Microstructure development of hydrothermally grown TiO2 thin films with vertically aligned nanorods

TiO₂ (rutile) thin films were deposited via a hydrothermal process by adjusting the amount of ethanol, deposition time, and temperature. Especially, various amounts of ethanol generated different degrees of supersaturation in precursor solution. It allowed us to systematically change the width, lengths, and crystallinity of a vertically aligned 1‐D nanorod structure of TiO₂ films. The oriented attachment, confirmed by scanning electron microscopy and transmission electron microscopy, was shown to be responsible for their lateral growth of TiO₂ nanorods bundled by numerous well‐oriented nanowires and their vertical growth. TiO₂ nanorod thin films were also characterized via X‐ray diffraction and UV‐Vis‐NIR spectrophotometer to find a correlation between the process conditions and nanostructural evolution. Dye sensitized solar cells were assembled to relate the nanostructures of TiO₂ films with the effectiveness of its role as a photoelectrode.     

Synthesis and characterization of TiO2 nanoparticles by using new shape controllers and its application in dye sensitized solar cells

Nanoparticulated TiO₂ materials with anatase structure were synthesized by using two step hydrothermal method and using amine ligands as shape controllers. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron spectroscopy (TEM), scanning electron microscopy (SEM), and UV–vis spectroscopy. Dye-sensitized solar cells (DSSCs) employing these materials achieved conversion efficiencies as high as 2.61% for smallest nanoparticles that was resulted of an effective shape controller.     

Surface plasmonic effect of Ag enfold ZnO pyramid nanostructured photoanode for enhanced dye sensitized solar cell application

A green approach to synthesize three dimensional pyramid structured ZnO and Ag decorated ZnO nanoparticles were developed by one pot hydrothermal method and they were successfully applied as photoanode for DSSC. Neem extract was utilized to control the size of Ag particles. The structural and morphological properties of synthesized samples of ZnO and Ag-ZnO nanocomposites have been investigated by XRD, FESEM, and HRTEM analysis respectively. The XPS studies were performed for scrutinizing the binding energy of ZnO and Ag-ZnO nanostructured materials. The UV–VIS absorption spectrum of Ag-ZnO nanostructure displaced absorption towards visible region than the pristine ZnO. The electrochemical properties of both ZnO and Ag-ZnO nanostructure were studied using EIS (Electrochemical impedance spectra). The photoconversion efficiency of Ag-ZnO based DSSC cell showed an efficiency of 3.51% which has higher conversion efficiency than pristine ZnO (2.62%).     

用于敏化太阳能电池的二氧化钛光阳极材料

敏化太阳能电池是当前清洁能源领域的研究热点之一,有望成为第三代太阳能电池。二氧化钛作为敏化太阳能电池的光阳极材料之一被广泛研究。主要综述了近20 a来二氧化钛光阳极材料的结构进展,并从电子注入效率、电子传输和基底电荷收集效率方面评述了各种结构的应用特点。另外,描述了当代三明治状二氧化钛工作电极的超薄保形覆盖层、工作层和阻挡层。然后,重点介绍了用于电子传输工作层的二氧化钛一维纳米阵列的制备方法及特点。最后,展望了光阳极结构与合成方法的未来发展趋势。     

染料敏化太阳能电池中的纳米TiO2多孔膜研究进展

介绍了染料敏化太阳能电池（DSSC）的工作原理;综述了应用于DSSC的纳米TiO2多孔膜制备方法以及掺杂改性方法。最后对用于DSSC的纳米TiO2多孔膜的发展方向进行了分析与展望。     

Immobilization of hydrothermally produced TiO2 with different phase composition for photocatalytic degradation of phenol

