A simple electrophoretic deposition method to prepare TiO2-B nanoribbon thin films for dye-sensitized solar cells

This paper describes a simple method utilizing electrophoretic deposition (EPD) to quickly synthesize hydrogen titanate nanoribbon films. The subsequent heating of the hydrogen titanate nanoribbon films causes the dehydration of interlayered OH groups, thereby leading to TiO₂-B nanoribbon films. Thick, uniform TiO₂-B nanoribbon films were obtained from prepared alkali suspensions. The crystal structure of the hydrogen titanate and TiO₂-B nanoribbon films obtained from EPD underwent analysis by X-ray diffraction and high-resolution transmission electron microscope. EPD controlled the thickness of TiO₂-B nanoribbons films. TiO₂-B-coated fluorine-doped tin oxide films were dye-sensitized with N3 and used as a photoanode in an electrochemical solar cell. The solar cell yielded conversion efficiencies of 0.87% for an incident solar energy of 100 mW/cm².     

Multi-layered TiO2 nanostructured films for dye-sensitized solar cells

Multi-layered TiO₂ nanostructured films were fabricated to improve the light harvest efficiency of the dye-adsorbed TiO₂ electrode in dye-sensitized solar cells (DSSCs) by light scattering. Three different structures of TiO₂ electrodes, with layers consisting of TiO₂ pastes with average diameters of 9, 20, and 300 nm, respectively, were fabricated and their photovoltaic effects on the DSSC devices were investigated. By utilizing the multi-layered TiO₂ electrode constructed using the three different TiO₂ pastes, the overall power conversion efficiency of the DSSC devices in the PEG-based electrolyte was increased to 5.24% under irradiation of 100 mW/cm² at AM 1.5.     

TiO2 coated SnO2 nanosheet films for dye-sensitized solar cells

TiO₂-coated SnO₂ nanosheet (TiO₂-SnO₂ NS) films about 300 nm in thickness were fabricated on fluorine-doped tin oxide glass by a two-step process with facile solution-grown approach and subsequent hydrolysis of TiCl₄ aqueous solution. The as-prepared TiO₂-SnO₂ NSs were characterized by scanning electron microscopy and X-ray diffraction. The performances of the dye-sensitized solar cells (DSCs) with TiO₂-SnO₂ NSs were analyzed by current-voltage measurements and electrochemical impedance spectroscopy. Experimental results show that the introduction of TiO₂-SnO₂ NSs can provide an efficient electron transition channel along the SnO₂ nanosheets, increase the short current density, and finally improve the conversion efficiency for the DSCs from 4.52 to 5.71%.     

Low-temperature deposition of crystallized TiO2 thin films

Crystallized TiO₂ thin films were deposited on a non-heated substrate by two methods: oxygen-ion-assisted reactive evaporation (ORE) and high-rate reactive sputtering (HRS) using two sputtering sources. When the films were deposited on an unheated glass substrate, amorphous films were initially grown on the substrate in case of both deposition methods, although an increase in oxygen-ion energy above 600 eV led to a growth of a crystallized layer on the amorphous films in the case of ORE. When the films were deposited by HRS on a crystallized TiO₂ seed layer, homo-epitaxial growth was observed, and crystallized TiO₂ films with an excellent hydrophilic property were obtained on unheated substrate. In contrast, when the films were deposited by ORE, amorphous films were initially grown on the crystallized TiO₂ seed layer in a similar manner to the deposition of films on a glass substrate, and homo-epitaxial growth was not observed. These results suggest that the large kinetic energy of titanium atoms arriving at the substrate during HRS is a key factor in promoting epitaxial growth of the TiO₂ film at low temperature.     

色素增感太阳电池多孔TiO2薄膜研究

采用溶胶-凝胶法制备复合硫化镉的二氧化钛纳米多孔薄膜;用差热分析仪、X射线分析仪、紫外-可见光分光光度计对薄膜的热处理制度、吸光度以及电池的性能进行了研究.结果表明在550℃下热处理,可以形成结晶良好,吸光度较好的TiO2薄膜;试制了太阳能电池,测定了电池性能.     

Sputter deposition and surface treatment of TiO2 films for dye-sensitized solar cells using reactive RF plasma

Sputter deposition followed by surface treatment was studied using reactive RF plasma as a method for preparing titanium oxide (TiO₂) films on indium tin oxide (ITO) coated glass substrate for dye-sensitized solar cells (DSCs). Anatase structure TiO₂ films deposited by reactive RF magnetron sputtering under the conditions of Ar/O₂(5%) mixtures, RF power of 600 W and substrate temperature of 400 °C were surface-treated by inductive coupled plasma (ICP) with Ar/O₂ mixtures at substrate temperature of 400 °C, and thus the films were applied to the DSCs. The TiO₂ films made on these experimental bases exhibited the BET specific surface area of 95 m²/g, the pore volume of 0.3 cm²/g and the TEM particle size of ∼ 25 nm. The DSCs made of this TiO₂ material exhibited an energy conversion efficiency of about 2.25% at 100 mW/cm² light intensity.     

