The effect of substrate temperature on the spray-deposited TiO2 nanostructured films for dye-sensitized solar cells

The nanostructured TiO2 films have deposited on SnO2:F (FTO) coated glass substrate by spray pyrolysis technique at different substrate temperatures of 200-500 degrees C. The structural, surface morphological and optical properties of TiO2 films significantly vary with the substrate temperature. The surface of the TiO2 films deposited at 400 degrees C shows the nanoflakes and short nanorods (approximately 130 nm) like structures while the TiO2 films prepared at 500 degrees C shows only the nanoflakes like structures. The band gap of the TiO2 films prepared at higher temperatures (300-500 degrees C) becomes narrow due to presence the rutile phases in their crystal structure. Ruthenium (II) complex as a dye, KI/I2 as an electrolyte and carbon on FTO glass as a counter electrode has used to fabricate the dye-sensitized solar cell (DSC). The TiO2 film deposited at 400 degrees C has showed the best photovoltaic performance in DSC with the efficiency of 3.81%, the photovoltage of 773 mV, the photocurrent of 8.34 mA/cm2, and the fill factor of 56.17%. The photovoltage of the DSC increases with the increase of substrate temperature during the deposition of TiO2 films. Moreover, all the DSCs exhibit reasonably high fill factor value.     

Fabrication of dye-sensitized solar cells using Nb2O5 blocking layer made by sol-gel method

In this study, nanocrystalline Nb2O5 thin film has been prepared via sol-gel process using niobium ethoxide as a precursor. Sol-gel films using various ratios of H2O/Nb have been prepared on fluorinated tin oxide (FTO) glass substrate, and used as electron-blocking layer of dye-sensitized solar cell (DSSC). The Nb2O5 film as deposited was amorphous, but became crystalline with hexagonal phase after heat treatment at 600 degrees C. With higher H2O/Nb molar ratio, denser and more uniform Nb2O5 film surface was obtained. DSSCs with the structure of FTO/Nb2O5/TiO2/Dye/EL/Pt/FTO have been prepared, and their solar-cell performance was evaluated. By introduction of Nb2O5 sol-gel film between FTO and TiO2 layer in DSSCs, energy conversion efficiency could be improved.     

染料敏化太阳能电池阻挡层的制备及其性能研究

采用电子束蒸发法在光阳极导电玻璃基底上制备了一层致密的TiO2薄膜,并在氧氛围下进行不同温度的退火处理。以此TiO2薄膜为阻挡层来阻止电解质溶液中I3-与导电玻璃基底上光生电子的复合。分别利用X射线衍射（XRD）和X射线光电子能谱（XPS）对此薄膜的结构和成分进行表征。制备不同厚度的TiO2阻挡层薄膜并研究其对电池光电性能的影响。实验结果表明,阻挡层的引入有效地抑制了暗反应的发生,提高了染料敏化太阳能电池（DSSC）的开路电压、短路电流和光电转换效率,比未引入阻挡层的DSSC的光电转换效率提高了31.5%。     

Nanostructured TiO2 films for dye-sensitized solar cells prepared by the sol-gel method

TiO2 films were prepared on glass substrates using the sol-gel process for a dye-sensitized solar cell application. The TiO2 sol was prepared using hydrolysis/polycondensation. Titanium (IV) Tetra Isopropoxide (TTIP) was used as precursor and Nitric acid (HNO3) was used as a catalyst for the peptization. The crystal structure and morphology of the prepared materials were characterized by XRD, and an SEM. The observations confirmed the nanocrystalline nature of the TiO2. The reaction parameters, such as the catalyst concentrations, the calcination time, and the calcination temperature were varied during the synthesis in order to achieve nanosize TiO2 particles. The prepared TiO2 particles were coated onto FTO glass using a screen printing technique. The prepared TiO2 films were characterized by UV-vis. The TiO2 particles calcinated at low temperatures showed an anatase phase they grew into a rutile phase when the calcination temperature increased. The size and structure of the TiO2 particles were adjusted to specific surface areas. It was found that the conversion efficiency of the DSSC was highly affected by the properties of the TiO2 particles.     

