Fabrication and characterization of photoelectrode thin films with different morphologies of TiO2 nanoparticles for dye-sensitized solar cells

This study deals with the fabrication of three different morphologies of TiO2 nanoparticles to fabricate two-layer photoelectrode thin film for dye-sensitized solar cells (DSSC). The four different TiO2 morphologies are titania nanotubes (Tnt), TiO2 nanoparticles (H220), TiO2 nanoparticle (SP) and commercial DP-25 nanoparticles (P-25). To prepare the thin films of the photoelectrodes, the first layer is coated by H220 TiO2 nanoparticles, and the second is coated by 3 kinds of materials optimally proportionally mixed - P25, SP and Tnt. The photoelectric conversion efficiency of DSSCs with photoelectrodes fabricated using H220 reached 6.31%. Finally, the TiO2 nanaomaterials with four different morphologies were used to prepare a two layer photoelectrode with the structure of H220/P25-Tnt-SP which was combined with a Pt counter electrode to assemble DSSCs. These DSSCs had photoelectric conversion efficiencies of as high as 7.47%.     

Dry-spray deposition of TiO2 for a flexible dye-sensitized solar cell (DSSC) using a nanoparticle deposition system (NPDS)

TiO2 powders were deposited on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates for application to the photoelectrode of a dye-sensitized solar cell (DSSC). In the conventional DSSC manufacturing process, a semiconductor oxide such as TiO2 powder requires a sintering process at higher temperature than the glass transition temperature (T(g)) of polymers, and thus utilization of flexible polymer substrates in DSSC research has been constrained. To overcome this restriction related to sintering, we used a nanoparticle deposition system (NPDS) that could produce a thin coating layer through a dry-spray method under atmospheric pressure at room temperature. The powder was sprayed through a slit-type nozzle having a 0.4 x 10 mm2 rectangular outlet. In order to determine the deposited TiO2 thickness, five kinds of TiO2 layered specimens were prepared, where the specimens have single and double layer structures. Deposited powders on the ITO coated PET substrates were observed using FE-SEM and a scan profiler The thicker TiO2 photoelectrode with a DSSC having a double layer structure showed higher energy efficiency than the single layer case. The highest fabricated flexible DSSC displayed a short circuit current density J(sc) = 1.99 mA cm(-2), open circuit voltage V(oc) = 0.71 V, and energy efficiency eta = 0.94%. These results demonstrate the possibility of utilizing the dry-spray method to fabricate a TiO2 layer on flexible polymer substrates at room temperature under atmospheric pressure.     

Effect of MWCNT Inclusion in TiO2 Nanowire Array Film on the Photoelectrochemical Performance

Rutile TiO2 nanowire array films with multi-walled carbon nanotube(MWCNT) inclusion perpendicularly grown on fluorine-doped tin oxide(FTO) substrate were prepared by a facile hydrothermal method.The absorption edges of the TiO2 nanowire array films are blue-shifted with increasing MWCNT content.The resistance of the TiO2 nanowire array film is decreased by MWCNT inclusion.The optimum TiO2 /MWCNT molar ratio in the feedstock is 1:0.1.For the TiO2 nanowire array film with MWCNT inclusion served as electrode in dye-sensitized solar cell(DSSC),an overall 194% increase of photoelectric conversion efficiency has been achieved.     

Enhanced electron lifetime on nitrogen-doped TiO2 films for dye-sensitized solar cells

Nitrogen-doped TiO2 crystallites were prepared via the hydrolysis of TiCl4 using an ammonia medium in an aqueous solution for DSSC photoelectrodes. The optimized photoelectrode for the DSSC was prepared with 9.4 nm sized N-doped TiO2 crystal (BET; 200 m2/g), which provides a relatively high short circuit current and energy conversion efficiency in the DSSC. The photovoltaic performance of the N-doped TiO2 electrode was confirmed using incident photon-to-current efficient spectra, impedance analyses, and Bode-phase plots which proved that the N-doped TiO2 electrode has a significantly enhanced electron lifetime compared with that of the P25 electrode.     

