Low temperature grown ZnO@TiO2 core shell nanorod arrays for dye sensitized solar cell application

Fabrication of porous and visible light active ZnO nanorods and ZnO@TiO2 core-shell photocatalysts for self-cleaning applications

Highly transparent and self-cleaning ZnO nanorods (NRs) and ZnO@TiO₂ core-shell (CS) nanoarrays were fabricated using the sol-gel dip-coating technique. TiO₂ nanoparticles (NPs) were coated as a shell layer over the hydrothermally grown ZnO NRs. The number of shell layers on the ZnO NRs was varied by modulating the number of dipping cycles from 1 to 3 to optimize their transmittance. The optimized CS nanoarrays with two dipping cycles display a 2% enhancement of optical transmission compared to the ZnO NRs. In addition, superhydrophilicity (contact angle ∼of 12°) stimulates the self-cleaning nature of the thin films. A water contact angle of 12° was noted for the ZnO@TiO₂: 2 cycle sample, indicating their superhydrophilic nature. Moreover, the photocatalytic activity of the pristine ZnO NRs and ZnO@TiO₂ CS nanoarrays was tested under UV and direct sunlight through the dye degradation of methylene blue (MB). Based upon the TiO₂ morphology and accessibility of the ZnO@TiO₂ heterojunction interface, CS nanoarrays with two shell layers exhibit the highest degree of dye photodegradation efficiency of 68.72% and 91% under sunlight and UV light irradiation, respectively. The CS nanoarrays demonstrate medium sunlight and excellent UV-light-driven photocatalytic activity. Our findings suggest that the ZnO@TiO₂ CS nanoarrays are potential photocatalysts for dye degradation and self-cleaning applications in solar cell coverings.

Preparation and UV Photoelectric Properties of Aligned ZnO-TiO2 and TiO2-ZnO Core-Shell Structured Heterojunction Nanotubes

Large-area horizontal-aligned ZnO nanotubes (ZNTs), TiO₂ nanotubes (TNTs), TiO₂-ZnO core-shell nanotubes (TZNTs) and ZnO-TiO₂ core-shell nanotubes (ZTNTs) were successfully synthesized by electrospinning combined with pulsed-laser deposition. The morphology, structure, and composition of the samples were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The photoluminescence (PL) spectra of these samples indicate that the addition of a TiO₂ layer greatly decreases the recombination of photogenerated carriers in the heterojunction nanotubes. The photodetectors (PDs) were fabricated by assembling horizontally ordered nanotubes on the gold interdigital electrode, and their ultraviolet (UV) detection performances were compared. The test results at room temperature show that the PD with aligned ZTNTs have the best UV response and a short response recovery time. In addition, the performance of ZTNT PDs and TZNT PDs are further improved under heating. The photo/dark current ratio, responsivity (R_λ), detectivity (D*), and external quantum efficiency (EQE) of ZTNTs increased to 388, 450 uA·W^-1, 1.1 × 10¹⁰ cm·Hz^1/2·W^-1, and 0.15%, respectively, under the condition of 365 nm UV radiation with a power density of 4.9 mW·cm^-2 and a 1 V bias at 90 °C. The UV response mechanism and structural superiority of the horizontally ordered coaxial heteronanotube were also discussed. In addition, this work provides an important method for the design of other ordered nanomaterials and structures, which have a wide range of applications in the fields of sensors, transistors, transparent flexible electrodes, and other multifunctional devices.

Titanium Dioxide-Coated Zinc Oxide Nanorods as an Efficient Photoelectrode in Dye-Sensitized Solar Cells

Well-arrayed zinc oxide nanorods applied as photoelectrodes for dye-sensitized solar cells were synthesized on an aluminum-doped zinc oxide substrate by the multi-annealing method. In order to improve the chemical stability and surface-to-volume ratio of photoanodes in dye-sensitized solar cells, the synthesized zinc oxide nanorods were coated with pure anatase phase titanium dioxide film using a novel mist chemical vapor deposition method. The effects of the titanium dioxide film on the morphological, structural, optical, and photovoltaic properties of zinc oxide–titanium dioxide core–shell nanorods were investigated. It was found that the diameter and surface-to-volume ratio of zinc oxide nanorods were significantly increased by coating them with titanium dioxide thin film. The power conversion efficiency of dye-sensitized solar cells was improved from 1.31% to 2.68% by coating titanium dioxide film onto the surface of zinc oxide nanorods.

