Cost Effective Solvothermal Method to Synthesize Zn-Doped TiO2 Nanomaterials for Photovoltaic and Photocatalytic Degradation Applications

Titanium dioxide (TiO2) is a commonly used wide bandgap semiconductor material for energy and environmental applications. Although it is a promising candidate for photovoltaic and photocatalytic applications, its overall performance is still limited due to low mobility of porous TiO2 and its limited spectral response. This limitation can be overcome by several ways, one of which is doping that could be used to improve the light harvesting properties of TiO2 by tuning its bandgap. TiO2 doped with elements, such as alkali-earth metals, transition metals, rare-earth elements, and nonmetals, were found to improve its performance in the photovoltaic and photocatalytic applications. Among the doped TiO2 nanomaterials, transition metal doped TiO2 nanomaterials perform efficiently by suppressing the relaxation and recombination of charge carriers and improving the absorption of light in the visible region. This work reports the possibility of enhancing the performance of TiO2 towards Dye Sensitised Solar Cells (DSSCs) and photocatalytic degradation of methylene blue (MB) by employing Zn doping on TiO2 nanomaterials. Zn doping was carried out by varying the mole percentage of Zn on TiO2 by a facile solvothermal method and the synthesized nanomaterials were characterised. The XRD (X-Ray Diffraction) studies confirmed the presence of anatase phase of TiO2 in the synthesized nanomaterials, unaffected by Zn doping. The UV-Visible spectrum of Zn-doped TiO2 showed a red shift which could be attributed to the reduced bandgap resulted by Zn doping. Significant enhancement in Power Conversion Efficiency (PCE) was observed with 1.0 mol% Zn-doped TiO2 based DSSC, which was 35% greater than that of the control device. In addition, it showed complete degradation of MB within 3 h of light illumination and rate constant of 1.5466×10−4s−1 resembling zeroth order reaction. These improvements are attributed to the reduced bandgap energy and the reduced charge recombination by Zn doping on TiO2.

Optimization of Aluminium Doping Concentration in Titanium Dioxide Nanoparticles Photo Anode for Enhancing Efficiency of Dye-Sensitized Solar Cell

Well crystallized Aluminium (Al) doped Titanium dioxide (TiO2) nanoparticles with various doping concentration (0, 0.05[Formula: see text]M, 0.07[Formula: see text]M, 0.09[Formula: see text]M and 0.11[Formula: see text]M) were synthesized successfully by sol–gel route to develop the photo anode of Dye Sensitized Solar Cell (DSSC). Anatase crystalline nature of TiO2 nanoparticles was confirmed using X-ray diffraction (XRD) and Raman spectrophotometer. The Atomic Force Microscopy (AFM) was used to investigate the morphology of the photo anode (Al-doped TiO2 nanoparticles). The photovoltaic performance of the DSSC in terms of Current, Voltage and efficiency was investigated with a standard illumination of AM1.5G having an irradiance 100[Formula: see text]mW/cm2. Optimized values of Short Circuit Current density ([Formula: see text]), Open Circuit Voltage ([Formula: see text]) and efficiency ([Formula: see text]) obtained was 247.62[Formula: see text][Formula: see text]A/cm2, 359[Formula: see text]mV and 0.02456%, respectively for 0.07[Formula: see text]M Al doping concentration. Eco-friendly Eosin Y dye was used for sensitization of the photo anode. The optimized photovoltaic cell exhibits very good efficiency (80.05% more than the earlier reported work).

