Ferromagnetism and Ru-Ru distance in SrRuO3 thin film grown on SrTiO3 (111) substrate

TiO₂ hierarchical nanostructures with secondary growth have been successfully synthesized on electrospun nanofibers via surfactant-free hydrothermal route. The effect of hydrothermal reaction time on the secondary nanostructures has been studied. The synthesized nanostructures comprise electrospun nanofibers which are polycrystalline with anatase phase and have single crystalline, rutile TiO₂ nanorod-like structures growing on them. These secondary nanostructures have a preferential growth direction [110]. UV–vis spectroscopy measurements point to better dye loading capability and incident photon to current conversion efficiency spectra show enhanced light harvesting of the synthesized hierarchical structures. Concomitantly, the dye molecules act as spacers between the conduction band electrons of TiO₂ and holes in the hole transporting medium, i.e., spiro-OMeTAD and thus enhance open circuit voltage. The charge transport and recombination effects are characterized by electrochemical impedance spectroscopy measurements. As a result of improved light harvesting, dye loading, and reduced recombination losses, the hierarchical nanofibers yield 2.14% electrochemical conversion efficiency which is 50% higher than the efficiency obtained by plain nanofibers.     

Improved dye-sensitized solar cell with a ZnO nanotree photoanode by hydrothermal method

This study investigated the influence of ZnO nanostructures on dye adsorption to increase the photovoltaic conversion efficiency of solar cells. ZnO nanostructures were grown in both tree-like and nanorod (NR) arrays on an AZO/FTO film structure by using a hydrothermal method. The results were observed in detail using X-ray diffraction, field-emission scanning electron microscopy (FE-SEM), UV-visible spectrophotometry, electrochemical impedance spectroscopy, and solar simulation. The selective growth of tree-like ZnO was found to exhibit higher dye adsorption loading and conversion efficiency than ZnO NRs. The multiple ‘branches’ of ‘tree-like nanostructures’ increases the surface area for higher light harvesting and dye loading while reducing charge recombination. These improvements result in a 15% enhancement in power conversion. The objective of this study is to facilitate the development of a ZnO-based dye-sensitized solar cell.     

The influence of anatase-rutile mixed phase and ZnO blocking layer on dye-sensitized solar cells based on TiO2nanofiberphotoanodes

High performance is expected in dye-sensitized solar cells (DSSCs) that utilize one-dimensional (1-D) TiO₂ nanostructures owing to the effective electron transport. However, due to the low dye adsorption, mainly because of their smooth surfaces, 1-D TiO₂ DSSCs show relatively lower efficiencies than nanoparticle-based ones. Herein, we demonstrate a very simple approach using thick TiO₂ electrospun nanofiber films as photoanodes to obtain high conversion efficiency. To improve the performance of the DSCCs, anatase-rutile mixed-phase TiO₂ nanofibers are achieved by increasing sintering temperature above 500°C, and very thin ZnO films are deposited by atomic layer deposition (ALD) method as blocking layers. With approximately 40-μm-thick mixed-phase (approximately 15.6?wt.% rutile) TiO₂ nanofiber as photoanode and 15-nm-thick compact ZnO film as a blocking layer in DSSC, the photoelectric conversion efficiency and short-circuit current are measured as 8.01% and 17.3?mA?cm^?2, respectively. Intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy measurements reveal that extremely large electron diffusion length is the key point to support the usage of thick TiO₂ nanofibers as photoanodes with very thin ZnO blocking layers to obtain high photocurrents and high conversion efficiencies.     

Enhanced electron collection efficiency of nanostructured dye‐sensitized solar cells by incorporating TiO2 cubes

Herein, enhancement of dye‐sensitized solar cell (DSC) performance is reported by combining the merits of the dye loading of TiO₂ nanoparticles and light scattering, straight carrier transport path, and efficient electron collection efficiency of TiO₂ cubes. We fabricate DSC devices with various arrangement styles and compositions of the electrodes in the forms of monolayer and double layer films. For this purpose, the solvothermal synthesized TiO₂ cubic particles (100‐600 nm) are employed as the scattering layer, whereas TiO₂ nanoparticles (15‐30 nm) synthesized via a combination of solvothermal and sol‐gel routes are used as the active layer of devices. We improve the photovoltaic characteristics of DSCs by two mechanisms. First, the light harvesting of DSC devices made of nanoparticles is improved by controlling the thickness of monolayer films, reaching the highest efficiency of 7.0%. Second, the light scattering and electron collection efficiency are enhanced by controlling the composition of double layer films composed of mixtures of TiO₂ nanoparticles and cubes, obtaining the maximum efficiency of 8.21%. The enhancements are attributed to balance between charge transfer resistance and charge recombination of photo‐generated electrons as well as dye loading and light scattering.     