Preparation of anatase TiO2 thin films for dye-sensitized solar cells by DC reactive magnetron sputtering technique

Anatase titanium dioxide (TiO₂) thin films are prepared by DC reactive magnetron sputtering using Ti target as the source material. In this work argon and oxygen are used as sputtering and reactive gas respectively. DC power is used at 100 W per 1 h. The distance between the target and substrate is fixed at 4 cm. The glass substrate temperature value varies from room temperature to 400 °C. The crystalline structure of the films is determined by X-ray diffraction analysis. All the films deposited at temperatures lower than 300 °C were amorphous, whereas films obtained at higher temperature grew in crystalline anatase phase. Phase transition from amorphous to anatase is observed at 400 °C annealing temperature. Transmittances of the TiO₂ thin films were measured using UV-visible NIR spectrophotometer. The direct and indirect optical band gap for room temperature and substrate temperature at 400 °C is found to be 3.50, 3.41 eV and 3.50, 3.54 eV respectively. The transmittance of TiO₂ thin films is noted higher than 75%. A comparison among all the films obtained at room temperature showed a transmittance value higher for films obtained at substrate temperature of 400 °C. The morphology of the films and the identification of the surface chemical stoichiometry of the deposited film at 400 °C were studied respectively, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The surface roughness and the grain size are measured using AFM.     

Templated synthesis of ordered porous TiO2 films and their application in dye-sensitized solar cell

Ordered porous TiO₂ thin films were fabricated on conductive glass by using colloid crystal template of polystyrene (PS) spheres. Microstructural characterization by scanning electron microscopy techniques was carried out to explore the porous structural changes due to the PS templates which could be controlled by adjusting the drawing rate. Photovoltaic performance was measured and this revealed the effect of microstructural changes. The results showed that monolayer porous TiO₂ films and multilayer porous TiO₂ films could be successfully prepared. And multilayer porous TiO₂ films provided large surface area for dye absorption to increase the efficiency of dye-sensitized solar cells (DSSCs) which were assembled by porous TiO₂ films.     

Hybrid photoelectrode by using vertically aligned rutile TiO2 nanowires inlaid with anatase TiO2 nanoparticles for dye-sensitized solar cells

We report a hybrid photoelectrode fabricated by using single crystalline rutile TiO₂ nanowires (NWs) inlaid with anatase TiO₂ nanoparticles (NPs) for efficient dye-sensitized solar cells. For this purpose, ∼4-μm-thick vertically aligned NWs were synthesized on the FTO glass substrate through a solvothermal treatment. Then, as-prepared NW film was treated with the NP colloidal dispersion to construct the NW–NP film. In particular, the NWs offer a fast pathway for electron transport as well as light scattering effect. On the other hand, the inlaid NPs give an extra amount of space for the dye-uptake. Accordingly, the present NW–NP electrode exhibited 6.2% of the conversion efficiency, which corresponds to ∼48% improvement over the efficiency of the NP-DSC. We attribute this notable result to the synergetic effects of the enhanced light confinement, charge collection, and dye-loading.     

Plasma-enhanced chemical vapor deposition of TiO2 thin films for dielectric applications

Amorphous TiO₂ thin films were formed by plasma-enhanced chemical vapor deposition (PECVD) from mixtures of titanium IV isopropoxide (Ti(O-i-C₃H₇)₄) and oxygen. The deposition rate was found to be weakly activated, with an apparent activation energy of 4.5 kJ/mol. The deposition rate increased with equivalence ratio and decreased with plasma power. This dependence on atomic oxygen density was consistent with behavior observed in other metal oxide PECVD systems. Metal-insulator-silicon devices were fabricated, and characterized using capacitance-voltage measurements. The apparent dielectric constant of the TiO₂ thin films increased from 15 to 82 with film thickness. The observed variations were consistent with the formation of an interfacial SiO₂ layer. Assuming that a TiO₂/SiO₂ bilayer behaves as two capacitors in series, an intrinsic TiO₂ dielectric constant of 82 ± 10 and an interfacial SiO₂ layer thickness of 3 ± 1 nm were extracted from electrical measurements.     