Hydrothermally produced TiO₂ powders with different phase composition (anatase, rutile and mixed phase) were immobilized on glass fibers and tested in the phenol mineralization process. Both H₂O₂ and O₂ were used as oxygen donors, and their performances were compared with those of the same TiO₂ samples as slurries.The catalytic properties of the immobilized different crystalline phases, rutile and anatase, show the same trend as the slurry samples: pure rutile displays the highest catalytic efficiency in the presence of H₂O₂, while samples containing anatase improve the photodegradation efficacy with O₂. It was suggested that the stability of the photogenerated electron–hole couple allows high activity of rutile in the presence of H₂O₂, while the relevant oxygen chemisorption on anatase causes high catalytic activity in the presence of O₂. A four parameters kinetics model shows that both reaction steps, the phenol degradation and the mineralization of the intermediates, are photoactivated by TiO₂.Photoactivity of the coated glass fibers is generally lower than that of slurries, even if their efficiencies are almost comparable when the oxidation is performed by H₂O₂, while much lower when the oxygen donor is O₂. As a matter of fact, the morphology of immobilized catalysts shows the presence of chestnut burr aggregates of large rutile crystalline rods on the glass fiber, which are much less compact than the aggregates of small anatase particles. This preserves rutile surface area from the coarsening effects; thus, when rutile is the more active species, as in the presence of H₂O₂, the photocatalytic activity is less affected by immobilization.     

An approach to laminated flexible Dye sensitized solar cells

We have built TiO₂ Dye sensitized solar cells (DSSCs) that combined flexible TiO₂ photoanodes coated on ITO/PET substrates with a gel electrolyte based on PVDF-HFP-SiO₂ films. Titanium isopropoxide (TiP₄) was used as additive to TiO₂ nanoparticles for increasing power conversion efficiency in Dye sensitized solar cell electrodes prepared at low-temperature (130 °C). An efficiency η_AM1.5G = 3.55% on ITO/PET substrates is obtained at 48 mW/cm² illumination with a standard liquid electrolyte based on methoxypropionitrile. Among several solvents forming gels with PVDF-HFP-SiO₂, N-methyl (pyrrolidone) (NMP) was found to enable the most stable devices. A power conversion efficiency η_AM1.5G = 2% was obtained under 10 mW/cm² with flexible TiO₂-ITO-PET photoanodes and the PVDF-HFP-SiO₂ + NMP gel electrolyte.     

Effect of TiO2 rutile nanorods on the photoelectrodes of dye-sensitized solar cells

In order to enhance the electron transport on the photoelectrodes of dye-sensitized solar cells, one-dimensional rutile nanorods were prepared using electrospun TiO₂ nanofibers. The grain size of the nanorods increased with increasing temperature. Electrochemical impedance spectroscopy measurements revealed reduced interface resistance of the cells with the one-dimensional rutile nanorods due to the improved electron transport and the enhanced electrolyte penetration. Intensity-modulated photocurrent/photovoltage spectroscopy showed that the one-dimensional rutile nanorods provided the electrons with a moving pathway and suppressed the recombination of photogenerated electrons. However, an excessive quantity of rutile nanorods created an obstacle to the electrons moving in the TiO₂ thin film. The photoelectrode with 7 wt.% rutile nanorods optimized the performance of the dye-sensitized solar cells.     

Hydrothermal Growth and Application of ZnO Nanowire Films with ZnO and TiO2 Buffer Layers in Dye-Sensitized Solar Cells

This paper reports the effects of the seed layers prepared by spin-coating and dip-coating methods on the morphology and density of ZnO nanowire arrays, thus on the performance of ZnO nanowire-based dye-sensitized solar cells (DSSCs). The nanowire films with the thick ZnO buffer layer (~0.8–1 μm thick) can improve the open circuit voltage of the DSSCs through suppressing carrier recombination, however, and cause the decrease of dye loading absorbed on ZnO nanowires. In order to further investigate the effect of TiO₂ buffer layer on the performance of ZnO nanowire-based DSSCs, compared with the ZnO nanowire-based DSSCs without a compact TiO₂ buffer layer, the photovoltaic conversion efficiency and open circuit voltage of the ZnO DSSCs with the compact TiO₂ layer (~50 nm thick) were improved by 3.9–12.5 and 2.4–41.7%, respectively. This can be attributed to the introduction of the compact TiO₂ layer prepared by sputtering method, which effectively suppressed carrier recombination occurring across both the film–electrolyte interface and the substrate–electrolyte interface.     

