Length Of ZnO Nanorods Research Articles

Improving the Efficiency of Dye-Sensitized Solar Cells by Growing Longer ZnO Nanorods on TiO2 Photoanodes

By increasing the temperature of hydrothermal reactions from 70 to 100°C, vertically aligned ZnO nanorods were grown on the TiO2 thin film in the photoanode of dye-sensitized solar cells (DSSCs) as the blocking layer to reduce the electron back recombinations at the TiO2/electrolyte interfaces. The length effects of ZnO nanorods on the photovoltaic performances of TiO2 based DSSCs were investigated by means of scanning electron microscope, X-ray diffractometer, photoluminescence spectrophotometer, and the photocurrent-voltage measurement. Under the illumination of 100 mW/cm2, the power conversion efficiency of DSSC with ZnO nanorods decorated TiO2 thin film as its photoanode can be increased nearly fourfold from 0.27% to 1.30% as the length of ZnO nanorods increases from 300 to 1600 nm. The enhanced efficiency of DSSC with ZnO nanorods decorated TiO2 thin film as the photoanode can be attributed to the larger surface area and the lower defect density in longer ZnO nanorods, which are in favor of more dye adsorption and more efficient transport in the photoanode.

Size-controllable growth of ZnO nanorods on Si substrate

Here we report a simple two-step chemical-solution-based method to grow highly oriented and size-controllable ZnO nanorods on ZnO-seeded Si substrate. The morphology of the grown ZnO nanorods was examined by field emission scanning electron microscopy. The structure was characterized by X-ray diffraction and Raman scattering spectrum. Photoluminescence spectra were measured at room temperature and low temperatures to evaluate the photoluminescence properties of the ZnO nanorods. The grown ZnO nanorods are structured with hexagonal wurtzite. The diameter and length of ZnO nanorods can be controlled by varying the crystal quality of the underlying ZnO seed layers. The crystal quality of the seed layers gets improved as the deposition time and annealing temperature for ZnO seed layers are increased. The effects of annealing on the ZnO nanorods were also studied.

Lead‐free mesoscopic Cs2SnI6 perovskite solar cells using different nanostructured ZnO nanorods as electron transport layers

Lead‐free and more air‐stable perovskite Cs2SnI6 absorber with a direct bandgap of 1.48 eV is synthesized via a modified solution process. Different nanostructured ZnO nanorod arrays as electron transport layers and hole blocking layers are grown by controlling the seed layer and used to fabricate mesoscopic perovskite solar cells with Cs2SnI6 as light absorber layer. The influences of ZnO seed layers and nanorod morphology on the device photovoltaic performance were also investigated. With careful control of ZnO nanorod length and pore size to ensure high loading of the Cs2SnI6 absorber, we achieved power conversion efficiency of near 1%. magnified image

Structural, optical and photocatalytic properties of ZnO nanorods: Effect of aging time and number of layers

ZnO thin films were prepared by sol–gel dip coating method onto glass substrates. The effects of aging time of the starting solution (2, 10 and 30 days) and the number of coats (2, 5 and 10 coatings) on structural, morphological and optical properties were investigated. Photocatalytic efficiency was also assessed. X-ray diffraction analysis indicates that all the films exhibit a Zincite-type structure with a preferred grains orientation along the [002] direction. The preferred orientation factor (POF) increases with aging time while the crystallite size decreases. The field emission scanning electron microscopy observations reveals nanorods morphology. The length of ZnO nanorods increase with increasing number of layers whereas their length decreases as a function of aging time while adopting a random orientation. A high optical transparency is observed for all ZnO thin films, ranging from 90 up to 96%. Methylene Blue (MB) dye photocatalytic degradation was found increases with aging time, reaching almost 94% after 10h under UV irradiation. The apparent reaction rate (Kapp) obtained by Langmuir-Hinshelwood model increases with increasing aging time from, from 0.218h−1 for 2 days to reach a steady state around 0.270h−1. Nevertheless, a small variation of Kapp was recorded when varying the number of coats; 0.223–0.226h−1.