Enhanced performance of TiO2 nanoparticle and aerogel composite electrode for dye sensitized solar cell

To evaluate the effects of specific surface area to the photocurrent conversion efficiency of dye-sensitized solar cell (DSC), we adopted TiO2 aerogel (TA)/nanoparticle (TP) composite as a photoelectrode. We prepared three types of photoelectrodes, TPs, TAs, and TATPs (1:1 TAs and TPs composite photoelectrode). The performance of TATP composite electrode was compared with that of TP and TAs. TATPs showed the improved cell efficiency, more than 0.5%, compared with a reference TPs below 15 micrometer thickness. Although the introduction of TAs increases the specific surface area for the dye adsorption, DSC composed of only TAs does not show the best efficiency result due to the crack generation. In conclusion, to produce the best photocurrent conversion efficiency, the high specific surface area of TiO2 photoelectrode for high dye adsorption should be balanced with proper control of the good electron transfer path.     

Fabrication of 3D interconnected porous TiO2 nanotubes templated by poly(vinyl chloride-g-4-vinyl pyridine) for dye-sensitized solar cells

Porous TiO(2) nanotube arrays with three-dimensional (3D) interconnectivity were prepared using a sol-gel process assisted by poly(vinyl chloride-graft-4-vinyl pyridine), PVC-g-P4VP graft copolymer and a ZnO nanorod template. A 7 μm long ZnO nanorod array was grown from the fluorine-doped tin oxide (FTO) glass via a liquid phase deposition method. The TiO(2) sol-gel solution templated by the PVC-g-P4VP graft copolymer produced a random 3D interconnection between the adjacent ZnO nanorods during spin coating. Upon etching of ZnO, TiO(2) nanotubes consisting of 10-15 nm nanoparticles were generated, as confirmed by wide-angle x-ray scattering (WAXS), energy-filtering transmission electron microscopy (EF-TEM) and field-emission scanning electron microscopy (FE-SEM). The ordered and interconnected nanotube architecture showed an enhanced light scattering effect and increased penetration of polymer electrolytes in dye-sensitized solar cells (DSSC). The energy conversion efficiency reached 1.82% for liquid electrolyte, and 1.46% for low molecular weight (M(w)) and 0.74% for high M(w) polymer electrolytes.     

Carbon nanotube-nanocrystal heterostructures fabricated by electrophoretic deposition

Alternating layer, carbon nanotubes-nanocrystal composite films, comprising multi-walled carbon nanotubes (MWCNTs) and iron oxide (Fe(3)O(4)) nanocrystals, have been fabricated via electrophoretic deposition (EPD) on stainless steel and gold substrates. Low field-high current and high field-low current EPD schemes were integrated to produce the composite films. The low field-high current EPD approach produced porous mats from an aqueous suspension of the MWCNTs, while the high field-low current EPD approach produced tightly packed nanocrystal films from a dispersion of the nanocrystals in hexane. Large electric fields applied during the nanocrystal EPD and strong van der Waals interactions among the nanocrystals facilitated the formation of tightly packed nanocrystal films atop the MWCNT mats to create CNT mat-nanocrystal film composites. The surface coverage and homogeneity of the nanocrystal films improved with repeated deposition of the nanocrystals on the same mat. The assembly of nanotube mats on top of the CNT mat-nanocrystal film composite confirmed the feasibility of multilayered CNT mat-nanocrystal film heterostructures suitable for a range of devices. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques were employed to characterize the surface coverage, homogeneity, and topology of these composite films.     

Effects of TiO2 structures in dye-sensitized solar cell

In this work, the effects of crystalline structure of the TiO2, which is incorporated in fabrication of the n-type electrode, on the DSSC performance were investigated in terms of the energy conversion efficiency. In this effort, TiO2 nanoparticle pastes with varying contents of rutile and anatase structures were prepared by using the ethanol mixing method. The most efficient photo-electro-chemical performance was achieved for the DSSC fabricated with the TiO2 paste in which the anatase form of the nanocrystal extends to 90%.     

