ZnO NRAs Research Articles

Patterned ZnO nanorods/indium sulfide based self-powered photoelectrochemical photodetectors

The present work reports the excellent alignment of zinc oxide nanorod arrays (ZnO NRAs) patterned via the maskless lithography technique which was used as a photoanode material for photoelectrochemical (PEC) photodetection applications. The effects of circular patterns having different diameters, different gaps between circles, and the utilization of indium sulfide (In2S3) as a light-absorbing material in the visible region have been investigated in the PEC photodetector (PD) system in two different electrolytes. PEC PD performance evaluation confirmed the positive effect of patterned ZnO NRAs-based photoanode in the presence of In2S3, enhancing 982.9 μAcm−2 of current density (Jphoto), 54.6 mA/W of responsivity (Rs), 1.98 × 1011 Jones of detectivity (D*) and 8.18 × 104 of selectivity (S%) values. Besides, the best-performing patterned ZnO NRAs/In2S3 has been used to construct a quasi-solid state assembly using the prepared ionic-gel electrolyte and consequently, 2.19 × 1011 Jones of D* value has been observed. After all, the proposed PEC PD devices exhibited fast rise/decay times(τr/τd) in millisecond extent at 400 nm of wavelength.

Enhanced photoelectrochemical performance of Bi2S3/Ag2S/ZnO novel ternary heterostructure nanorods

The current work investigates the morphology, crystallinity and photoelectrochemical (PEC) performance of bismuth sulfide/silver sulfide/zinc oxide nanorods (Bi2S3/Ag2S/ZnO NRAs) photoelectrodes as prepared at different annealing temperature. ZnO NRAs was initially grown hydrothermally, deposited in sequence with Ag2S and Bi2S3 via successive ionic layer adsorption and reaction (SILAR) method before undergoing the annealing treatment. The optimised photoelectrode (Bi2S3/Ag2S/ZnO NRAs-400 °C) possesses an optical bandgap of 1.60 eV extending the absorption edge of ZnO to visible light spectrum. The current-voltage characterization of Bi2S3/Ag2S/ZnO NRAs photoelectrodes revealed that the photocurrent density and photoconversion efficiency were strongly dependent on the annealing temperature. The PEC study shows that the photoelectrode annealed at 400 °C achieved impressive photocurrent density of 12.95 mA/cm2 at +0.5 V (vs Ag/AgCl/saturated KCl) under 100 mW/cm2 illumination with superior photoconversion efficiency of 12.63%. This improvement is due to the cascade-designed band structure alignment of Bi2S3/Ag2S/ZnO/ITO and to the brilliant role of Ag2S as an intermediate layer that reduced random chance of electron-hole (e−-h+) pairs recombination and improved the electrons collection efficiency. This work is highly anticipated to give contribution on further utilisation of Bi2S3/Ag2S/ZnO NRAs as a promising semiconductor material in PEC related applications.

Self-assembly of single-crystal ZnO nanorod arrays on flexible activated carbon fibers substrates and the superior photocatalytic degradation activity

The synthesis of one-dimensional nanocrystals on flexible substrates has attracted a great attention in the last decade. We here report an integrated approach using a sequential sol-gel and hydrothermal synthesis method to successfully assemble well-aligned single-crystalline wurtzite ZnO nanorod arrays (ZnO NRAs) on activated carbon fibers (ACFs). The ZnO NRAs, with high rod surface area (up to 20 m2 g−1), high aspect ratio (rod length/rod diameter, ca. 20:1) and high defect level (indicated by an extremely sharp blue emission, strong green and yellow emissions), were shown to grow nearly perpendicularly on the ACFs surface. The pre-coating of ZnO seed layers on ACFs surface during sol-gel synthesis is vital for the growth of the ordered ZnO nanorod arrays. The structural and optical properties of ZnO NRAs/ACFs can be adjusted by tuning the synthesis parameters for sol-gel and hydrothermal steps. As compared to the ZnO NRAs grown on the stiff substrates (e.g., silicon wafer, fluorine-doped tin oxide glass, GaN and metal sheets), ZnO NRAs grown on ACFs have very high surface area and intensive blue, green and yellow emissions. The novel ZnO NRAs/ACFs show excellent photocatalytic degradation of methylene blue and robust recyclability as compared to the individual ZnO nano particles (powder, NRs and NRAs).