Fabrication and Characterization of ZnO Nanorods on Multiple Substrates.

In this study, we present the fabrication and characterization of ZnO nanorods (NRs) grown on p-Si, gold (Au) and nickel (Ni) coated on Si wafer, indium tin oxide (ITO), and quartz substrates. The aqueous chemical growth method is used for the vertical growth of ZnO NRs on multiple substrates. The samples are characterized with scanning electron microscope and energy dispersive X-ray spectroscopy to probe into the growth, alignment, density, diameter, and length of ZnO NRs on multiple substrates. It is found that under same conditions, like growth temperature, growth time, and solution concentration, ZnO NRs on ITO and quartz have same length but comparatively larger diameter than on other samples. The effects of growth time on the diameter and length of ZnO NRs are also explored. All the samples are characterized with probe station to look at the current-voltage (I-V) behavior of ZnO NRs on multiple substrates. It is found that ZnO NRs on p-Si show a simple p-n heterojunction diode like behavior. ZnO NRs grown on Au- and Ni-coated Si wafers show Schottky I-V characteristic behaviors while ZnO NRs on ITO show a simple ohmic I-V response with comparatively higher level of current. Finally, the I-V response of ZnO NRs on p-Si is also studied under ultraviolet illumination. Because of the photo-generated carriers in ZnO, the sample shows higher level of current upon illumination.

Flower-like ZnO nanorod arrays grown on HF-etched Si (111): constraining relation between ZnO seed layer and Si (111)

We demonstrate the formation of self-assembled homogenous flower-like ZnO nanorods over a ZnO seed layer deposited on a HF-etched Si (111) substrate. The typical flower-like morphology of ZnO nanorod arrays is ascribed to the formation of the island-like seed layer which is deposited by the drop method followed by annealing at 300 °C. The island-like ZnO seed layer consists of larger ZnO grains, and is built by constraining of the Si (111) surface due to pattern matching. Pattern matching of Si with ZnO determines the shape and size of the seed layer and this controls the final morphology of ZnO nanorods to be either flower like or vertically aligned. The high quality of the island-like ZnO seed layer enhances the diameter and length of ZnO nanorods. Besides, while the amorphous layer formed during the annealing process would influence the strained ZnO grain, that subsequent amorphous layer will not block the constraining between the ZnO grain and the substrate.

Optimal length of ZnO nanorods for improving the light-extraction efficiency of blue InGaN light-emitting diodes.

Optimal length of ZnO nanorods (NRs) on blue InGaN light-emitting diodes (LEDs) was investigated to improve the light-extraction efficiency (LEE) of the LED. X-ray diffraction, photoluminescence spectroscopy, and micro-Raman spectroscopy were employed to determine the structural and optical properties of the ZnO NRs with length of 300 nm and 5 μm grown by a hydrothermal method. From the conventional light output power versus injection current (L-I) measurement, we found that the light output power of the LEDs with 300-nm- and 5-μm-long ZnO NRs was approximately 14.6% and 40.7% greater, respectively, than that of the LED without the ZnO NRs at an operating current of 20 mA. In addition, there were almost no changes to the electrical properties of the ZnO-NR-coated LEDs. The effect of the length of the ZnO NRs on the LEE of the LEDs was theoretically verified with three-dimensional finite-difference time-domain (FDTD) analysis. The FDTD images of the optical power and far-field radiation patterns of the LEDs showed that more photons were guided to the out of the LED by the longer ZnO NRs than by the shorter ZnO NRs grown on the LEDs.

Enhancing performance of inverted polymer solar cells using two-growth ZnO nanorods

In ordinary polymer solar cells, the short exciton diffusion length causes increasing probability of electron–hole recombination as the active layer thickness exceeds the diffusion length. Hence, the diffusion sets a thickness limitation of the active layer. ZnO nanorods have been used to provide an advantage of electronic path, making it possible to increase the effective thickness of the active layer. However general hydrothermal treatment has a limitation of the ZnO nanorod length because the nanorods accelerate their growth speed horizontally after growing over a period of time, leading to the reduction of space to be filled with the organic light absorber. Thus, in this work, two-growth ZnO nanorods are employed to overcome the above limitation. The first growth process is for defining nanorod density, while the second process is to increase the length without much expansion of the rod size. This allows for elastically tuning the morphology between the active layer and the ZnO electron transport layer to achieve deeper and superior infiltration of organic light absorber. Consequently, this improves the performance of the device. The power conversion efficiencies of devices in PBDTTT-C-T/PC71BM and PTB7/PC71BM are then enhanced from 5.40% to 7.80% and 7.24% to 8.01%, respectively.

