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As compared to other deposition techniques such as atomic layer deposition, chemical vapour deposition and sputtering, aerosol deposition (AD) is a simple and cost-effective technique to produce ZnO thin films. In this work, the effect of deposition cycles on the structural, optical, and photo-conversion efficiency (PCE) of dye sensitized solar cells of ZnO thin films deposited by AD (AZ) was systematically studied. The structural, optical, and PCE% of two-cycle deposited ZnO thin film (AZ-II) exhibited the highest performance. Further increment in deposition cycle caused deterioration in the structural, optical, and PCE performance. The thickness of ZnO thin films decreased due to abrasion of the deposited film by the subsequent stream of highly energetic ZnO particles. Loosely bound particles could be found on the surface of ZnO thin film after three deposition cycles (AZ-III). The AZ-III films exhibited poor crystal quality, with many crystal defects such as interstitial oxygen as suggested in room temperature photoluminescence analysis. [ABSTRACT FROM AUTHOR]

Aerosol deposition (AD) is a simple, dry raw-powder deposition process in which the targeted film is formed by direct bombardment of accelerated starting powder onto the substrate surface at room temperature. Despite the increased interest in AD film formation, no work has been completed to systematically investigate the formation of dense zinc oxide (ZnO) films using the AD method and their optical properties. Therefore, this study was carried out to investigate the effect of AD gas flow rate on the formation of AD films and the optical properties of aerosol-deposited ZnO films. ZnO films with nanosized (<40 nm) crystallites were successfully deposited on FTO substrates at room temperature. A dense and uniform layer of aerosol-deposited ZnO films with a roughened surface was obtained without subsequent heat treatment. With the increase in the AD gas flow rate, the crystal size and the AD film's thickness were reduced. The Raman spectroscopy verified that the thin film was of a ZnO wurtzite structure. The room temperature photoluminescence of the ZnO thin film produced strong visible emissions. The findings of this work demonstrated that AD can be an alternative technique for the rapid deposition of dense and thick ZnO films for optoelectronic applications. [ABSTRACT FROM AUTHOR]

The morphological evolution of the zinc oxide (ZnO) nanostructures generated by hot-water treatment (HWT) of sol–gel derived coatings as a function of temperature from 30 to 90 °C was investigated. With increasing HWT temperature, the ZnO crystals evolved from nanoparticles to rod-like and needle-like nanostructures. High-resolution transmission electron microscope observations of rod-like and needle-like nanostructures generated at 60 and 90 °C indicated single crystal ZnO wurtzite structure was obtained. All the hot-water treated samples exhibited blue emission at approximately 440 nm in room temperature. The intensity of blue emission increased with higher HWT temperatures. The unique photoluminescence emission characteristic remained even after heat-treatment at 400 °C for 1 h. As the emission peak obtained in our work is approximately 440 nm (2.82 eV), the emission peak is corresponding to the electron transition from the interstitial Zn to the top of valence band. This facile formation of blue-emitting ZnO nanostructures at low-temperature can be utilized on substrate with low thermal stability for optoelectronic applications such as light emitting devices and biological fluorescence labeling. [ABSTRACT FROM AUTHOR]

ZnO composite films consisting of ZnO nanorods and nanosheets were prepared by low-temperature hydrothermal processing at 80°C on seeded glass substrates. The seed layer was coated on glass substrates by sol–gel dip-coating and pre-heated at 300°C for 10min prior to hydrothermal growth. The size of the grain formed after pre-heat treatment was ~40nm. A preferred orientation seed layer at the c-axis was obtained, which promoted vertical growth of the ZnO nanorod arrays and formation of the ZnO nanosheets. X-ray diffraction patterns and high-resolution transmission electron microscope (HR-TEM) images confirmed that the ZnO nanorods and nanosheets consist of single crystalline and polycrystalline structures, respectively. Room temperature photoluminescence spectra of the ZnO nanorod–nanosheet composite films exhibited band-edge ultraviolet (UV) and visible emission (blue and green) indicating the formation of ZnO crystals with good crystallinity and are supported by Raman scattering results. The formation of one-dimensional (1D) ZnO nanorod arrays and two-dimensional (2D) ZnO nanosheet films using seeded substrates in a single low-temperature hydrothermal step would be beneficial for realization of device applications that utilize substrates with limited temperature stability. The ZnO nanorods and nanosheets composite structure demonstrated higher photocatalytic activity during degradation of aqueous methylene blue under visible-light irradiation. [ABSTRACT FROM AUTHOR]

SUMMARY Well-aligned zinc oxide (ZnO) nanorod arrays were formed on indium tin oxide (ITO)/glass substrates via a low-temperature hydrothermal growth of a sol-gel-derived seed layer. The seed layer was heat treated at 300 °C for 10 min prior to the hydrothermal growth using optimized conditions from our previous work to form well-aligned ZnO nanorod arrays. Hydrothermal growth time was varied for 4, 8, 12 and 24 h. Flat-top hexagonal ZnO nanorod arrays were obtained, and the length of the ZnO nanorods formed increased from approximately 150 nm after 4 h to approximately 2 µm after 24 h using a single reactive bath. X-ray diffraction patterns showed predominant ZnO peak at (002) plane for all the samples. Photoluminescence spectra of the ZnO nanorod arrays showed peaks at ultra-violet and green region, which indicated good crystalline crystal formation containing oxygen-related defects. Raman scattering results obtained showed strong band at 438 cm−1 that correlated to E2 non-polar hexagonal wurtzite phase. Dye-sensitized solar cells (DSSC) based on the well-aligned ZnO nanorod arrays were fabricated. The maximum conversion efficiency of 0.22% was achieved for the nanorods formed after a prolonged hydrothermal time of 24 h. The conversion efficiency of the DSSC increased with hydrothermal exposure time as longer ZnO nanorods provided larger surface for dye adsorption to generate more electrons. Improved crystallinity of the ZnO nanorods provided at prolonged hydrothermal time also contributed to the higher conversion efficiency as the electron transportation was enhanced. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The effect of an external direct current (DC) electric field induction during hot-water treatment (HWT) on sol3gel derived ZnO coatings for controlled formation of good crystalline ZnO films was investigated. The electric field induced hot-water treatment (EF-HWT) was found to influence the formation of crystalline ZnO nanostructures on the ZnO gel films at low-temperature of 50°C for 3h. The effects of time, voltage and substrates used during the EF-HWT were investigated. Flower-like precipitates of hexagonal zinc oxide were generated from the zinc acetate derived ZnO gel film on a silicon single crystal substrate at the negative electrode by applying an electric field. Significant c-axis orientation of hexagonal ZnO on the silicon substrate was confirmed from XRD patterns. These results demonstrated that the EF-HWT of sol3gel derived ZnO films is a promising, low-temperature technique to control the morphology and crystallinity of oxide coatings. [Copyright &y& Elsevier]