Dye sensitized solar cells with poly(acrylonitrile) based plasticized electrolyte containing MgI2

Polymer electrolytes can be used favorably in photo-electrochemical solar cells. A possible electrolyte for this purpose is a polyacrylonitrile-MgI₂ complex with plasticizers such as ethylene carbonate and propylene carbonate. The best ionic conductivity was obtained for samples containing 60 wt% of MgI₂ salt with respect to the weight of polyacrylonitrile, for example, at 30 °C the conductivity is 1.9 × 10⁻³ S cm⁻¹. The ionic contribution to the conductivity is dominant as shown by dc polarization tests. Furthermore, the glass transition temperature showed a minimum, −103.0 °C, for the sample with the highest conductivity indicating the importance of polymer chain flexibility for the conduction process. Measurements on a fabricated solar cell with this electrolyte exhibited an overall energy conversion efficiency of 0.84%. The short circuit current density, open circuit voltage and fill factor of the cell were 2.04 mA cm⁻², 692 mV and 59.3%, respectively.     

卟啉类有机化合物在染料敏化太阳能电池的应用研究进展

近年来,染料敏化太阳能电池(DSSC)由于低价格、易于制造成大面积、具有较宽的光谱响应范围,可接受的理论转换效率、制造工艺简单、对原料纯度要求不高、寿命长、对环境友好、应用前景广阔等优点而备受关注。染料光敏剂是DSSC的核心材料之一,其性能的优劣将对DSSC光电转化效率起着决定性的作用。介绍了DSSC的基本构造和光电原理,综述了作为光敏化剂的各种卟啉类有机化合物在染料敏化纳米晶太阳能电池中的应用。     

Effects of etching parameters on ZnO nanotubes evolved from hydrothermally synthesized ZnO nanorods

This paper reports fabrication and characterization of ZnO nanotubes on Au cylindrical spirals. Highly oriented single-crystalline ZnO nanorods were hydrothermally synthesized on Au cylindrical spirals and were etched in NaOH solution to form nanotubes. Effects of etching parameters on the lengths, wall thicknesses and morphologies of the ZnO nanotubes were studied with the etching period, etching temperature and NaOH concentration regulated respectively. It turns out that the etching parameters affect significantly the morphologies of the ZnO nanotubes but negligibly the lengths and wall thicknesses. The surfaces of the ZnO nanotube-coated Au cylindrical spirals tend to be Gaussian rough ones as the etching parameters become larger. Adjusting the etching temperature readily gives rise to perfect ZnO nanotubes. The results are beneficial for large-scale preparation of ZnO nanotubes with controllable sizes and morphologies in nanodevices.     

Enhanced efficiency in dye-sensitized solar cells based on TiO2 nanocrystal/nanotube double-layered films

A new bilayer-structured film with TiO₂ nanocrystals as underlayer and TiO₂ nanotubes as overlayer was fabricated. The resultant double-layer TiO₂ (DL-TiO₂) film could significantly improve the efficiency of dye-sensitized solar cells (DSSCs) owing to its synergic effects, i.e. effective dye adsorption mainly originated from TiO₂ nanocrystal layer and rapid electron transport in one-dimensional TiO₂ nanotube layer. The overall energy-conversion efficiency (η) of 6.15% was achieved by the formation of DL-TiO₂ film, which is 44.7% higher than that formed by pure nanocrystalline TiO₂ (NC-TiO₂) film and far larger than that formed by nanotube TiO₂ (NT-TiO₂) film (η = 0.37%). The charge recombination behavior of cells was investigated by electrochemical impedance spectra, and the results showed that DL-TiO₂ film-based cell possessed the lowest transfer resistance and the longest electron lifetime. The incident-photon-to-current efficiency spectra indicated that the broad bands covered almost the entire visible spectrum from 400 to 700 nm with the maxima of 57.3%, 40.3%, and 2.2% at a wavelength of ∼530 nm for DL-TiO₂-, NC-TiO₂-, and NT-TiO₂-based solar cells, respectively. It is expected that the double-layer film electrode can be extended to other composite films with different layer structures and morphologies for enhancing the efficiencies of DSSCs.     