Cu-implanted ZnO nanorods array film: An aqueous synthetic approach

Pure and Cu doped ZnO nanorods array are synthesized via two step chemical bath deposition method. The seed layer is prepared by successive ionic layer adsorption reaction (SILAR) method. The synthesized materials have been systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDAX), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectroscopy. SEM pictures show the existence of vertically well aligned hexagonal ZnO nanorods. EDAX spectrum confirms the presence of Cu in ZnO nanorods. High intense peak of (002) plane and E2high mode for XRD and Raman spectrum respectively, suggest the ZnO nanorods are adopted c-axis orientation perpendicular to substrate. XRD and Raman analysis shows the presence of tensile strain in Cu doped ZnO nanorods. Effect of Cu doping on lattice constants, unit cell volume and Zn–O bond length of ZnO nanorods have also been studied. Room temperature PL measurement exhibits two luminescence bands in the spectra i.e. UV emission centered at 3.215eV and a broad visible band. Theoretical investigation for capping action of triethanolamine is done by Hartree–Fock(HF) method with 3-21G basis set using Gaussian 09 program package.

Dye-Sensitized Solar Cells Composed of Well-Aligned ZnO Nanorod Array Grown with Chemical Bath Deposition Method as the Photo-Electrode

Well-aligned ZnO nanorod arrays were prepared at different deposition times to determine the correlation between the length of the photoelectrodes and the photovoltaic performance in dye-sensitized solar cells. The length of the ZnO photoelectrode was controlled to 1.2, 2.7 and 4.0 μm by the deposition time. The DSSCs composed of the longer ZnO nanorods showed much better photovoltaic performance due to the enhanced amount of dyes adsorbed and electron injection, as determined by the intrinsic photon-to-current efficiency and electrochemical impedance spectroscopy. The photon-to-current efficiency of the DSSC containing ZnO photoelectrode was considered with the aspect of the length of ZnO nanorods.

Controllable growth of oriented ZnO nanorods using Ga-doped seed layers and surface acoustic wave humidity sensor

ZnO nanorods were grown on a Si/AlN structure using hydrothermal method. The fabricated ZnO nanorod film was used as a sensitive material layer for surface acoustic wave (SAW) humidity sensor. The concentration of gallium, which was doped into ZnO seed layers prior to ZnO nanorod chemical growth, varied from 0wt% to 3wt% to control ZnO nanorod growth. The result shows that gallium dopant was crucial for controllable dimension of ZnO nanorods. ZnO nanorod length increased and ZnO nanorod diameter decreased when Ga concentration increased from 0wt% to 3wt%. The ZnO nanorods had a hexagonal wurtzite structure, and were aligned vertically on the substrate. SAW properties (e.g., resonance frequency) over relative humidity (RH) ranging from 10% to 90% at room temperature were investigated. The results show that the frequency shift of the SAW humidity sensors increased with increasing Ga dopant concentration. The largest shift in the frequency response was approximately 970kHz at 90% RH for sensors with ZnO nanorods grown on 3wt% Ga-doped ZnO seed layer. This result was caused by the highest surface-to-volume ratio of the ZnO nanorod sensing layer.