Bismuth sulphide decorated ZnO nanorods heterostructure assembly via controlled SILAR cationic concentration for enhanced photoelectrochemical cells

The current study investigates Bi2S3 thin films coated on ZnO NRAs with varying cationic concentrations through ionic layer adsorption and reaction (SILAR) technique. XRD patterns reveal that Bi2S3 is successfully synthesised and exhibits orthorhombic structure on the wurtzite ZnO NRAs. The band gap energy (Eg) of Bi2S3/ZnO NRAs shows a notable red shift with increasing cationic concentration. The photocurrent density increases significantly with increasing concentration from 1 mM to 3 mM before decreases at higher concentration due to agglomeration of Bi2S3 NPs and formation of recombination centres. The hybrid photoanode Bi2S3/ZnO NRAs at 3 mM exhibits the highest photocurrent value (1.92 mA cm−2), which is about six times greater than that of plain ZnO NRAs (0.337 mA cm−2). The high photoconversion efficiency value of 1.65% versus 0.5 V Ag A−1g−1C−1l−1 is obtained by Bi2S3/ZnO NRAs (3 mM) in comparison with pristine ZnO NRs, mainly due to the stepwise band alignment edge and significant enhancement of morphological and optical properties. The study reveals that controlling the cationic concentration can potentially improve the photoconversion efficiency.

Enhanced photoresponse in ZnO nanorod array/p-GaN self-powered ultraviolet photodetectors via coupling with CuO nanostructures

ZnO nanorod arrays (ZnO NRAs) coupled with coral-like CuO nanostructures (CuO CLNs) were prepared by low-temperature hydrothermal method. Self-powered ultraviolet (UV) photodetectors (PDs) based on ZnO NRAs/CuO CLNs/p-GaN heterostructure were fabricated via a direct-contact method. Under UV illumination (1.46 mW cm−2), the ratios of photocurrent to dark current (Iphoto/Idark), photo-responsivity and specific detectivity for the ZnO NRAs/CuO CLNs/p-GaN heterojunction self-powered PD were estimated to be 1143, 1.44 mA W−1 and 5.9 × 1010 cm H z 1 /2/W at 0 V, which were about ∼187, ∼104 and ∼153 times greater than those of the ZnO NRAs/p-GaN self-powered PD, respectively. Moreover, the PD displayed faster response time, excellent stability and repeatability by coupling with CuO CLNs. The mechanism of the enhanced photoresponse performance was discussed through the energy band diagram.

Growth of highly uniform size-distribution ZnO NR arrays on sputtered ZnO thin film via hydrothermal with PMMA template assisted

This paper demonstrates a fabrication approach to control size distribution of zinc oxide nanorod arrays (ZnO NRAs) when using a polycrystalline seed layer. Through perfect matching between a physical confinement using a periodic PMMA template and a chemical confinement via hydrothermal method, highly ordered ZnO NRAs are accomplished. This matching relies on the restricted nucleation sites where the seed layer's grain size as well as number of grains along the template's aperture become dominant factors. In the experiment, various dimensions of periodic templates and precursor concentrations were carried on. The optimum condition shows single-ZnO NR arrays with good uniformity. Multiple rod array appears in the template with larger holes' dimension as it allows multiple nucleation sites to be formed. The effect of spacing between holes in the template is also included. The results demonstrate an effective and cost-effective way for tailoring uniformity of single ZnO NRAs on the polycrystalline seed layer.