The photovoltaic efficiencies on dye sensitized solar cells assembled with nanoporous carbon/TiO2 composites

This study examined the characterization of nanoporous structured carbon/TiO₂ composites and its application to dye-sensitized solar cells. TEM of nanoporous structured carbon revealed nanopore sizes of 2.0–3.0 nm with a regular hexagonal form. When nanoporous structured carbon was mixed to TiO₂ particles and then was applied to DSSC, the energy conversion efficiency was enhanced considerably compared with that using only nanometer sized pure TiO₂: the energy conversion efficiency of the DSSC prepared from nanoporous carbon/TiO₂ composites was approximately 3.38%, compared to 2.49% using pure TiO₂. We confirmed from FT-IR spectroscopy that the dye molecules were attached perfectly to the surface and more was absorbed on the nanoporous structured carbon/TiO₂ composite than on the pure TiO₂ particles. In impedance measurements, R₃ which means the Nernstian diffusion within the electrolytes was largely decreased in a cell assembled by nanoporous carbon/TiO₂ composites than that of TiO₂.     

Exposed crystal surface-controlled rutile TiO2 nanorods prepared by hydrothermal treatment in the presence of poly(vinyl pyrrolidone)

Rutile TiO₂ particles with specific exposed crystal faces were prepared by hydrothermal treatment of titanium trichloride (TiCl₃) solution with poly(vinyl pyrrolidone) (PVP) as a shape-control reagent. Crystal phase, shape, and size of TiO₂ particles were found to be greatly dependent on the concentration of PVP in the solution. The exposed crystal surface of TiO₂ was controlled by changing the concentration of PVP in TiCl₃ and NaCl solutions. The prepared TiO₂ particles were characterized by TEM, SEM, XRD, and specific surface area measurements. The photocatalytic activity of the synthesized TiO₂ particles was evaluated by decomposition of acetaldehyde and toluene in gas phase. The synthesized TiO₂ particles showed higher photocatalytic activity for degradation of acetaldehyde and toluene than did commercial TiO₂ particles (MT-600B). However, the tendency of photocatalytic activities of the synthesized TiO₂ particles for degradation of acetaldehyde in gas phase was different from that for degradation of toluene. From the photodeposition of Pt and PbO₂, we propose that the (1 1 0) face provides reductive sites and that the (1 1 1) face provides oxidative sites. The results suggest that the crystal faces facilitate the separation of electrons and holes, resulting in improvement in photocatalytic activity.     

CdS quantum dot-sensitized solar cells based on nano-branched TiO2 arrays

Nano-branched rutile TiO₂ nanorod arrays were grown on F:SnO₂ conductive glass (FTO) by a facile, two-step wet chemical synthesis process at low temperature. The length of the nanobranches was tailored by controlling the growth time, after which CdS quantum dots were deposited on the nano-branched TiO₂ arrays using the successive ionic layer adsorption and reaction method to make a photoanode for quantum dot-sensitized solar cells (QDSCs). The photovoltaic properties of the CdS-sensitized nano-branched TiO₂ solar cells were studied systematically. A short-circuit current intensity of approximately 7 mA/cm² and a light-to-electricity conversion efficiency of 0.95% were recorded for cells based on optimized nano-branched TiO₂ arrays, indicating an increase of 138% compared to those based on unbranched TiO₂ nanorod arrays. The improved performance is attributed to a markedly enlarged surface area provided by the nanobranches and better electron conductivity in the one-dimensional, well-aligned TiO₂ nanorod trunks.     