Improvement in performances of dye-sensitized solar cell with SiO2-coated TiO2 photoelectrode

The pure TiO2 and the nano-porous SiO2-coated TiO2 (STO) films were deposited on the FTO substrates by spray technique for the application of dye-sensitized solar cells (DSSCs). XRD pattern shows the pure TiO2 and STO films exhibits the same structure. We found that there is no much difference in dye absorption between the STO and the pure TiO2 films. The electrochemical impedance spectra reveal that insulating nature of the porous SiO2 increases surface resistance of the TiO2 film and supresses back transfer of the photogenerated electrons to the electrolyte. The field-emission scanning electron microscopy (FE-SEM) and energy dispersion X-ray spectroscopy (EDS) reveal that the surface morphology and the existence of SiO2 layer on the surface of the TiO2 films, respectively. The photoelectrochemical results show that the short-circuit photocurrent (J(SC)) increased from 16.73 mA cm(-2) to 18.31 mA cm(-2) and the open-circuit voltage (V(OC)) value changed from 0.71 V to 0.74 V for the STO films. The efficiency of cell has been greatly improved from 8.25 to 9.3%.     

TiO2 paste formulation for crack-free mesoporous nanocrystalline film of dye-sensitized solar cells

Using a doctor-blade method, a highly viscous titanium dioxide (TiO2) paste was deposited on a glass substrate coated with fluorine doped tin oxide (FTO). The paste was mainly composed of commercially available TiO2 nanoparticles (P25) and hydroxypropyl cellulose (HPC) as organic filler. Varying the content of HPC in the TiO2 paste changed the physical properties of the mesoporous TiO2 layer, particularly its porosity and surface area. From the quantification of dyes on Ti2, layer and the electrochemical impedance spectroscopy (EIS) study of the dye-sensitized solar cells (DSSCs), the surface area of the TiO2 film was found to have decreased. This came with the increase of HPC content while the porosity of the film increased, consistent with the concurrent decrease of short-circuit current density (Jsc) and efficiency (eta). The increased porosity greatly affected the electron transport through the TiO2 film by decreasing the coordination number of the TiO2 particles resulting to a decrease of the electron diffusion coefficient.     

Electrospinning processed nanofibrous TiO(2) membranes for photovoltaic applications

We have recently fabricated dye-sensitized solar cells (DSSCs) comprising nanofibrous TiO(2) membranes as electrode materials. A thin TiO(2) film was pre-deposited on fluorine doped tin oxide (FTO) coated conducting glass substrate by immersion in TiF(4) aqueous solution to reduce the electron back-transfer from FTO to the electrolyte. The composite polyvinyl acetate (PVac)/titania nanofibrous membranes can be deposited on the pre-deposited thin TiO(2) film coated FTO by electrospinning of a mixture of PVac and titanium isopropoxide in N,N-dimethylformamide (DMF). The nanofibrous TiO(2) membranes were obtained by calcining the electrospun composite nanofibres of PVac/titania as the precursor. Spectral sensitization of the nanofibrous TiO(2) membranes was carried out with a ruthenium (II) complex, cis-dithiocyanate-N,N(')-bis(2,2(')-bipyridyl-4,4(')-dicarboxylic acid) ruthenium (II) dihydrate. The results indicated that the photocurrent and conversion efficiency of electrodes can be increased with the addition of the pre-deposited TiO(2) film and the adhesion treatment using DMF. Additionally, the dye loading, photocurrent, and efficiency of the electrodes were gradually increased by increasing the average thickness of the nanofibrous TiO(2) membranes. The efficiency of the fibrous TiO(2) photoelectrode with the average membrane thickness of 3.9?μm has a maximum value of 4.14%.     

Novel counter electrodes based on NiP-plated glass and Ti plate substrate for dye-sensitized solar cells

Novel counter electrodes based on NiP-plated glass and Ti plate substrate were prepared by thermal decomposition of H₂PtCl₆. Their properties and application in dye-sensitized solar cells were investigated. Platinized Ti plate electrode (Pt/TP electrode) and platinized NiP-plated glass electrode (Pt/NiP electrode) exhibited the same electrochemical activity for triiodide reduction as platinized fluorine-dope tin oxide (FTO) conducting glass electrode (Pt/FTO electrode). However, Pt/NiP electrode and Pt/TP electrode have the advantage over the Pt/FTO electrode in increasing the light reflectance and reducing the sheet resistance, which resulted to improve the light harvest efficiency and the fill factor of the dye-sensitized solar cells effectively. Examination of the anodic dissolution indicated the good stability of the Pt/NiP electrode and Pt/TP electrode in the electrolyte containing iodide/triiodide.     