Preparation of low-crystalline apatite nanoparticles and their coating onto quartz substrates

We prepared low-crystalline apatite nanoparticles and coated them onto a surface of a Au/Cr-plated quartz substrate by the electrophoretic deposition (EPD) method or by using a self-assembled monolayer of 11-mercaptoundecanoic acid (SAM method). Low-crystalline apatite nanoparticles around 10?nm in size with extremely low contents of undesirable residual products were obtained by adding (NH(4))(2)HPO(4) aqueous droplets into a modified synthetic body fluid solution that contained Ca(CH(3)COO)(2). The apatite nanoparticles were successfully coated by either the EPD method or the SAM method; the nanoparticle coating achieved by the SAM method was more uniform than that achieved by the EPD method. The present SAM method is expected to be a promising technique for obtaining a quartz substrate coated with apatite nanoparticles, which can be used as a quartz crystal microbalance device.     

高能球磨和溶胶凝胶制备碳纳米管掺杂TiO2复合粉及其性能

采用高能球磨法和溶胶-凝胶方法制备了碳纳米管掺杂的Ti02纳米复合粉体,通过扫描电子显微镜、X射线衍射、紫外分光光度计等方法对比分析了复合粉体的形貌、微观结构以及光催化活性.实验结果表明,5％碳纳米管掺杂的Ti02复合粉体的光催化活性得到了有效提高,其中高能球磨法制备的复合粉体颗粒细小、分布均匀,具有更好的光催化活性和...     

介孔TiO2微球水热法合成及在染料敏化太阳能电池中的应用

以Ti(SO4)2为钛源,采用尿素辅助水热法合成了介孔TiO2微球,利用XRD、FESEM和比表面积分析仪对样品的晶型、形貌和比表面积进行分析,探讨了尿素加入量对TiO2微球的颗粒尺寸、比表面积、孔径和孔容的影响。采用刮涂法,用所合成的介孔TiO2微球制备了染料敏化太阳能电池(DSSC)的光阳极,结果表明,尿素用量为1.2g合成的介孔TiO2微球所组装的电池在模拟太阳光的照射下(100mW/cm2,AM1.5),光电转换效率为6.2%,明显高于商用P25纳晶所组装的电池光电转换效率(4.24%)。     

Mesoporous TiO2 films fabricated using atmospheric pressure dielectric barrier discharge jet

TiO2 nanoparticles were synthesized by a facile method of dielectric barrier discharge jet (DBD jet) for the dye-sensitized solar cell (DSSC) and other potential applications. DBD jet is utilized as a method for deposition of TiO2 nanoparticles with a 9 μm/min growth rate which is more than ×25 faster than reported previously. Their performance was compared with cells fabricated using commercial TiO2 nanoparticles (P25). The crystallinity and chemical bonding states of samples were characterized by XRD and XPS. Photoanodes fabricated by the DBD jet method resulted in approximately 50% higher photoconversion efficiency than ones prepared from P25 nanoparticles.     

Preparation and properties of a carbon nanotube-based nanocomposite photoanode for dye-sensitized solar cells

This study fabricates dye-sensitized solar cells (DSSCs) based on TiO(2)/multi-walled carbon nanotube (MWCNT) nanocomposite photoanodes obtained by the modified acid-catalyzed sol-gel procedure. Results show that incorporating MWCNTs into a TiO(2)-based electrode efficiently improves the physicochemical properties of the solar cell. The results of dye adsorption and cell performance measurements indicate that introducing MWCNTs would improve the roughness factor (from?834 to?1267) of the electrode and the charge recombination of electron/hole (e(-)/h(+)) pairs. These significant changes could lead to higher adsorbed dye quantities, photocurrent and DSSC cell performance. Nevertheless, a higher loading of MWCNTs causes light-harvesting competition that affects the light adsorption of the dye-sensitizer, and consequently reduces the cell efficiency. This study suggests an optimum MWCNT loading in the electrode of 0.3?wt%, and proposes a sol-gel synthesis procedure as a promising method of preparing the TiO(2)-based nanocomposite.     