Preferentially oriented TiO2 nanotube arrays on non-native substrates and their improved performance as electron transporting layer in halide perovskite solar cells

Anodically formed TiO₂ nanotube arrays (TNTAs) constitute an optoelectronic platform that is being studied for use as a photoanode in photoelectrocatalytic cells, as an electron transport layer (ETL) in solar cells and photodetectors, and as an active layer for chemiresistive and microwave sensors. For optimal transport of charge carriers in these one-dimensional polycrystalline ordered structures, it is desirable to introduce a preferential texture with the grains constituting the nanotube walls aligned along the transport direction. Through x-ray diffraction analysis, we demonstrate that choosing the right water content in the anodization electrolyte and the use of a post-anodization zinc ion treatment can introduce a preferential texture in sub-micron length transparent TNTAs formed on non-native substrates. The incorporation of 1.5 atom% of Zn in TiO₂ nanotubes prior to annealing, was found to consistently result in the strongest preferential orientation along the [001] direction. [001] oriented TNTAs exhibited a responsivity of 523 A W^-1 at a bias of 2 V for 365 nm photons, which is among the highest reported performance values for ultraviolet photodetection using titania nanotubes. Furthermore, the textured nanotubes without a Zn²⁺ treatment showed a significantly enhanced performance in halide perovskite solar cells that used TNTAs as the ETL.

Photocatalysis and Hydrogen Evolution of Al- and Zn-Doped TiO2 Nanotubes Fabricated by Atomic Layer Deposition

Highly homogeneous Al- and Zn-doped TiO₂ nanotubes were fabricated by atomic layer deposition (ALD) via nanolaminated stacks of binary layers of TiO₂/Al₂O₃ and TiO₂/ZnO, respectively. The bilayers were alternately deposited on the polycarbonate (PC) membrane template by ALD with various cyclic sequences. The nanotubes in a length of 20 μm and a diameter of 220 nm were obtained after removal of the PC membrane by annealing at 450 °C. The effects of doping composition on the photocatalytic and photoelectrochemical (PEC) activities were investigated. Increasing the Al doping reduced the photocatalytic activity of TiO₂ due to formation of charge recombination sites and reduction of hydroxide radicals. In contrast, there was an optimal range of Zn doping to get enhanced photocatalytic activity and higher PEC efficiency. With a doping ratio of 0.01, the hydrogen production rate from water splitting was 6 times higher than that of commercial P25 TiO₂. The energy-band diagram of Zn-doped TiO₂ determined by ultraviolet photoelectron spectroscopy revealed shift up of the Fermi level to provide more electrons to the conduction band. The photoinduced trapped electrons and holes were detected in Zn-doped TiO₂ by in situ electron paramagnetic resonance spectroscopy, which revealed that Ti³⁺ sites on the surface and surface oxygen vacancies played a key role in promoting the photocatalytic process.

Mechanism of H adatoms improving the O2 reduction reaction on the Zn-modified anatase TiO2 (101) surface studied by first principles calculation

Surface H and subsurface Zn interstitials could facilitate O₂ adsorption and dissociation on the TiO₂ surface.

Prolonged lifetime and retarded recombination in dye sensitized solar cells using hydrogenated fluorine doped TiO2 nanocrystals as a photoanode

Novel HF-TiO₂ nanoparticles are synthesized using an annealing method and applied in dye sensitized solar cells as an excellent photoanode nanomaterial.

A graphene oxide incorporated TiO2 photoanode for high efficiency quasi solid state dye sensitized solar cells based on a poly-vinyl alcohol gel electrolyte

An effective self assembly method was used to synthesize hybrid nanocomposites of TiO₂ nanoparticles on graphene oxide (GO) sheets for application in Dye Sensitized Solar Cells (DSSCs).

Enabling high solubility of ZnO in TiO₂ by nanolamination of atomic layer deposition

Zn-doped TiO2 nanotubes were fabricated by nanolaminated packing of alternating layers of TiO2 and ZnO by atomic layer deposition (ALD) using a polycarbonate (PC) membrane as a template. With 400 cycles of ALD, the nanotubes with a thickness of 28 nm and an outer diameter of 220 nm were obtained after removing the PC membrane by annealing at 450 °C. The doping concentration of ZnO in TiO2 depends on the precursor cycle ratio of ZnO to TiO2. With the precursor cycle ratio of ZnO : TiO2 at 0.04, a uniform bulk solubility of ∼8 at% is obtained, and the surface concentration of Zn is even higher, ∼16 at%. From the depth profiles measured by secondary ion mass spectrometry, Zn is uniformly distributed across the thickness, which is further confirmed by analyses of X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. Additionally, from the transmission electron microscopic observation, the highly doped anatase TiO2 exhibits some regions of severe deformation that results in localized solid-state amorphization.