A facile and green strategy for large-scale synthesis of silica nanotubes using ZnO nanorods as templates

Hollow silica nanostructures exhibit important applications in catalysis, sensing, and gene delivery due to their increased surface areas, good biocompatibility, and unique optical features. Here we report a simple and green approach to synthesize silica nanotubes using environment—friendly ZnO nanorods as templates. The ZnO nanorods are first coated with a layer of uniform silica shell by a sol–gel method. Then silica nanotubes are derived from the ZnO@SiO2 nanohybrids after removal of the ZnO nanorod cores in diluted hydrochloric acid solution. The samples at different stages were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Energy-dispersive X-ray spectroscopy, and Transmission electron microscopy. By controlling the structure of the ZnO@SiO2 nanohybrids, such as shell thickness, and the diameter and length of ZnO nanorods, size controllable SiO2 nanotubes can be expected.

Effects of Growth Time on Morphologies of ZnO Nanorod Arrays

well-aligned ZnO nanorod arrays (ZNRAs) grown on the ZnO seed layers coated p-silicon (p-Si) substrates in various times from 1.5 to 5 hr have been fabricated from aqueous solutions at low temperature. Morphologies, crystalline structure and optical transmission were investigated by a scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The results showed that ZNRAs grew vertically from the substrates, having uniform thickness and length distribution, the average diameters and length of ZnO nanorods increased with increasing growth time below 3 hr. The XRD results showed that ZnO nanorods were wurtzite-structured (hexagonal) ZnO.

Effect of Drawing Tubes without Interoperation Recrystallization Annealing on the Orientation of Boundaries Grain – Longitudinal Direction

well-aligned ZnO nanorod arrays (ZNRAs) grown on the ZnO seed layers coated p-silicon (p-Si) substrates in various times from 1.5 to 5 hr have been fabricated from aqueous solutions at low temperature. Morphologies, crystalline structure and optical transmission were investigated by a scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The results showed that ZNRAs grew vertically from the substrates, having uniform thickness and length distribution, the average diameters and length of ZnO nanorods increased with increasing growth time below 3 hr. The XRD results showed that ZnO nanorods were wurtzite-structured (hexagonal) ZnO.

Effect of Hydrothermal Reaction Conditions on the Sizes and Morphologies of ZnO Nanorods

The influence factors of hydrothermal treatment on the formation process of ZnO nanorods are investigated involving with hydrothermal temperature, time and precursor concentration. The as-obtained products were characterized by Scanning Electron microscope (SEM) and X-ray diffraction (XRD), respectively. XRD result indicates that the obtained ZnO nanorods are high-quality single crystals. SEM results indicate that both the diameter and the length of ZnO nanorods increase with increasing the hydrothermal time and temperature. The precursor concentration prominently determines the morphologies of ZnO nanostructure from initial particle morphology to rod-like, and to final slice-like morphology.

Effects of dye etching on the morphology and performance of ZnO nanorod dye-sensitized solar cells

Dye-sensitized solar cells based on electrodeposited ZnO nanorod arrays were fabricated and tested. Field-emission scanning electron microscopy (FESEM) and X-ray powder diffraction (XRD) were used to identify the characters of ZnO nanorod arrays. The effects of dye etching on the morphology and performance of ZnO nanorod dye-sensitized solar cells were studied. It was found that the surfaces of ZnO nanorods were both etched by dye solutions, no matter N3 or N719. Compared with N3, N719 had a larger damage to the structure of ZnO nanorod photoanode, and the photoelectric conversion efficiency of cells decreased quickly with the sensitizing time increasing. In a certain range, the increasing length of ZnO nanorods can clearly improve the photoelectric conversion efficiency of cells.

Effect of reaction time and Sb doping ratios on the architecturing of ZnO nanomaterials for gas sensor applications

ZnO nanostructures including nanorods and nanoparticles were synthesized via sol–gel technique. The factors were optimized in order to acquire undoped and doped ZnO that have nanorod morphological structures with high aspect ratio. Effect of reaction times (3, 6, 12, 24, and 48h) has been studied to optimize the best preparation conditions. The morphological structure, diameter and length of ZnO nanorods were determined using scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM). Nanoparticles of about 10nm and nanorods with diameter about 100nm were measured using (HRTEM). The maximum aspect ratio of nanorods has a value of 12 for 24h reaction times. X-ray diffraction (XRD) patterns for the as-synthesized ZnO nanopowders reveal a highly crystallized wurtzite structure. XRD also used for identifying phase structure and chemical state of ZnO and ZnO doped with Sb under different reaction times and different doping ratios. Chemical composition of the Sb-doped ZnO nanopowders was performed with energy dispersive X-ray (EDX) and inductive coupled plasma mass spectroscopy (ICP-AES), which also concluded the doping ratios of the reactions results. Effect of doping on the band gap values for ZnO nanopowders has been studied using UV–vis spectroscopy. The gas response of the homemade devices based on Sb-doped ZnO nanopowders toward O2, CO2 and Acetone vapor as a function of temperature was measured and compared with undoped ZnO films. The response and recovery times have been studied.