ZnO nanorod arrays modified with Bi2S3 nanoparticles as cathode for efficient polymer solar cells

Abstract The surface modification of zinc oxide nanorod arrays (ZnO NRAs) is an effective way to improve electrical coupling between ZnO NRAs and organic active layer, and can decrease the surface defects of ZnO NRAs. In this work, ZnO NRAs grown on indium tin oxide (ITO) glass substrates are decorated with bismuth trisulphide (Bi2S3) nanoparticles using successive ionic layer adsorption and reaction (SILAR) at room temperature. The resulted ZnO/Bi2S3 core-shell NRAs are characterized by using different measurement techniques. SEM and TEM images confirm the homogeneous coverage of Bi2S3 nanoparticles on the surface of ZnO NRAs. XPS and PL spectra demonstrate that surface defects of ZnO NRAs modified with 0.2 mM Bi2S3 nanoparticles are effectively reduced. XRD spectra show the modification of the ZnO NRAs surface with Bi2S3 can enhances the crystallinity of the active layer and ZnO NRAs, which will improve the absorption of sunlight, and help for the charge transfer in solar cells. Finally, hybrid solar cells with the structure of ITO/ZnO/Bi2S3/P3HT:PC71BM (or PTB7:PC71BM)/MoO3/Ag are for the first time fabricated. The solar cells based on the ZnO/0.2 mM Bi2S3 core-shell NRAs with P3HT:PC71BM as active layer exhibit the nice performance with Jsc, Voc, FF and η values equal to 9.51 ± 0.09 mA/cm2, 0.61 ± 0.01 V, 61.6 ± 0.6%, and 3.57 ± 0.05%, respectively. Besides, the PCE of the device based on the ZnO/0.2 mM Bi2S3 core-shell NRAs with PTB7:PC71BM is improved to 6.35% from 4.88% of the reference device without Bi2S3 coated. Increase of electrical coupling between ZnO NRAs and organic active layer and decline of the surface defects of ZnO NRAs lead to the performance improvement of devices with ZnO/Bi2S3 core-shell NRAs, which implies that ZnO/Bi2S3 core-shell NRAs made by SILAR method are promising electron transport materials in solar cells.

Bismuth oxysulfide modified ZnO nanorod arrays as an efficient electron transport layer for inverted polymer solar cells

Vertically aligned zinc oxide nanorod arrays (ZnO NRAs) are expected to provide a direct and stable electron transport pathway in polymer solar cells (PSCs) so as to enhance charge carrier collection and transport.

Optimized preparation of Co-Pi decorated g-C3N4@ZnO shell-core nanorod array for its improved photoelectrochemical performance and stability

The cobalt-phosphate (Co-Pi) decorated g-C3N4@ZnO shell-core nanorod array (Co-Pi/g-C3N4@ZnO NRA) photoanode with broadened spectral response and optimized photoelectrochemical (PEC) performance was prepared. The g-C3N4@ZnO NRA was prepared via improved urea impregnation and calcination methods in semi enclosed environment. The g-C3N4 flexible slice shell was uniformly wrapped on ZnO nanorods core and the intimately contacted heterojunction was formed between the interface of g-C3N4 and ZnO. The g-C3N4@ZnO NRA promotes the separation and transfer of the photogenerated electron-hole pairs on g-C3N4 and ZnO under either visible light or white light illumination. The prepared g-C3N4@ZnO NRA was further electrodeposited with Co-Pi nanoparticles (NPs). The Co-Pi NPs can assist in the consumption of the photoinduced holes as well as pull the Fermi level potential of g-C3N4@ZnO NRAs towards the positive direction, resulting in the upward band bending at the band-edge position for Co-Pi/g-C3N4@ZnO NRAs and promoting the separation efficiency of the photogenerated electron-hole pairs. Consequently, the Co-Pi/g-C3N4@ZnO NRA exhibits an improved PEC performance under both visible light and white light illumination. In addition, g-C3N4 flexible slice shell decorated with Co-Pi NPs covered on the surface of ZnO NRAs core improved the stability of the ZnO NRA photoanode.

Tip-grafted Ag-ZnO nanorod arrays decorated with Au clusters for enhanced photocatalysis

Abstract The design and optimization of semiconductor-metal/metal cluster heterostructures are highly desirable for efficient photocatalytic redox reactions. Herein, Ag-tipped ZnO nanorod arrays decorated with glutathione-protected Au clusters (ZnO-Ag-Au NRAs) have been successfully prepared via photodeposition method and electrostatic self-assembly method, in which Ag nanoparticles are demonstrated to act as an electron mediator and Au clusters serve as a visible light photosensitizer to generate additional charge carriers in the composite photocatalyst. With selective tip growth of metallic Ag and surface decoration of Au clusters on ZnO NRAs, the as-obtained ZnO-Ag-Au NRAs operate to boost the charge separation and transfer, thereby showing the enhanced photocatalytic reduction of aqueous heavy metal ions. This work affords a feasible paradigm for the fine construction of tipped one-dimensional-based hybrid photocatalysts with enhanced activity toward the elimination of heavy metal pollutants from aqueous solutions.