Surface modified TiO2 nanostructure with 3D urchin-like morphology for dye-sensitized solar cell application

Three-dimensional (3D) urchin-like rutile TiO2 powders were synthesized by a mild hydrothermal method without any templates. An individual urchin-like TiO2 powder consists of self-assembled nanorods with a length of about 150 nm and width of about 10 nm. Additionally, the urchin-like TiO2 nanopowders were coated with an ultra-thin ZnO layer in order to modify the surface properties of the nanopowders, and the ZnO layer was confirmed by high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) analysis. The ZnO-modified TiO2 was used as a photoelectrode of a dye-sensitized solar cell (DSSC) and the solar cell performances were investigated. In comparison with bare TiO2, ZnO-modified TiO2 improved the photovoltaic performances, i.e., energy conversion efficiency, open circuit voltage, and short circuit current were increased. The higher DSSC performance of ZnO-modified TiO2 was attributed to its higher dye loading and lower charge recombination rate.     

染料敏化太阳能电池的研究进展

光导电极材料在染料敏化太阳能电池(DSSC)中起到关键作用,直接影响到太阳能电池的总效率,所以一直是DSSC研究的热点.介绍了DSSC的基本工作原理,概述了当前DSSC中最流行的TiO<,2>和ZnO两种薄膜光导电极材料的制备方法,并从结构、工艺和转换效率等方面对染料敏化TiO<,2>薄膜太阳能电池和染料敏化ZnO薄膜太阳能电池进行了介绍和讨论;同时简要介绍了目前研究非常热门的叠层染料敏化太阳电池的研究进程,最后展望了染料敏化太阳能电池的未来发展前景.     

Fabrication of a multi-scale nanostructure of TiO(2) for application in dye-sensitized solar cells

We propose a highly ordered multi-scale nanostructure of TiO(2) for applications as an anode in dye-sensitized solar cells (DSSCs). The structure is composed of a TiO(2) blocking layer, a TiO(2) inverse opal main body, regularly arranged transport channels between contacting spherical voids of the TiO(2) inverse opal, and TiO(2) nanoparticles coated on the spherical surfaces of the voids. The ordered and continuous backbone of the inverse opal serves as the fast electron transport pathways while the regularly arranged transport channels enable easy transport of dye and electrolyte within the structure. A multi-cycle procedure was developed to enable fabrication of thick inverse opals and easy adjustment of the inverse opal thickness. An example structure was constructed, involving a blocking layer of 90?nm thickness, an inverse opal of 100?nm voids, transport channels of 30-50?nm openings, and nanoparticles 10-15?nm in size. An open-circuit voltage decay investigation showed a significant improvement in electron lifetime for the proposed multi-scale TiO(2) nanostructure based DSSC than that of a TiO(2) nanoparticle film based DSSC, revealing the superior electron recombination characteristic offered by the proposed TiO(2) nanostructure. The conversion efficiency of the DSSC assembled from such an anode structure can reach 4% with a short-circuit current density (J(sc)) of 8.7?mA?cm(-2) and open-circuit potential (V(oc)) of 0.76?V under AM 1.5 (100?mW?cm(-2)) illumination.     