Eosin-Y and N3-Dye sensitized solar cells (DSSCs) based on novel nanocoral TiO2: A comparative study

Titanium oxide (TiO₂) nanocorals containing nanopolyps have been synthesized by a cost effective hydrothermal route directly on fluorine doped tin oxide (FTO) coated conducting glass substrates. The morphological features and physical properties of TiO₂ films were investigated by field-emission scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, Fourier transform Raman spectroscopy, room temperature photoluminescence spectroscopy and X-ray photoelectron spectroscopy. The surface morphology revealed the formation of TiO₂ corals having nanosized (30–40 nm) polyps. Further, we have studied its dye sensitized solar cell performance by using Eosin-Y and N3-Dye. The results indicate that the photoconversion efficiency of N3-Dye is 66% compared to that of Eosin-Y. The highest solar energy conversion efficiency of 2.37% was observed for N3-Dye loaded DSSCs.     

Hydrothermally grown uniform TiO2 coatings on ZrO2 fibers and their infrared reflective and thermal conductive properties

Improving the infrared reflectivity of ZrO₂ polycrystalline fibers is of great benefit to its thermal applications. In the present research, we cast a highly uniform TiO₂ coating with a thickness ranging from dozens to hundreds of nanometers on ZrO₂ fibers by utilizing hydrothermal growth. The coating bonds tightly to the ZrO₂ fibers via Zr–O–Ti chemical linkages, and the thickness of the coating can be tailored by varying the hydrothermal growth time. The TiO₂ coating, acting as a sheath towards electromagnetic radiation, not only reflected light with wavelengths ranging from the visible region to the infrared region and up to 8 μm but also shielded the Raman signals of the ZrO₂ fibers. The present research provides an efficient way to cast controllable and uniform coatings on flexible fiber materials. The obtained ZrO₂ fibers coated with TiO₂ may have applications such as reinforcement for bulk ceramics, thermal barrier coatings, aerogels, etc., thus performing the dual functions of mechanical strengthening and thermal insulation.     

Structural,morphological, and optical studies of hydrothermally synthesized Nb-added TiO2 for DSSC application

Herein, titanium dioxide (TiO₂) nanoparticles doped with various concentrations (0–7 wt %) of niobium (Nb) are hydrothermally synthesized and used effectively as a photoelectrode for application in dye-sensitized solar cells (DSSCs). The rutile-to-anatase phase transition, accompanied by a change in crystallite size from 23.75 to 9.77 nm, is confirmed via X-ray diffraction (XRD) and Fourier transform (FT)-Raman spectroscopy. In addition, the prepared Nb–TiO₂ nanoparticles exhibit a spherical morphology with a mean grain diameter of 43.38–50.69 nm. Further, X-ray photoelectron spectroscopy (XPS) indicates a shift in the Fermi level of the TiO₂ towards the conduction band minimum, and an increase in the bandgap from 2.69 to 2.88 eV, with increasing Nb concentration. The resulting increases in the short-circuit current density (J_SC) and open circuit voltage (V_OC) with the increased injection and conductivity of electrons lead to the enhancement of the DSSC performance. EIS measurements represents the effect of Nb doping on charge transporting and recombination behavior of DSSCs. Moreover, the Nb–TiO₂-based DSSCs provide a better power conversion performance as compared to that of the pristine TiO₂.     

Investigating photocatalytic property of TiO2 nanorods fabricated hydrothermally at equal molar ratio of KOH and NaOH

TiO₂ photocatalysts were prepared by hydrothermal method at temperatures of 110, 155, and 200°C for 24 hours, using KOH (5 mol/L):NaOH (5 mol/L) solution and anatase TiO₂ powder with an average particle size of 0.13 μm as precursor and by calcining at two different temperatures of 450 and 700°C. An overall photocatalytic removal efficiency of 93% was achieved for Rhodamine B dye under UV light irradiation by the photocatalyst obtained at synthesis and calcination temperatures of 155 and 700°C, respectively, which indicated a nanorod morphology with a mean diameter of about 34 nm.