Effect of heat treatment on photoelectrochemical performance of hydrothermally synthesised Ag2S/ZnO nanorods arrays

Low temperature hydrothermal method was used to produce a large surface area ZnO NRs on conductive glass. The same method was used to fabricate a photoelectrode of Ag2S quantum dots onto the nanorod arrays. Ag2S QDs/ZnO NRAs heterostructure was employed as photoanode in a standard 3-electrodes photoelectrochemical cell. A significant enhancement in the photoelectrochemical performance was observed for the Ag2S QDs/ZnO upon heat treatment 400 °C which displayed an impressive photoconversion efficiency of 4.08% by achieving ∼10-times higher compared to bare ZnO NRAs. This enhancement was attributed to the improved morphological structure, crystallinity and optical properties of the synthesised heterostructures.

Blocking the Formation of Zn2+/Dye Complexes in Dye-Sensitized Solar Cells by Inserting CdS Quantum Dots into Sandwich Layer

ZnO NRAs are grown on ITO substrates by a simple chemical method. CdS QDs were deposited on ZnO NRAs by SILAR. N719 was synthesized by dipping method. J–V analysis indicates that by inserting a layer of CdS QDs, the conversion efficiency of DSSCs was improved obviously. The device with CdS QDs shows the higher conversion efficiency due to the three reasons: (1) CdS QDs enhanced adsorption spectra of DSSCs in the visible region; (2) CdS QDs block the formation of Zn2+/dye complex, it is beneficial for electros transport from dye to ZnO photoanode. It is the key to obtain higher conversion efficiency; (3) FRET dynamics exists by the introduction of CdS QDs.

Facile Construction of Dual p-n Junctions in CdS/Cu2O/ZnO Photoanode with Enhanced Charge Carrier Separation and Transfer Ability.

With the gradually increasing demand for solving the environmental pollution problem and energy crisis, efficient photocatalysts with superior charge carrier separation and transfer ability have attracted extensive research attention. Herein, n-type CdS-decorated p-Cu2O/n-ZnO nanorod arrays (CdS/Cu2O/ZnO NRAs), integrating the merits of both highly ordered structure and synergistic effect derived from dual p–n junctions, were successfully fabricated and further applied to photoelectrocatalysis. In this ternary nanocomposite, fast generation, separation, and transfer of charge carriers were achieved in the Cu2O/ZnO and Cu2O/CdS dual p–n junction regions due to their built-in electric field and appropriate band structures. Moreover, both highly ordered ZnO NRAs and compact CdS shell play the role of an electron collector and a transport channel that efficiently consumes the photoinduced electrons in the conduction band of Cu2O, which considerably reduces the recombination rate of charge carriers. As expected, the perfect cooperation of the three participators leads to the highest photoconversion efficiency of 2.61% at −0.275 V (versus saturated calomel electrode) and an incident photon-to-current conversion efficiency of 14.51% at 380 nm as well as the photoelectrocatalytic degradation ability of the optimized 30 min CdS/Cu2O/ZnO NRAs photoanode as compared to that of the Cu2O/ZnO and ZnO NRAs photoanodes. It is believed that the induced synergistic effect between dual p–n junctions and ZnO NRAs caused the superior performances of the CdS/Cu2O/ZnO NRAs photoanode, and this ternary material with a unique structure may present a new way of thinking for potential applications in the photoelectrochemistry field.