Preparation of nanorod-like anatase TiO2 nanocrystals and their photovoltaic properties

Anatase TiO2 nanocrystals with the high specific surface area were prepared by the hydrothermal treatment of anatase TiO2 sols at the temperature of 150 degrees C and above. When TiO2 sols with a lower content of TiO2 and at a relatively high pH value were hydrothermal treated, the dispersible and nanorod-like TiO2 nanocrystals were formed via the oriented attachment. The nanorod-like TiO2 nanocrystals with an aspect ratio of larger than 5 and a mean diameter of less than 7 nm were obtained in the absence of organic compounds. The as-prepared TiO2 nanocrystals were characterized with X-ray diffraction, transmission electron microscopy and BET surface area techniques. The TiO2 nanostructures were deposited on the FTO conductive glass as the anodic electrode for the dye-sensitized solar cells (DSSCs) and assembled into solar cells. The derived solar cells showed a conversion efficiency of 6.12% under 1 sun illumination of simulated sunlight and external quantum efficiency (EQE) of more than 60% at the wavelength of 550 nm. The DSSCs from the anatase nanorods has a higher open circuit voltage compared to the spherical nanocrystals.     

The function of a TiO2 compact layer in dye-sensitized solar cells incorporating "planar" organic dyes

We present a device based study into the operation of liquid electrolyte dye-sensitized solar cells (DSSC's) using organic dyes. We find that, for these systems, it is entirely necessary to employ a compact TiO2 layer between the transparent fluorine doped SnO2 (FTO) anode and the electrolyte in order to reduce charge recombination losses. By incorporation of a compact layer, the device efficiency can be increased by over 160% under simulated full sun illumination and more than doubled at lower light intensities. This is strong evidence that the more widely employed ruthenium based sensitizers act as to "insulate" the anode against recombination losses and that many planar organic dyes employed in DSSC's could greatly benefit from the use of a compact TiO2 blocking layer. This is in strong contrast to DSSC's sensitized with ruthenium based systems, where the introduction of compact TiO2 has only marginal effects on conversion efficiencies.     

Copper oxide thin film and nanowire as a barrier in ZnO dye-sensitized solar cells

The ZnO dye-sensitized solar cells (DSSCs) with different photoelectrodes were studied on the effect of CuO layer as a barrier layer toward power conversion characteristics. The structures of DSSCs based on ZnO as a photoelectrode, Eosin-Y as a dye sensitizer, iodine/iodide solution as an electrolyte and Pt/FTO as a counterelectrode. CuO powder, nanowire prepared by oxidation reaction of copper powder and CuO thin film prepared by evaporation copper thin film, were used as a layer on the top of ZnO layer to form blocking layer. The photocurrent, photovoltage and power conversion efficiency characteristics for DSSCs were measured under illumination of simulated sunlight obtained from a solar simulator with the radiant power of 100 mW/cm². It was found that ZnO DSSCs with CuO thin film exhibited highest current density of 5.10 mA/cm² and highest power conversion efficiency of 0.92% than those of CuO powder and nanowire. The enhancement of the power conversion efficiency can be explained in terms of the retardation of the interfacial recombination dynamics of CuO blocking layer.     

Effects of calcination temperatures on photocatalytic activity of SnO2/TiO2 composite films prepared by an EPD method

SnO2/TiO2 composite films were fabricated on transparent electro-conductive glass substrates (F-doped SnO2-coated glass:FTO glass) via an electrophoretic deposition (EPD) method using Degussa P25 as raw materials, and were further characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM), UV-vis diffuse reflectance spectra and Photoluminescence spectra (PL). XRD and XPS results confirmed that the films were composed of TiO2 and SnO2. FESEM images indicated that the as-prepared TiO2 films had roughness surfaces, which consisted of nano-sized particles. The effects of calcination temperatures on the surface morphology, microstructures and photocatalytic activity of SnO2/TiO2 composite films were further investigated. All the prepared SnO2/TiO2 composite films exhibited high photocatalytic activities for photocatalytic decolorization of Rhodamine-B aqueous solution. At 400 degrees C, the SnO2/TiO2 composite films showed the highest photocatalytic activity due to synergetic effects of low sodium content, good crystallization, appropriate phase composition and slower recombination rate of photogenerated charge carriers.     

Electrical and structural characterization of plasma polymerized polyaniline/TiO2 heterostructure diode: a comparative study of single and bilayer TiO2 thin film electrode

A heterostructure was fabricated using p-type plasma polymerized polyaniline (PANI) and n-type (single and bilayer) titanium dioxide (TiO2) thin film on FTO glass. The deposition of single and bilayer TiO2 thin film on FTO substrate was achieved through doctor blade followed by dip coating technique before subjected to plasma enhanced polymerization. To fabricate p-n heterostructure, a plasma polymerization of aniline was conducted using RF plasma at 13.5 MHz and at the power of 120 W on the single and bilayer TiO2 thin film electrodes. The morphological, optical and the structural characterizations revealed the formation of p-n heterostructures between PANI and TiO2 thin film. The PANI/bilayer TiO2 heterostructure showed the improved current-voltage (I-V) characteristics due to the substantial deposition of PANI molecules into the bilayer TiO2 thin film which provided good conducting pathway and reduced the degree of excitons recombination. The change of linear I-V behavior of PANI/TiO2 heterostructure to non linear behavior with top Pt contact layer confirmed the formation of Schottky contact at the interfaces of Pt layer and PANI/TiO2 thin film layers.     