Physical properties of Zn doped TiO2 thin films with spray pyrolysis technique and its effects in antibacterial activity

Zinc doped Titanium dioxide (TiO2: Zn) thin films were deposited onto glass substrates by the spray pyrolysis technique with the substrate temperature 450°C. The structural, optical, photoluminescence (PL) properties and morphological studies were investigated for the films deposited with various doping concentration (0, 2, 4, 6 and 8at.%) of zinc. The results of X-ray diffraction (XRD) had shown the presence of anatase peak with a strong orientation along (101) plane at 8at.% of Zn-doped TiO2 film. Scanning electron microscopy (SEM) study showed the uniform distribution of grains with porous nature. Atomic force microscopy (AFM) observations indicated the tetragonal shape at 8at.% of Zn-doped TiO2 with the particle size and decrease in surface roughness. The emission at 398nm was observed at the 8at.% of Zn-doped TiO2 thin film. The carrier concentration and Hall mobility was increased with doping. The antibacterial activity was highly yielded for the Zn-doped TiO2 thin films.

A facile and general synthesis strategy to doped TiO2 nanoaggregates with a mesoporous structure and comparable property

A facile and general route was explored to fabricate porous metal-doped TiO₂ nanoaggregates from a titanium glycolate precursor and metal salts, and doping with Co or Ni is an effective approach to improve the photocatalytic efficiency.

Tailoring the conduction band of titanium oxide by doping tungsten for efficient electron injection in a sensitized photoanode

Aiming to overcome the current limits for dye-sensitized solar cells (DSSC) to reach a higher solar energy conversion efficiency, this work set out to investigate the feasibility of combining a variety of preparation techniques that can finely tailor the optical and electrochemical properties of the photoanode material. The obtained tungsten doped mesoporous titania spheres exhibited significant enhancements of photocurrent and open-circuit voltage leading to an over 15% increase in cell efficiency. With a single layer 12 μm film, the W-doped photoanode reached a solar energy conversion efficiency of 8.9% which is far greater than a 5.7% efficiency obtained by the photoanode film prepared from Degussa P25 TiO2 nanoparticles. This was greatly attributed to the superior light scattering effect from the mesostructure and the increased electron injection driving-force from the down-shifted conduction band after doping.

Porous (001)-faceted Zn-doped anatase TiO2 nanowalls and their heterogeneous photocatalytic characterization

Porous and single-crystal Zn-doped TiO₂ nanowall with (001) lattice-plane can be grown on indium tin oxide substrate using a liquid-phase deposition method. The present structure promises potential uses in solar cells and photocatalysis.

Novel preparation of anatase TiO2@reduced graphene oxide hybrids for high-performance dye-sensitized solar cells

An effective method was developed to prepare hybrid materials of TiO2 nanoparticles on reduced graphene oxide (RGO) sheets for application in solar cells. The morphology, size, and crystal phase of the TiO2 nanoparticles and TiO2@reduced graphene oxide (TiO2@RGO) hybrids were investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), Raman, and UV-vis diffuse reflectance spectroscopy. A possible growth mechanism of TiO2@RGO hybrids is proposed based on observations of the TiO2 nanoparticles obtained from the hydrolysis process under different conditions. The effects of different reduced graphene oxide contents on the energy conversion efficiency of the dye-sensitized solar cells (DSSCs) based on J-V and incident photon-to-current conversion efficiency (IPCE) spectra are also discussed. DSSCs based on TiO2@RGO hybrid photoanodes with a graphene content of 1.6 wt % showed an overall light-to-electricity conversion efficiency of 7.68%, which is much higher than that of pure anatase nanoparticles (4.78%) accompanied by a short-circuit current density of 18.39 mA cm(2), an open-circuit voltage of 0.682 V, and a fill factor of 61.2%.