Novel ZnO microflowers on nanorod arrays: local dissolution-driven growth and enhanced light harvesting in dye-sensitized solar cells

ZnO nanostructures were manipulated, via a low-temperature solution process, from pure nanorod arrays to complex nanostructures of microflowers on nanorod arrays with adjusted quantities of flowers. We proposed the mechanism of local dissolution-driven growth to rationally discuss the novel growth process. These nanostructures were used as photoanodes in dye-sensitized solar cells. Compared to pure nanorod arrays, the nanorod array-microflower hierarchical structures improved the power conversion efficiency from 0.41% to 0.92%, corresponding to a 124% efficiency increase. The enhancement of the efficiency was mainly ascribed to the synergistic effect of the enhanced surface area for higher dye loading and the improved light harvesting from efficient light scattering. Present results provide a promising route to improve the capability of light-harvesting for ZnO nanorod array-based DSSCs.     

Ultrasonic assisted synthesis of TiO2–reduced graphene oxide nanocomposites with superior photovoltaic and photocatalytic activities

In this work, TiO₂–reduced graphene oxide (RGO) nanocomposites were successfully produced by an ultrasonication-assisted reduction process. The reduction of graphene oxide (GO) and the formation TiO₂ crystals occurred simultaneously. The synthesized nanocomposite was characterized by SEM, EDX, Raman spectroscopy, FTIR, XRD, XPS, UV–vis spectroscopy, photoluminescence spectrometer and electrochemical impedance spectroscopy. As a result of the introduction of RGO, the light absorption of octahedral TiO₂ was markedly improved. The photocatalytic results revealed that weight percent of RGO has substantial influence on degradation of Rhodamine B under visible light irradiation. The enhancement of the photocatalytic activity can be attributed to the enhancement of the visible-light irradiation harvesting and efficiently separation of the photogenerated charge carriers. Meanwhile, upon the RGO loading, the photoelectric conversion efficiency of TiO₂–RGO nanocomposite modified electrode was also highly improved.     

Synergetic effect of graphene sheet and three‐dimensional crumpled graphene on the performance of dye‐sensitized solar cells

Herein, an improved structure of the dye‐sensitized solar cell (DSSC) is demonstrated which is composed of surface modified fluorine‐doped tin oxide (FTO) glass with graphene (GR) sheets and TiO₂ films incorporated with three‐dimensional crumped graphene (3‐D CGR)/GR sheets. The morphologies of the as‐prepared GR sheets on FTO glasses and 3‐D CGR/GR sheets/TiO₂ films were observed by field‐emission scanning electron microscopy. Light harvesting and charge recombination kinetics were investigated with a solar simulator and electrochemical impedance spectroscopy analysis. In addition to the reduced charge resistance by the GR modified FTO, the enhanced dye loading capability of the 3‐D CGR, and the rapid charge transport by the 2‐D GR sheets, the power conversion efficiency was 7.2%, which was an increase of 56% compared to a “conventional” structured DSSC. © 2015 American Institute of Chemical Engineers AIChE J, 62: 574–579, 2016     

TiO2‐Modified Flower‐Like Bi2WO6 Nanostructures with Enhanced UV‐Vis Photocatalytic Activity

Anatase TiO₂‐modified flower‐like Bi₂WO₆ nanostructures were prepared by a simple hydrothermal reaction followed by layer‐by‐layer deposition and calcination. The photocatalytic activity was evaluated using Brilliant Red X3B, an anionic azo dye, as the target organic pollutant under UV‐Vis light irradiation. The experiment results showed that the photocatalytic activity of the hybrid increases first and then decreases with increasing loading amount of TiO₂. The hybrid coated with four layers of TiO₂ (containing 20 wt‐% TiO₂) showed the highest photocatalytic activity, which is 10.45 and 3.20 times higher than that of pure Bi₂WO₆ and TiO₂, respectively. The improved photocatalytic performance of TiO₂‐modified Bi₂WO₆ nanostructures could be ascribed to the improved light‐harvesting ability, efficient photo‐generated electron‐hole separation, and enhanced adsorption of the dye. This work may shed light on the design of complex architectures and the exploitation of their potential applications.     