Performance improvement of ZnO/P3HT hybrid UV photo-detector by interfacial Au nanolayer

In this study, a hybrid ultraviolet (UV) photo detector comprising of hydrothermally grown highly oriented Zinc Oxide nanorod arrays (ZnO NRAs) and Poly(3-hexylthiophene-2,5-diyl) (P3HT) as an active layer was fabricated and characterized. These hybrid photo detectors demonstrated a high rectification ratio (∼117) and responsivity of 10.7A/W at −2V under incident light of wavelength 325nm. Further to investigate the effect of surface plasmon property of metal nanoparticles on the performance of hybrid UV photo detectors, ZnO NRAs were capped with dc sputtered gold (Au) metal nanolayer (∼5nm) at the ZnO-P3HT interface, prior to coating P3HT layer on top of it. It was found out that upon Au coating the absorption of the ZnO was enhanced partly in the ultraviolet and visible region. In consequence the rectification ratio and responsivity of the hybrid photo detector was enhanced drastically from 117 to 1167 and 10.7 to 17.7A/W respectively. Interestingly the reduction in dark current was observed on Au coating and it was revealed that Au nanoparticles play a key role in enhancing the performance of the hybrid photo detectors.

ZnO nanorod arrays and direct wire bonding on GaN surfaces for rapid fabrication of antireflective, high-temperature ultraviolet sensors

Rapid, cost-effective, and simple fabrication/packaging of microscale gallium nitride (GaN) ultraviolet (UV) sensors are demonstrated using zinc oxide nanorod arrays (ZnO NRAs) as an antireflective layer and direct bonding of aluminum wires to the GaN surface. The presence of the ZnO NRAs on the GaN surface significantly reduced the reflectance to less than 1% in the UV and 4% in the visible light region. As a result, the devices fabricated with ZnO NRAs and mechanically stable aluminum bonding wires (pull strength of 3–5gf) showed higher sensitivity (136.3% at room temperature and 148.2% increase at 250°C) when compared with devices with bare (uncoated) GaN surfaces. In addition, the devices demonstrated reliable operation at high temperatures up to 300°C, supporting the feasibility of simple and cost-effective UV sensors operating with higher sensitivity in high-temperature conditions, such as in combustion, downhole, and space exploration applications.

Effect of AZO film as seeding substrate on the electrodeposition and properties of Al-doped ZnO nanorod arrays

The fabrication of whole Al-doped ZnO nanostructured electrodes is reported by a two-step technology. Magnetron sputtered Al-doped ZnO (AZO) films were investigated as seeding substrates for the electrodeposition of Al-doped ZnO nanorod arrays. The nucleation, density, morphological and structural properties of Al-doped ZnO NRAs were analyzed as a function of precursor concentration and substrate and compared to undoped ZnO NRAs. High density and good crystal quality are reported for the Al-doped ZnO NRAs grown on AZO films from low precursor concentration.

Structural and optical properties of ZnO nanorods by electrochemical growth using multi-walled carbon nanotube-composed seed layers

We reported the enhancement of the structural and optical properties of electrochemically synthesized zinc oxide [ZnO] nanorod arrays [NRAs] using the multi-walled carbon nanotube [MWCNT]-composed seed layers, which were formed by spin-coating the aqueous seed solution containing MWCNTs on the indium tin oxide-coated glass substrate. The MWCNT-composed seed layer served as the efficient nucleation surface as well as the film with better electrical conductivity, thus leading to a more uniform high-density ZnO NRAs with an improved crystal quality during the electrochemical deposition process. For ZnO NRAs grown on the seed layer containing MWCNTs (2 wt.%), the photoluminescence peak intensity of the near-band-edge emission at a wavelength of approximately 375 nm was enhanced by 2.8 times compared with that of the ZnO nanorods grown without the seed layer due to the high crystallinity of ZnO NRAs and the surface plasmon-meditated emission enhancement by MWCNTs. The effect of the MWCNT-composed seed layer on the surface wettability was also investigated.PACS: 81.07.-b; 81.16.-c; 81.07.Pr; 61.48.De.

Giant Efficiency Enhancement of GaAs Solar Cells with Graded Antireflection Layers Based on Syringelike ZnO Nanorod Arrays

An effective antireflection coating of syringelike ZnO NRAs is demonstrated for GaAs solar cells. Energy conversion efficiency is significantly enhanced by up to 32%. GaAs is focussed on as a model system, but the hydrothermal growth of syringelike ZnO nanostructures is readily compatible with the existing processes in the photovoltaic industry, and highly applicable for various types of solar cells.