TiO2 thin films for dyes photodegradation

The aim of the present study is to investigate the influence of the TiO₂ specific surface (powder, film) on the photocatalytic degradation of methyl orange. Porous TiO₂ films were deposited on transparent conducting oxide substrates by spray pyrolysis deposition. The films were characterized by X-ray diffraction (XRD), Scanning Electronic Microscopy, and the UV-Vis spectroscopy. The XRD spectra of nanoporous TiO₂ films revealed an anatase, crystalline structure that is known as the most suitable structure in photocatalysis. The average thickness of the films was 260 nm and the measured band gap is 3.44 eV. The influence of the operational parameters (dye concentration, contact time) on the degradation rate of the dye on TiO₂ was examined. There were calculated the kinetic parameters and the process efficiency. Using thin films of TiO₂ is technologically recommended but raises problems due to lowering the amount of catalyst available for the dye degradation.     

Charge recombination reduction in dye-sensitized solar cells by depositing ultrapure TiO2 nanoparticles on “inert” BaTiO3 films

Ultrapure TiO₂ nanoparticles (∼5 nm in size) were supported on “inert” BaTiO₃ films by TiCl₄ treatment, which was used to fabricate dye-sensitized solar cells (DSSCs). The optimized electrode, designated as BaTiO₃/TiO₂(4), was obtained upon four cycles of TiCl₄ treatment. DSSC with BaTiO₃/TiO₂(4) electrode exhibits superior power conversion efficiency (PCE) compared to that with conventional anatase TiO₂ (∼25 nm in size) electrode. The interfacial charge recombination kinetics was investigated by electrochemical impedance spectroscopy (EIS) and intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS). In contrast to DSSC with anatase TiO₂ electrode, the dramatically enhanced electron lifetime for DSSC with BaTiO₃/TiO₂(4) electrode could be attributed to the decrease of recombination reaction at the TiO₂ photoelectrode/electrolyte interface. It is proposed that the lower interfacial charge recombination can be related to the relatively shallower trap distributions in DSSC with BaTiO₃/TiO₂(4) electrode.     

Double-layered TiO2 cavity/nanoparticle photoelectrodes for efficient dye-sensitized solar cells

TiO₂ nanoparticles (NPs) in the size of ~25 nm, namely P25, are very common material as the electron collecting layer in dye-sensitized solar cells (DSSCs). However, the light-scattering improvement of TiO₂ NP photoelectrodes is still a challenge. Here, we built TiO₂ cavities on the top of the TiO₂ NP layer by using carbonaceous microspheres as the template, forming the TiO₂ cavity/nanoparticle (C/NP) photoelectrode for the application in DSSCs. The cavity amount in the TiO₂ C/NP photoelectrode was controlled by adjusting the weight ratio of carbonaceous microspheres. SEM results confirm the successful formation of the double-layered TiO₂ C/NP electrode. J‒V tests show that the optimized TiO₂ C/NP electrode prepared with 25 wt.% carbonaceous microspheres contributes to remarkable improvement of the short-circuit current density (J_sc) and the power conversion efficiency (PCE). The best photovoltaic performance solar cell with the PCE of 9.08% is achieved with the optimized TiO₂ C/NP photoelectrode, which is over 98% higher than that of the TiO₂ NP photoelectrode. Further investigations of UV-vis DRS, IPCE, OCVD, and EIS demonstrate that the competition between light scattering effect and charges recombination in this TiO₂ C/NP photoelectrode is responsible for the PCE enhancement.     

Templated synthesis of porous TiO2 thin films using amphiphilic graft copolymer and their use in dye-sensitized solar cells

Porous TiO₂ thin films have been prepared using an amphiphilic graft copolymer, i.e. poly(vinylidene fluoride-co-chlorotrifluoroethylene)-graft-poly(oxyethylene methacrylate) (P(VDF-co-CTFE)-g-POEM) as a structure-directing agent via the sol-gel process. The graft copolymer was synthesized via atom transfer radical polymerization using CTFE units as an initiating site and designed to have a hydrophobic P(VDF-co-CTFE) domain and a hydrophilic POEM domain. Fourier transform-infra red spectroscopy indicated that a hydrophilic titania precursor was selectively incorporated into hydrophilic POEM domains. In-situ formation and morphologies of porous TiO₂ thin films were confirmed by ultraviolet-visible spectroscopy, X-ray diffraction, transmission electron microscopy and thermogravimetric analysis. The resultant porous TiO₂ films with 10-25 nm in size were used as a photoelectrode for solid-state dye-sensitized solar cells, exhibiting energy conversion efficiency of 2.8% at 100 mW/cm².     