In situ transformation of TiO2 hierarchical nanostructures toward efficient photoelectrochemical water splitting

TiO₂ hierarchical nanomaterials have been intensively investigated as a very promising photoanode in photoelectrochemical water splitting due to its combined effects of large surface area and fast electron transfer. However, the TiO₂ hierarchical nanostructures prepared by most prevailing synthesis methods currently are at distinct disadvantages such as complicated process, poor controllability, poor interfacial contact, excessive impurities and so on. Here we report a facile route to construct a well-defined TiO₂ hierarchical nanostructure via in-situ transformation of TiO₂ nanoparticles with highly exposed {001} facets in the tube wall of the pristine TiO₂ nanotube arrays. The resulted TiO₂ hierarchical nanostructures exhibit enhanced light harvesting, lowe recombination rate of photo-generated charger carrier. Upon these synergistic effects, the target hierarchical nanostructure shows significantly improved PEC performance and excellent photo-switching response with good reproducibility and stability. Corresponding photocurrent density and photon-to-current efficiency achieve 0.76 mA cm⁻² and 0.50%, respectively, which show an enhancement of 1.70 and 1.32 times to those of the control one. This work provides a possible route for fabrication of TiO₂ starting materials with decent efficiencies.     

Anatase TiO2 spheres with high surface area and mesoporous structure via a hydrothermal process for dye-sensitized solar cells

Spherical pure anatase TiO₂ spheres with a mesoporous structure and high surface area of up to 116.5 m² g⁻¹ were prepared by a simple urea-assisted hydrothermal process and investigated as dye-sensitized solar-cell electrodes. Although the particle diameters of the prepared TiO₂ spheres ranged from 0.4 to 1.3 μm, due to the high specific surface area, mesoporous TiO₂ sphere electrode was obtained with enhanced light harvesting and a larger amount of dye loading. An overall light conversion efficiency of 7.54% under illumination of simulated AM 1.5G solar light (100 mW cm⁻²) was achieved using the mesoporous TiO₂ spheres electrode, which was significantly higher than a commercial Degussa P25 TiO₂ nanocrystals electrode (5.69%).     

Improved Efficiency of Dye‐Sensitized Solar Cells Based on a Single Layer Deposition of Skein‐Like TiO2 Nanotubes

We present a new TiO₂ morphology, featuring high surface area and open structure, synthesized by a two‐step chemical route for the manufacture of dye‐sensitized solar cells (DSSCs). This construct is sets of intertwined one‐dimensional (1D) nanostructures (i.e., nanotubes), so‐called skein‐like nanotubes (NTs). Such morphology is produced by a combination of TiC oxidation and hydrothermal processes. The mesoporous TiO₂ nanoparticles, as the product of TiC oxidation operation, is used as the precursor of hydrothermal process to grow the skein‐like NTs. The effect of processing parameters of TiC oxidation and hydrothermal processes is studied. The skein‐like morphology enables to eliminate the conventional three or fourfold layer deposition process by a single layer deposition of TiO₂ NTs. The novel TiO₂ morphology enhances photon capture of fabricated DSSC by exerting a triple function mechanism including improvement of light scattering, dye sensitization, and electron transport. The presented strategy demonstrates the feasibility of the new concept for improvement of cell efficiency by effective light management.     

TiO2–BaTiO3 nanocomposite for electron capture in dye‐sensitized solar cells

Different compositions of TiO₂–BaTiO₃ nanocomposites are synthesized with various weight ratios for dye‐sensitized solar cell (DSSC) applications. TiO₂ and BaTiO₃ nanoparticles (NPs) are synthesized by sol‐gel and solvothermal methods, respectively and are employed as the photoanode electrodes. BaTiO₃ NPs have pure cubic perovskite crystal structure with an average size of 20‐40 nm, while TiO₂ NPs show pure anatase phase with 15‐30 nm size. The power conversion efficiency (PCE) enhancement of the cells is first attained by controlling the thickness of the films for light harvesting improvement. The fabricated DSSC composed of pure BaTiO₃ NPs with an optimal thickness of 25 μm shows efficiency of 6.83%, whereas that made of pure TiO₂ NPs with 14 μm thickness has cell efficiency of 7.24%. Further improvement of cell efficiency is achieved by preparation of binary oxide nanocomposites using TiO₂ and BaTiO₃ NPs with various weight ratios. The highest PCE of 9.40% is obtained for the nanocomposite with TiO₂:BaTiO₃=85:15 (wt%). The enhancement is assigned to less recombination of photo‐generated electrons and higher incident photon to current conversion yield as a result of rapid charge collection and higher dye sensitization.     

