 nm with increase of growth time. The optical parameters such as refractive index, extinction coefficient, high frequency dielectric constant, optical carrier concentration, relaxation time and optical conductivity were also determined.

UV-illuminated chemical bath deposition of CdS buffer layer for CIGSSe solar cells

In this paper, we compare the performance of Cu(In,Ga)(S,Se)2 (CIGSSe) thin film solar cells with a CdS buffer layer grown by chemical bath deposition (CBD) with UV irradiation of 365 nm or 254 nm at an output power of 8 W. The effects of UV light irradiation on the CBD-CdS thin film deposition mechanism were investigated through chemical and electro-optical studies. UV light irradiation during the solution process promotes the hydrolysis of thiourea, thereby inhibiting the formation of the intermediate products being developed on the reaction pathways and decreasing the solution pH. Therefore, the efficiency of the CdS/CIGSSe solar cells was improved because of the increased elemental ratio of S/(S + O) in the CdS thin film. This very simple and effective approach can be used to control the S/O ratio of the CdS thin film fabricated by the CBD process without artificially controlling the process temperature, solution pH or concentration.

Designing WO3/CdIn2S4 type-II heterojunction with both efficient light absorption and charge separation for enhanced photoelectrochemical water splitting

WO3 is a typical photoanode material for photoelectrochemical (PEC) water splitting. However, the PEC activity of WO3 photoanode is limited by its poor visible light absorption as well as severe carrier recombination at the electrode/electrolyte interface. Herein, we integrate small-band-gap CdIn2S4 nanoplates with hydrothermally grown WO3 nanowall arrays to form into a three-dimensional (3D) WO3/CdIn2S4 heterojunction through a chemical bath deposition process. The synthesis parameters of CdIn2S4, including reaction time and temperature, have been tuned to optimize the PEC performance. The WO3/CdIn2S4 composite photoanode prepared at 50 °C for 5 h exhibits the highest photocurrent of 1.06 mA cm−2 at 1.23 V versus reversible hydrogen electrode without the presence of holes scavenger, which is about 5.9 times higher than that of bare WO3 photoanode. The band alignment between WO3 and CdIn2S4 is confirmed by the ultraviolet–visible light absorption spectra and ultraviolet photoelectron spectra. The PEC performance enhancement is attributed to the enhanced light absorption benefiting from the small band gap of CdIn2S4 and efficient charge separation originating from the type-II alignment between WO3 and CdIn2S4.

Construction of spherical NiO@MnO2 with core-shell structure obtained by depositing MnO2 nanoparticles on NiO nanosheets for high-performance supercapacitor

The 3D spherical NiO@MnO2 composites grown on Ni foam with core-shell structure were prepared by a hydrothermal process followed by a chemical bath deposition process, and then the mechanism improving the electrochemical performance of NiO by MnO2 modification were investigated by the first-principles calculations for the first time. This core-shell structure promotes an efficient contact between electrolyte and active materials, and the distinct architecture can offer fast transfer channels of ion and electrons. The initial capacitances of NiO, NiO@MnO2 (deposition time of MnO2 is 20 min), NiO@MnO2 (deposition time of MnO2 is 30 min) and NiO@MnO2 (deposition time of MnO2 is 60 min) at 10 A g−1 are 931.6, 1064.4, 1227.2 and 766.8 F g−1, respectively. After 10000 cycles, the reversible capacitances attenuate to 352.8, 661.0, 1089.4 and 616.6 F g−1, respectively. NiO@MnO2 (deposition time of MnO2 is 30 min) shows the most excellent reversible capacitance at each cycle and the highest retention rates after 10000 cycles among all samples. The first-principles calculation confirms that a strong interfacial interaction between NiO and MnO2 can be generated, and then the atomic relaxations at the interface are rather small due to the well-matched interface and epitaxial bonding, resulting in a relatively small interfacial polarization of NiO@MnO2 composites during cycling. The outstanding rate capability and cycle performance of NiO@MnO2 (deposition time of MnO2 is 30 min) electrode are attributed to the synergistic effect and particular 3 D architectures.

Novel Ni foam based nickel oxalate derived porous NiO nanostructures as highly efficient electrodes for the electrooxidation of methanol/ethanol and urea

In this paper, porous NiO with three-dimensional (3D) nanostructures are prepared by a chemical bath deposition (CBD) process in oxalic acid solution at a fixed temperature using Ni foam (NF) as the substrate and Ni source, and followed by an electrochemical activation treatment in an alkaline medium. The special 3D porous structure of the as-prepared NF based NiO (NiO/NF) electrode is benefit for the diffusion of fuels (CH3OH/C2H5OH and urea) during the electrochemical reaction. Besides, the obtained NiO may combine with the remained nickel oxalate (NiC2O4) to further enhance the catalytic performance due to its synergistic effect. At 0.60 V, the electrooxidation current density reached 257 mA cm−2 in 1.0 mol dm−3 NaOH and 0.40 mol dm−3 CH3OH, and a high performance of 120 mA cm−2 was achieved in 1.0 mol dm−3 NaOH and 0.10 mol dm−3 C2H5OH. The oxidation current density reached 222 mA cm−2 in 0.1 mol dm−3 urea with the NaOH concentration of 8.0 mol dm−3 at around 0.48 V. The facile preparation method, high electrocatalytic activity, low cost and various applications make the NiO/NF be a promising electrode material.