Effect of filler types and calcination temperature on the microstructure and the nitric oxide photocatalytic activity of composite titanium dioxide films

The composite titanium dioxide (TiO(2)) films coating on the woven glass fabric were prepared by a modified sol-gel process, using pre-calcinated TiO(2) nanoparticle or silica gel as filler. The characterized physicochemical properties of the prepared catalyst films showed that the specific surface area, the microstructure and the crystal structure of the catalysts were greatly affected by the fillers and the calcination temperature. The physicochemical properties of composite films and the photocatalytic activity of nitric oxide (NO) show that the pre-calcinated TiO(2) nanoparticle is more favorable than silica gel as filler. The pre-calcinated TiO(2) nanoparticle filler can increase the photocatalytic activities of the catalysts by increasing the specific surface area, introducing a bimodal mesoporous structure, and creating a polymorphous crystal structure. And the TiO(2)-TiO(2) film calcinated at 400 degrees C exhibits the highest photocatalytic activity for NO oxidation and is more active than Degussa P25.     

Quasi-solid-state dye-sensitized solar cells based on TiO2/NiO core-shell nanocomposites

The core-shell nanocomposites of titanium dioxide (TiO2) and nickel oxide (NiO) used as modified photoelectrode materials in a quasi-solid-state dye-sensitized solar cell (quasi-DSSC) were synthesized using TiO2 P-25 and a nickel acetate precursor, via ball milling. The as-obtained intermediate products were annealed at 350, 450, and 550 degrees C. The structural properties of the NiO/TiO2 nanocomposites were well characterized via X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The results imply that NiO-shell-coated TiO2 nanoparticles can be obtained with the assistance of sufficient thermal energy in the system. The crystallite size of the composite increased as the annealing temperature increased. Among all the prepared conditions, the composite with 0.1 wt% NiO exhibited the best performance, with an optimized solar-energy conversion efficiency of 2.29% and with a short-circuit current density of 7.21 mA/cm2. The significant enhancement of the device's current density may be associated with the charge recombination suppression by the NiO shell, which acted as a potential barrier in the composite. The decrease in the recombination of the photo-injected electrons, and the increase in the number of electrons tunneling through the NiO layer at the interface, may have resulted from the presence of a NiO layer on the TiO2 nanoparticles.     

Electrospray preparation of hierarchically-structured mesoporous TiO₂ spheres for use in highly efficient dye-sensitized solar cells

We report a simple method to prepare hierarchically structured TiO(2) spheres (HS-TiO(2)), using an electrostatic spray technique, that are utilized for photoelectrodes of highly efficient dye-sensitized solar cells (DSSCs). This method has an advantage to remove the synthesis steps in conventional sol-gel method to form nano-sized spheres of TiO(2) nanoclusters. The fine dispersion of commercially available nanocrystalline TiO(2) particles (P25, Degussa) in EtOH without surfactants and additives is electro-sprayed directly onto a fluorine-dopoed tin-oxide (FTO) substrate for DSSC photoelectrodes. The DSSCs of HS-TiO(2) photoelectrodes show high energy conversion efficiency over 10% under illumination of light at 100 mW cm(-2), AM1.5 global. It is concluded from frequency-dependent measurements that the faster electron diffusion coefficient and longer lifetime of HS-TiO(2) than those in nonstructured TiO(2) contribute to the enhanced efficiency in DSSCs.     

Preparation and characterization of the transparent hybrids of silicone epoxy resin and titanium dioxide nanoparticles via sol-gel reactions

In order to prepare transparent hybrid films of high refractive index, nanoparticles of TiO2 were prepared and dispersed in a silicone epoxy (SE) resin synthesized from diphenyl silane diol and [2-(3,4-epoxycyclohexyl)ethyl] trimethoxysilane by sol-gel reactions. It was found that amorphous TiO2 nanoparticles of about 5 nm modified with hexahydro-4-methyl phthalic anhydride [HMPA] were dispersed in the SE resin without agglomerations. The refractive index of the hybrids increased linearly with increasing the TiO2 contents. The hybrid containing 30 wt% of the TiO2 particles showed light transmittance of 94% at 450 nm and refractive index of 1.63. The fine dispersion of the TiO2 nanoparticles was attributable to the sol-gel reactions between the SE resin and TiO2 nanoparticles and the modification of the TiO2 particles with HMPA.