Micron-sized silica mesh for enhancing the performance of quantum dot sensitized solar cells

Three dimensional silica mesh structures are prepared through a new and simple method for enhancing the quantum dot sensitized solar cells performance and stability.Silica patterns are made on the top of the TiO₂ photoanodes and a marked improvement in light scattering properties of meshed structures is confirmed by diffuse reflectance spectroscopy measurements. This improvement enhances the current density and consequently the cells ‘efficiency. Parameters of electron transport in cells are explored by electrochemical impedance spectroscopy (EIS). According to the EIS results, silica mesh declines the recombination rate in cells in a clear way. Here more than 50% efficiency improvement is obtained in meshed structures in comparison to cells with normal TiO₂ photoanode structures. The insulated silica mesh, reduces the electrolyte's deleterious effect on the semiconductor layers and the cells’ stability is improved.     

Fabrication of hole-patterned TiO2 photoelectrodes for solid-state dye-sensitized solar cells

We suggest a simple process to fabricate a hole-patterned TiO₂ electrode for a solid-state dye-sensitized solar cell (DSSC) to enhance cell performance through interfacial properties of the electrode with the electrolyte with minimum dye loading. The method involves prepatterning of SU-8 photoresist on a conducting glass, followed by the deposition of a nanocrystalline TiO₂ layer, calcination at 450 °C and characterization using scanning electron microscopy (SEM). Hole-patterned TiO₂ photoelectrodes yielded better solar energy conversion efficiency per dye loading compared to a conventional non-patterned photoelectrode. For example, a 50 μm hole-patterned DSSC exhibited 4.50% conversion efficiency in the solid state, which is comparable to an unpatterned flat TiO₂ photoelectrode (4.57%) however the efficiency per dye loading of the former (0.986%/g) was much greater than that of the latter (0.898%/g). The improvement was attributed to improved transmittance through the electrode as well as better interfacial properties between the electrolyte and electrode, as confirmed by UV-visible spectroscopy and electrochemical impedance (EIS) analysis.     

A study of TiO2/carbon black composition as counter electrode materials for dye-sensitized solar cells

This study describes a systematic approach of TiO₂/carbon black nanoparticles with respect to the loading amount in order to optimize the catalytic ability of triiodide reduction for dye-sensitized solar cells. In particular, the cell using an optimized TiO₂ and carbon black electrode presents an energy conversion efficiency of 7.4% with a 5:1 ratio of a 40-nm TiO₂ to carbon black. Based on the electrochemical analysis, the charge-transfer resistance of the carbon counter electrode changed based on the carbon black powder content. Electrochemical impedance spectroscopy and cyclic voltammetry study show lower resistance compared to the Pt counter electrode. The obtained nanostructures and photo electrochemical study were characterized.     

Microwave-assisted synthesis of Ag–TiO2/graphene composite for hydrogen production under visible light irradiation

Novel photocatalysts based on silver (Ag), TiO₂, and graphene were successfully synthesized by microwave-assisted hydrothermal method. The prepared photocatalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) specific surface area analysis, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The influence of silver loading and graphene incorporation on photocatalytic hydrogen (H₂) production of as-prepared samples was investigated in methanolic aqueous solution under visible light irradiation (λ≥420 nm). The results showed that Ag–TiO₂/graphene composite had appreciably enhanced photocatalytic H₂ production performance under visible light illumination compared to pure TiO₂, Ag–TiO₂ and TiO₂/graphene samples. The enhanced photocatalytic hydrogen production activity of Ag–TiO₂/graphene composite under visible light irradiation could be attributed to increased visible light absorption, reduced recombination of photogenerated charge carriers and high specific surface area. This novel study provides more insight for the development of novel visible light responsive TiO²⁻ graphene based photocatalysts for energy applications.     