Bio-inspired mineralization of nanostructured TiO2 on PET and FTO films with high surface area and high photocatalytic activity

Nanostructured TiO₂ coatings were successfully formed on polyethylene terephthalate (PET) films and fluorine-doped tin oxide (FTO) films in aqueous solutions. They contained an assembly of nanoneedles that grow perpendicular to the films. The surface area of the coatings on PET films reached around 284 times that of a bare PET film. Micro-, nano-, or subnanosized surface roughness and inside pores contributed to the high nitrogen adsorption. The coatings on FTO films showed an acetaldehyde removal rate of 2.80 μmol/h; this value is similar to those of commercial products certified by the Photocatalysis Industry Association of Japan. The rate increased greatly to 10.16 μmol/h upon annealing in air at 500 °C for 4 h; this value exceeded those of commercial products. Further, the coatings showed a NO_x removal rate of 1.04 μmol/h; this value is similar to those of commercial products. The rate decreased to 0.42 μmol/h upon annealing. NO_x removal was affected by the photocatalyst’s surface area rather than its crystallinity.

TiO2 Coated ZnO Nanorods by Mist Chemical Vapor Deposition for Application as Photoanodes for Dye-Sensitized Solar Cells

In this study, a mist chemical vapor deposition method was applied to create a coating of titanium dioxide particles in order to fabricate ZnO/TiO₂ core-shell nanostructures. The thin layers of titanium dioxide on the zinc oxide nanorods were uniform and confirmed as pure anatase phase. The morphological, structural, optical and photoluminescence properties of the ZnO/TiO₂ core-shell structures were influenced by coating time. For instance, the crystallinity of the titanium dioxide increased in accordance with an increase in the duration of the coating time. Additionally, the thickness of the titanium dioxide layer gradually increased with the coating time, resulting in an increased surface area. The transmittance of the arrayed ZnO/TiO₂ core-shell structures was 65% after 15 min of coating. The obtained ZnO/TiO₂ core-shell nanostructures demonstrated high potentiality to serve as photoanodes for application in dye-sensitized solar cells.

ZnO nanowires for solar cells: a comprehensive review

As an abundant and non-toxic wide band gap semiconductor with a high electron mobility, ZnO in the form of nanowires (NWs) has emerged as an important electron transporting material in a vast number of nanostructured solar cells. ZnO NWs are grown by low-cost chemical deposition techniques and their integration into solar cells presents, in principle, significant advantages including efficient optical absorption through light trapping phenomena and enhanced charge carrier separation and collection. However, they also raise some significant issues related to the control of the interface properties and to the technological integration. The present review is intended to report a detailed analysis of the state-of-the-art of all types of nanostructured solar cells integrating ZnO NWs, including extremely thin absorber solar cells, quantum dot solar cells, dye-sensitized solar cells, organic and hybrid solar cells, as well as halide perovskite-based solar cells.

Eosin-Y sensitized core-shell TiO2-ZnO nano-structured photoanodes for dye-sensitized solar cell applications

In the current investigation, TiO₂ and TiO₂-ZnO (core-shell) spherical nanoparticles were synthesized by simple combined hydrolysis and refluxing method. A TiO₂ core nanomaterial on the shell material of ZnO was synthesized by utilizing variable ratios of ZnO. The structural characterization of TiO₂-ZnO core/shell nanoparticles were done by XRD analysis. The spherical structured morphology of the TiO₂-ZnO has been confirmed through field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) studies. The UV-visible spectra of TiO₂-ZnO nanostructures were also compared with the pristine TiO₂ to investigate the shift of wavelength. The TiO₂-ZnO core/shell nanoparticles at the interface efficiently collect the photogenarated electrons from ZnO and also ZnO act a barrier for reduced charge recombination of electrolyte and dye-nanoparticles interface. This combination improved the light absorption which induced the charge transfer ability and dye loading capacity of core-shell nanoparticles. An enhancement in the short circuit current (J_sc) from 1.67 mA/cm² to 2.1 mA/cm² has been observed for TiO₂-ZnObased photoanode (with platinum free counter electrode), promises an improvement in the energy conversion efficiency by 57% in comparison with that of the DSSCs based on the pristine TiO₂. Henceforth, TiO₂-ZnO photoelectrode in ZnO will effectively act as barrier at the interface of TiO₂-ZnO and TiO₂, ensuring the potential for DSSC application.