Abstract: Rod-like undoped and Ce-doped ZnO nanostructures have been formed using hot-water treatment of the undoped and Ce-doped sol–gel derived layer at low temperature of 60°C for 30min on glass substrates. The concentration of Ce doping was varied from 2 to 20at% in the precursor films. Morphological structures and optical properties of the hot-water treated ZnO films were investigated and compared with those of the conventional, annealed ZnO films. The resultant undoped and Ce-doped rod-like ZnO films showed ultraviolet (UV) and strong blue emissions. The photoluminescence of the Ce-doped films exhibited blue shift in UV emission and reduced blue emission intensity, compared to pure ZnO due to the incorporation of Ce. Increment of broad green emission intensity is observed with increased Ce doping in the precursor concentration for the hot-water treated films, which indicates the formation in Ce vacancies. Ce-doped ZnO films obtained which show promising optical properties can be used for the fabrication of optoelectronics devices utilizing substrates with low thermal stability such as organic polymers. [Copyright &y& Elsevier]

Abstract: The effects of surface oxidation of etched metallic Zn foils by hot-water treatment at 90°C for 4, 8, 12 and 24h were investigated. ZnO nanostructures consisting of nanowires and nanorods were obtained at different hot-water treatment times. The photoluminescence spectra of the as-formed ZnO nanostructures exhibit near band edge UV emission, indicating their good crystallinity. Further evidence of good crystallinity is the HR-TEM observations of the lattice fringes of wurtzite ZnO. Raman scattering of the ZnO nanostructures indicates that crystallinity is improved, and the number of oxygen vacancies is reduced at longer durations of hot-water treatment. [Copyright &y& Elsevier]

• Zinc oxide/reduce graphene oxide (RGO) were used as working electrodes. • The efficiency of dye sensitized solar cell deteriorated with addition of RGO. • RGO acted as recombination centres and hindered charge carriers' transportation. Dye-sensitized solar cell (DSSC) is a low-cost and thin film based solar cell. Many research works reported that the use of reduced graphene oxide (RGO) could improve the performance of DSSCs. However, this might not necessarily correct as it depends on the thin film preparation technique. In the present work, the effect of RGO on the power conversion efficiency (PCE) of zinc oxide (ZnO) thin film based DSSCs was studied. The ZnO/RGO nanocomposite films with different volume of RGO suspension, i.e., 1, 2, 3 and 4 ml of RGO suspension was mixed with the ZnO paste. The mixture was deposited on the fluorine doped-tin oxide (FTO) conductive substrates by paste coating method. These ZnO/RGO film/FTO substrates were used as working electrodes in DSSCs. The cell's efficiency of ZnO with 0, 1, 2, 3, and 4 ml of RGO contents reached 2.71, 2.61, 2.07, 1.72 and 1.71 %, respectively. The PCE of ZnO/RGO film decreased with increasing amount of RGO solution. Although RGO is known for its good conductivity, adding of RGO could deteriorate the charges transportation in DSSCs. [ABSTRACT FROM AUTHOR]

ZnO nanopagoda arrays (NPGs) modified with Ag and Ag 2 S nanoparticles (NPs) were fabricated using aqueous downward growth and SILAR techniques and investigated as photoanodes for the photoelectrochemical system. The crystal structure, morphology, elemental composition, optical characteristics, and photoelectrochemical performance of the fabricated samples were studied. The obtained results disclosed that the successful deposition of Ag and Ag 2 S NPs on ZnO NPGs' surface not only enhanced the visible light-harvesting but also promoted the e−/h+ separation and injection. In addition, various SILAR cycles were investigated. The optimum eight SILAR cycles for Ag–Ag 2 S NPs deposition on ZnO NPGs achieved the maximum photocurrent of 2.91 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE), about five folds superior to that of bare ZnO NPGs. It also demonstrated the improved applied bias photon-to-current conversion efficiency of 0.43% at 0.6 V vs. RHE. The charge transfer and PEC mechanisms for the fabricated ZnO NPGs/Ag–Ag 2 S NPs photoanodes were also proposed. This study offers a facile fabrication of a distinctive ZnO NPGs morphology and an improvement of the PEC performance through the synergistic effect of the LSPR effect of Ag NPs and visible light sensitization of Ag 2 S NPs. [Display omitted] • ZnO NPGs was synthesized using an aqueous chemical downward procedure. • Various SILAR cycles of Ag–Ag 2 S NPs were deposited over ZnO NPGs surface. • The eight cycles of Ag–Ag 2 S NPs over ZnO NPGs showed the best PEC performance. [ABSTRACT FROM AUTHOR]