Hydrothermal synthesis of pseudocubic BaTiO3 nanoparticles using TiO2 nanofibers: Study on photocatalytic and dielectric properties

In this study, TiO₂ nanofibers were fabricated via the electrospinning method followed by air annealing. Then, Ti-requirement in the conventional hydrothermal synthesis of BaTiO₃ stoichiometry was supplied by using these nanofibers. The microstructural and compositional properties of BaTiO₃ nanoparticles were studied using SEM, TEM, XRD, XPS, and Raman spectroscopy. The structural analysis showed that the cubic symmetry was the dominant one in the BaTiO₃ nanoparticles, whereas Raman spectroscopy indicated the coexistence of cubic symmetry with the tetragonal polymorph. The nanoparticles displayed higher photocatalytic reactivity under UV-A light compared to visible irradiation during decomposition of methylene blue dye and reached 24.2% and 18.8% degradation, respectively, after 1 hour. Furthermore, the dielectric properties were investigated using sintered compacts of these nanoparticles. Among the employed temperatures for sintering, the highest relative density (90%) and dielectric constant (2165 at 1 MHz) were obtained at 1250°C and 5 hours. This study revealed that the electrospun TiO₂ nanofiber precursor can successfully be used for the production of nanoscale barium titanate particles suitable for various applications.     

Construction of ternary Ag@ZnO/TiO2 fibrous membranes with hierarchical nanostructures and mechanical flexibility for water purification

Rational design of semiconductor membrane photocatalyst with good mechanical flexibility and excellent photocatalytic activity is of significance for environmental remediation. Herein, flexible Ag@ZnO/TiO₂ fibrous membranes with hierarchical nanostructures were fabricated through combining a simple electrospinning method and subsequent hydrothermal reaction and photodeposition process. In the ternary nanocomposite, ZnO nanorods were firmly anchored onto TiO₂ nanofibers, while Ag nanoparticles were evenly decorated on the surface of both ZnO and TiO₂. Benefiting from the improved light absorption, large surface area, and effective charge separation, the resultant Ag@ZnO/TiO₂ membranes displayed superior photocatalytic degradation efficiency of 91.6% toward tetracycline hydrochloride within 1 h, and also exhibited prominent antibacterial activity with a 6.5 log inactivation of E. coli after 1 h simulated solar light exposure. Significantly, the membrane photocatalyst still preserved structural integrity and mechanical flexibility after utilization. This study provides an alternative approach for designing and synthesizing flexible TiO₂-based membrane photocatalysts toward high-efficiency water purification.     

Enhancement of the photoelectric performance of dye-sensitized solar cells using Ag-doped TiO<Subscript>2</Subscript> nanofibers in a TiO<Subscript>2</Subscript> film as electrode

For high solar conversion efficiency of dye-sensitized solar cells [DSSCs], TiO₂ nanofiber [TN] and Ag-doped TiO₂ nanofiber [ATN] have been extended to be included in TiO₂ films to increase the amount of dye loading for a higher short-circuit current. The ATN was used on affected DSSCs to increase the open circuit voltage. This process had enhanced the exit in dye molecules which were rapidly split into electrons, and the DSSCs with ATN stop the recombination of the electronic process. The conversion efficiency of TiO₂ photoelectrode-based DSSCs was 4.74%; it was increased to 6.13% after adding 5 wt.% ATN into TiO₂ films. The electron lifetime of DSSCs with ATN increased from 0.29 to 0.34 s and that electron recombination was reduced.     

Mesoporous TiO<Subscript>2</Subscript> microspheres synthesized via a facile hydrothermal method for dye sensitized solar cell applications

Mesoporous TiO₂ microspheres were successfully synthesized by a facile hydrothermal process and the obtained product was sintered at 450 °C. The sintered TiO₂ powder was characterised by powder X-ray diffraction pattern and the result shows pure anatase phase with good crystalline nature. The morphological image of field emission scanning electron microscopy and high resolution transmission electron microscopy shows spherical shape and size of the particles is around 100 to 300 nm. The Brunauer–Emmett–Teller surface area of synthesized TiO₂ material was 56.32 m² g^?1 and average pore width of synthesized materials was 7.1 and 9.3 nm. Bimodal pore structure of TiO₂ microspheres has been very effective for electrolyte diffusion into photoanode in dye sensitized solar cells. The synthesized anatase TiO₂ microsphere based dye sensitized solar cells have high surface area with light scattering effect to enhance the photocurrent and conversion efficiency than the commercial P25 photoanode material. The power conversion efficiency of synthesized mesoporous TiO₂ microspheres and commercial P25 material is 4.2 and 2.7 % respectively. Therefore bimodal mesoporous anatase TiO₂ microsphere appears to be a promising and potential candidate for dye sensitized solar cells (DSSC) application.