Effects of HNO3 treatment of TiO2 nanoparticles on the photovoltaic properties of dye-sensitized solar cells

The effects of the nitric acid (HNO₃) treatment of TiO₂ nanoparticles on the photovoltaic properties of the dye-sensitized solar cell (DSSC) were investigated. The HNO₃ treatment enhanced the dispersion of TiO₂ particles, increased the surface area and porosity of the sintered TiO₂ films, increased the relative proportion of the Ti³⁺ state in the Ti 2p X-ray photoelectron spectroscopy spectrum, significantly increased the amount of adsorbed dye molecules on the TiO₂ electrode, and reduced the charge-transfer resistance at the TiO₂/dye/electrolyte interface. The short circuit photocurrent density (I_sc) was increased due to the increased amount of adsorbed dye molecules and the reduced charge-transfer resistance. The HNO₃ pre-treatment of TiO₂ particles improved the overall conversion efficiency of the DSSC by about 14%.     

Electrolytic and electrophoretic deposition of CeO2 films

Cerium oxide films of thickness 0.1–300 μm were deposited on Ni substrates via cathodic electrolytic and electrophoretic deposition. The films were studied by X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. Experimental results obtained by both deposition methods are compared. The influence of deposition parameters and additives on deposition yields and film morphologies is studied and discussed.     

Enhancing efficiency of dye-sensitized solar cells by combining use of TiO2 nanotubes and nanoparticles

Titanium dioxide nanotubes (TiNTs) were fabricated from commercial P25 TiO₂ powders via alkali hydrothermal transformation. Dye-sensitized solar cells (DSCs) were constructed by application of TiNTs and P25 nanoparticles with various weight percentages. The influence of the TiNT concentration on the performance of DSCs was investigated systematically. The electrochemical impedance spectroscopy (EIS) technique was employed to quantify the recombination resistance, electron lifetime and time constant in DSCs both under illumination and in the dark. The DSC based on TiNT/P25 hybrids showed a better photovoltaic performance than the cell purely made of TiO₂ nanoparticles. The open-voltage (V_oc), fill factor (FF) and efficiency (η) continuously increased with the TiO₂ nanotube concentration from 0 to 50 wt%, which was correlated with the suppression of the electron recombination as found out from EIS studies. Respectable photovoltaic performance of ca. 7.41% under the light intensity of 100 mW cm⁻² (AM 1.5G) was achieved for DSCs using 90 wt% TiO₂ nanotubes incorporated in TiO₂ electrodes.     

New approach for generating Cu2O/TiO2 composite films for solar cell applications

In this paper, Cu₂O was studied as a photon absorber for solar cell applications. Cu₂O was deposited on a TiO₂ film using the electrochemical deposition (ECD) method. Based on the physical appearance of the samples, the particles of Cu₂O seemed to penetrate the TiO₂ film and were primarily deposited near the TiO₂/substrate interface rather than on the TiO₂ film surface. This method could be one way to generate a p-n bulk-heterojunction interface. The film was confirmed to be a Cu₂O/TiO₂ composite via X-ray diffraction measurements. The top electrode was formed by evaporating indium for I-V characterization, and the fabricated cell showed photovoltaic properties.     

Dopamine/TiO2 hybrid thin films prepared by the liquid phase deposition method

Liquid phase deposition method is applied to one-step production of a hybrid material composed by dopamine(DA) and TiO₂ anatase. An optimized amount of the enediol derivative is added to a fluoride titania precursor aqueous solution in order to entrap this modifier within the growing TiO₂, yielding a DA/TiO₂ nanocomposite material. Uniform, well-adhered and brown-colored thin films are deposited on indium tin oxide covered glass substrate. The DA/TiO₂ hybrid material has been characterized by infrared spectroscopy, electronic microscopy, X-ray diffraction and UV-vis spectroscopy. The formation of the hybrid material seems to be reasonably explained by linkage of different TiO₂ nanocrystallites taking advantage of both enediol and amine groups of DA.     

Hydrophilicity of anatase TiO2/Cr-doped TiO2 thin films with different band gaps

Based on the concept that the electron-hole separation effect caused by a different band-gap structure would improve its hydrophilicity, anatase-TiO₂/Cr-doped TiO₂ thin films were synthesized by DC magnetron sputtering. The optical band gaps of TiO₂ thin films decreased from 3.23 to 2.95 eV with increasing Cr-doping content. Multilayer TiO₂ thin films with different band gaps exhibited a superhydrophilicity under UV illumination. In particular, in anatase TiO₂ (3.23 eV)/4.8% Cr-doped TiO₂ (2.95 eV), the hydrophilicity, which indicated a contact angle of less than 20°, lasted for 48 h in the dark after UV illumination was discontinued. This outstanding result has rarely been reported for TiO₂ thin films, which confirmed that the prominent superhydrophilicity of anatase TiO₂/Cr-doped TiO₂/glass could be attributed to the retardation of electron-hole recombination caused by the band-gap difference.