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%.     

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.     

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.     

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.     

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.     

The effects of the thickness of TiO2 films on the performance of dye-sensitized solar cells

Nanocrystalline anatase TiO₂ thin films with different thicknesses (0.5-2.0 μm) have been deposited on ITO-coated glass substrates by a sol-gel method and rapid thermal annealing for application as the work electrode for dye-sensitized solar cells (DSSC). From the results, the increases in thickness of TiO₂ films can increase adsorption of the N3 dye through TiO₂ layers to improve the short-circuit photocurrent (J_sc) and open-circuit voltage (V_oc), respectively. However, the J_sc and V_oc of DSSC with a TiO₂ film thickness of 2.0 μm (8.5 mA/cm² and 0.61 V) are smaller than those of DSSC with a TiO₂ film thickness of 1.5 μm (9.2 mA/cm² and 0.62 V). It could be due to the fact that the increased thickness of TiO₂ thin films also resulted in a decrease in the transmittance of TiO₂ thin films thus reducing the incident light intensity on the N3 dye. An optimum power conversion efficiency (η) of 2.9% was obtained in a DSSC with the TiO₂ film thickness of 1.5 μm.     

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.     

Improved performance of dye-sensitized solar cells with laser-textured nanoporous TiO2 photoanodes

This study reports the improved performance of dye-sensitized solar cells (DSSCs) with TiO₂ photoanodes textured by a KrF excimer laser. The excimer laser was employed to create texture for the photoanodes after sintering from TiO₂ pastes at 510 °C. The results revealed that the efficiency increased by 24% (from 4.49% to 5.59%) for cells with photoanodes annealed with 11,200 shots of 80 mJ/cm² laser irradiation. The porous TiO₂ photoanodes became less transparent after the laser treatment, indicating an increase in light trapping due to a rougher texture. A notable enhancement of light absorption for wavelengths greater than 550 nm was achieved. The open circuit voltage (V_oc) and fill factor (FF) were also improved. The surface re-melting and solidification process may change the series and shunt resistances and reduce the surface recombination centers, leading to the increases of V_oc and FF.     

Surface treatment of TiO2 films for dye-sensitized solar cells using atmospheric-pressure non-equilibrium DC pulse discharge plasma jet

In this paper, we report the utilization of the DC pulse discharge plasma jet technique as a means for the preparation of titanium oxide (TiO₂) films on fluorine dope tin oxide (FTO) coated glass substrates used for dye-sensitized solar cells (DSCs). The TiO₂ film 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 by the TiO₂ film exhibited an energy conversion efficiency of 5.7% at 100 mW/cm² light intensity. Consequently, we believe that the optimization between the specific surface area and photocurrent density of TiO₂ film was achieved by the plasma surface treatment which also contributed to the improvement of energy conversion efficiency of DSCs.     

DNA-like dye-sensitized solar cells based on TiO2 nanowire-covered nanotube bilayer film electrodes

This paper reports a two-step formation of a TiO₂ nanowire-covered nanotube bilayer film technique and its application in DNA-like dye-sensitized solar cells. The bilayer film was prepared by the electrochemical anodization first and then the hydrothermal method. From the reflectivity spectrum and scanning electron microscopy it is observed that the nanowire layer on the top cannot only decrease the reflectivity of the film, but also play a role to modify the film cracks. Compared with the dye-sensitized solar cells based on a single layer electrode, the cell with the bilayer film showed higher photovoltaic parameters and a lower dark current, which is due to its higher light harvesting efficiency and lower charge recombination between the electrolyte and the substrates.     

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.     

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.     

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.     

The role of the TiO2 nanotube array morphologies in the dye-sensitized solar cells

Arrays of TiO₂ nanotubes were fabricated by the anodization of Ti foils and then used in assembling dye-sensitized solar cells (DSSCs). The role of the morphologies of the TiO₂ nanotubes in the photovoltaic performances of the DSSCs was studied in terms of the surface topography and the tube length. The necessity of removing the nanoporous films from the surface of the nanotube arrays for good DSSC performance has been demonstrated. Also, it has been shown that appropriately increasing the tube length was an effective measure for enhancing both the short-circuit current density and the conversion efficiency of the DSSCs.     

TiO2 pore-filling and its effect on the efficiency of solid-state dye-sensitized solar cells

Solid-state dye-sensitized solar cells have been the focus of much attention over the past few years. We have recently been able to demonstrate efficiencies in excess of 4% and further improvements are expected. Here we compare a range of different hole conductor materials and investigate a number of key parameters which affect their performance. Wetting and pore-filling of the nanoporous TiO₂ layer by the hole transporter appears to play a critical role in determining the final efficiency of the cell. A comparison of our results shows the importance of complete filling in contrast to just wetting of the nanoporous TiO₂ layer, which is generally underestimated.     

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%.     

Modified multistep electrophoretic deposition of TiO2 nanoparticles to prepare high quality thin films for dye-sensitized solar cell

In this study, a modified procedure is introduced which consists of multistep process for improving the structure of mesoporous TiO₂ films. The films were prepared by electrophoretic deposition (EPD) on FTO (F-SnO₂ coated glass). It is shown that high quality TiO₂ film can be produced by multistep EPD method. The effect of EPD time on the thickness and density of the films have been investigated. The performance of dye-sensitized solar cells (DSSCs) that were fabricated by improved layer are tested under AM 1.5 simulated sunlight. Finally, the structure and effective parameters of DSSCs that were fabricated by one step and multistep EPD are investigated precisely, using electrochemical impedance spectroscopy.     

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.     

Preparation and antibacterial behavior of Fe-doped nanostructured TiO2 thin films

Fe³⁺-doped nanostructured TiO₂ thin films with antibacterial activity were prepared on soda–lime–silica glass slides by using sol–gel technology. Water containing Escherichia coli K-12 with TiO₂ thin films in was exposed to low intensity fluorescent light and antibacterial efficiency was evaluated with spread plate techniques. The films are porous and have anatase phase. Iron ions increased luminous energy utilization as the absorption edge of the Fe³⁺-doped film has a red shift compared to that of the pure TiO₂ film in the UV–VIS absorption spectrum. The bacterial removal efficiency reached 95% at the optimum concentration of iron ion (about 0.5% (mol)) after 120 min irradiation. The antibacterial behavior of the doped TiO₂ films was explicitly observed using scanning electron microscopy and cell wall damage was found.