Controllable Template-Assisted Electrodeposition of Single- and Multi-Walled Nanotube Arrays for Electrochemical Energy Storage

Here we explored a novel ZnO nanorod array template-assisted electrodeposition route to synthesize large-scale single-walled polypyrrole (PPy) nanotube arrays (NTAs) and multi-walled MnO2/PPy/MnO2 NTAs. The structures of nanotubes, such as external and inner diameters, wall thicknesses, and lengths, can be well controlled by adjusting the diameters and lengths of ZnO nanorods and deposition time. The synthesized hybrid MnO2/PPy/MnO2 triple-walled nanotube arrays (TNTAs) as electrodes showed high supercapacitive perporties, excellent long-term cycling stability, and high energy and power densities. The PPy layers in MnO2/PPy/MnO2 TNTAs provide reliable electrical connections to MnO2 shells and uniquely serve as highly conductive cores to support the redox reactions in the active two-double MnO2 shells with highly electrolytic accessible surface area. The fabricated multi-walled NTAs allow high efficient utilization of electrode materials with facilitated transports of ions and electrons. The outstanding performance makes MnO2/PPy/MnO2 TNTAs promising candidates for supercapacitor electrodes.

Optimization of a New ZnO Nanorods Hydrothermal Synthesis Method for Solid State Dye Sensitized Solar Cells Applications

We report on the growth control of zinc oxide nanorods to point out the effect of the ZnO nanorods quality on the power conversion efficiency (PCE) of transparent conductive oxide (TCO)/ZnO nanorods/dye/spiro-OMeTAD/metal electrode photovoltaic devices. A promising PCE of 0.61% was measured for the best nanorods growth conditions. A careful control of all the growth parameters during the seeds layer deposition and the hydrothermal synthesis was necessary to reach such a high PCE for this kind of device. A regular nanorod layer with a flat upper surface was obtained for ethylenediamine to zinc acetate dihydrate molar ratio equal to 1.74 and a pH of 8.2. The growth was performed at 65 °C for 2 h to avoid zinc oxide brushes deposition on the surface, arising from zinc hydroxyacetate decomposition during the hydrothermal treatment. The effect of ZnO nanorods length (ranging from 1 to 3 μm) on solar cell efficiency was tested. Although the UV–vis absorption increases when the nanorods length increases, the bes...

Efficient and stable CH3NH3PbI3-sensitized ZnO nanorod array solid-state solar cells

We report for the first time the use of a perovskite (CH3NH3PbI3) absorber in combination with ZnO nanorod arrays (NRAs) for solar cell applications. The perovskite material has a higher absorption coefficient than molecular dye sensitizers, gives better solar cell stability, and is therefore more suited as a sensitizer for ZnO NRAs. A solar cell efficiency of 5.0% was achieved under 1000 W m(-2) AM 1.5 G illumination for a solar cell with the structure: ZnO NRA/CH3NH3PbI3/spiro-MeOTAD/Ag. Moreover, the solar cell shows a good long-term stability. Using transient photocurrent and photovoltage measurements it was found that the electron transport time and lifetime vary with the ZnO nanorod length, a trend which is similar to that in dye-sensitized solar cells, DSCs, suggesting a similar charge transfer process in ZnO NRA/CH3NH3PbI3 solar cells as in conventional DSCs. Compared to CH3NH3PbI3/TiO2 solar cells, ZnO shows a lower performance due to more recombination losses.