Fabrication of 4.9% efficient Cu2ZnSnS4 solar cell using electron-beam evaporated CdS buffer layer

The chemical bath deposition process of depositing CdS buffer layer was replaced with electron-beam evaporation method, full vacuum preparation process, which is more environmentally friendly and non-solution contact, was achieved to prepare Cu2ZnSnS4 (CZTS) solar cells. First, the influence of growth rate on the structural, optical, morphological, electrical properties of electron-beam evaporated CdS films was investigated. CdS thin films were deposited at growth rates of about 3, 6, 9, 12 Å/s, respectively. The results revealed that CdS thin films deposited at lower rate showed better crystallinity, higher transmittance, lower carrier concentrations, preferred for the application in CZTS solar cells. Then, kesterite Cu2ZnSnS4 thin film solar cells using the optimal CdS thin films as a buffer layer are fabricated, and a best efficiency of 4.87% was demonstrated. The statistical distribution of device performance parameters of 150 solar cells using electron-beam evaporated CdS buffer layer was also demonstrated.

Optical properties of ZnO nanorods derived from chemical bath deposition process with different seeds solution concentration

Owing to their high surface to volume ratio and fast electron transfer, zinc oxide (ZnO) nanorods have been well-known as potential nanostructured material for various applications including sensors, dye sensitized solar cells, optoelectronic, transparent heater and biomedical devices. Among other synthesizing techniques for obtaining ZnO nanorods, chemical bath deposition (CBD) has been thought as a simple and low-cost method. However, there are several processing parameters that need to be investigated for the above-mentioned applications where the highly optical transparency of thin film ZnO nanorods grown on glass substrates is one of important targets to be achieved. In this work, ZnO nanorods were synthesized through CBD process at low temperature (0°C) by using seed solution prepared by dissolving 1: 1 equimolar zinc nitrate tetrahydrate and hexamethylene tetraamine. For investigation purposes, three different concentration of seed solutions i.e. 0.005, 0.025 and 0.05 M were used. Thin films containing ZnO nanoseeds were formed by spin coating the precursors on the glass substrates, followed with annealing at 2000C for 5 minutes. Finally, the ZnO nanorods were further grown at 90ºC for 3 hours in the beaker glass using the same solution. Xray diffraction (XRD) analysis showed that all ZnO nanorods demonstrated a strong (002) peak belong to wurtzite phase. It was found that the estimated crystallite size and band gap energy (Eg) for ZnO nanorods derived from the seed solutions of 0.005, 0.025 and 0.05 M were 21.42, 137.11, 171.39 nm, and 3.60, 3.20, 3.18 eV, respectively. However, the optical transparency was adversely lowered from about 75 to 40 % as a result of increased coverage of ZnO nanorods on the glass substrate. For transparent heater application where, a desired combination of high optical transparency and suitable electronic properties is needed, the current results were considered to be promising.

Effective two-step chemical deposition for homogeneous lead sulfide thin films on a flexible polymer substrate

Chalcogenide PbS has been extensively studied as a p-type semiconductor material for various optoelectronic devices. Here, an effective two-step chemical bath deposition process is introduced to achieve dense microstructure of PbS thin films specifically for a flexible polyethylene terephthalate (PET) substrate. Three different types of substrates, such as Cu foils, glass substrate and PET, were initially examined to compare different crystal growth behaviors of PbS thin films depending on the choice of substrate. Only the PET substrate demonstrated an unacceptable coverage of films even with the extended deposition due to a retarded growth presumably with more scattered initial distribution of nuclei. Conclusively, two-step deposition processing at a low temperature of 40 °C for the PET substrate was successful in achieving homogeneous microstructures with proper bandgap and film thickness. As a promising result, the 60 min plus 60 min-double depositions at 40 °C produced an ideal bandgap of ~1.58 eV with a proper film thickness of ~200 nm.

Generation of oxygen interstitials with excess in situ Ga doping in chemical bath deposition process for the growth of p-type ZnO nanowires

The current work focuses on the incorporation of excess amount of gallium (Ga) in zinc oxide (ZnO) nanowires to generate oxygen interstitials for developing p-type conductivity. Ga has been used as an n-type dopant in ZnO lattice by reducing its inherent vacancies up to 3% molar ratio of Ga and Zn employing chemical bath deposition technique. However, the addition of more than 4% of gallium nitrate in the bath solution creates oxygen interstitials which are confirmed from the presence of X-ray photoelectron spectroscopy (XPS) peak at 532.6 eV and the relevant cathodoluminescence (CL) peak at 626 nm of the grown Ga-doped ZnO nanowires. The p-type conductivity of such ZnO nanowires has been confirmed from current–voltage, capacitance–voltage and Hall voltage measurements. The reproducibility of the results indicates the incorporation of excess Ga to be a promising technique for growing p-type ZnO nanowires.