Hydrothermal synthesis of one-dimensional single-crystalline rutile TiO2 nanostructures and their application in dye-sensitized solar cells

One-dimensional (1D) TiO2 nanowire arrays are fabricated on transparent conducting substrates via a low temperature hydrothermal route for application in dye-sensitized solar cells (DSSCs). The as-prepared sample on fluorine-doped tin oxide (FTO) substrate is found to be single-crystalline rutile TiO2 structures from X-ray and electron diffractions. The length and diameter of the nanowires depend mainly on the growth time and temperature. With increasing the reaction time, the growth rate becomes slower and the interface adhesion between the growth nanowires and the substrate becomes weaker. In the same time the adjacent nanowires aggregate to larger the apparent diameter of the nanowire making the gaps among the nanowires to disappear at last. The nanowires exhibit flower-like morphology on the non-conducting surface of FTO substrate. By using TiO2 nanowire arrays with 2 microm long on FTO substrate as the photoanode in DSSCs, an overall light conversion efficiency of 1.58% is achieved with an open circuit voltage of 0.714 V, a short circuit current density of 4.68 mA cm(-2), and a fill factor of 0.472.     

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.     

TiO2\FTO镀膜玻璃色饱和度的数值模拟

本文以具有较高折射率的材料——二氧化钛(TiO2)替代自身折射率较低的材料——SiCOx作为氟掺杂氧化锡(FTO)镀膜玻璃中间层薄膜,通过数值模拟计算的方法主要研究了TiO2\FTO镀膜玻璃的表面色饱和度控制表现,并与传统的SiCOx\FTO镀膜玻璃就色饱和度控制表现进行了对比,结果发现TiO2\FTO镀膜玻璃具有更加优异的表面色饱和度控制表现,适合进行实际应用推广。     

TiO₂ photoanode structure with gradations in V concentration for dye-sensitized solar cells

V-TiO?(GC) photoanode film with graduated structure was prepared in a dye-sensitized solar cell work electrode by layer-by-layer method using TiO? precursor with gradations in V concentration on the indium tin oxide transparent conducting glass from substrate to surface. The effects of the gradient in V concentration on the structures and properties of TiO? photoanode film were discussed. The structure of the gradient V concentration has remarkable influence on the final performance of the DSSCs and I-V characteristic measurement indicates an enhanced efficiency by 31% as compared to pure TiO? nanoparticles film samples due to abundant solar light, fast injection and transmission velocity and the slowdown recombination of photoexcited electrons, simultaneously.     

Photovoltaic performance of dye-sensitized solar cell low temperature growth of ZnO nanorods using chemical bath deposition

Nanostructured ZnO photoelectrodes were synthesized on fluorine-doped tin oxide (FTO) glass substrates that were spin-coated with a sol-gel based ZnO seed layer via a chemical bath deposition (CBD) method at varying times of 1, 2, 4, and 8 h. Then, TiO2 nanoparticulate electrodes were prepared on ZnO nanorods using the doctor blade technique. The uniformly grown ZnO nanorod layer had a length of approximately 710 nm on the FTO glass substrate with wurtzite structures which was confirmed through X-ray diffraction patterns. The length and diameter of the ZnO nanorods increased with an increase in the deposition time. The DSSCs fabricated with TiO2 nanoparticulate/grown ZnO nanorods and grown for 8 h showed the maximum efficiency (5.51%) with a short circuit current density (J(sc)) of 12.21 mA/cm2 and an open circuit voltage (V(oc)) of 0.70 at 100 mW/cm2 light intensity.     

Plasma treatment effect on dye-sensitized solar cell efficiency of hydrothermal-processed TiO2 nanorods

Atmospheric plasma (AP) treatment was carried out on TiO2 nanorods (NRs) that were hydrothermally grown on F-doped SnO2 (FTO)/glass. The effects of AP treatment on the surface of the TiO2 NRs were investigated, where the treatment involved the use of the reactive gases H2, N2, and O2. The surface energy of AP-treated TiO2 NRs was about 1.5 times higher than that of untreated TiO2 NRs (364.3 mJ/m2). After AP treatment, the increase of the peak area ratios of the Ti2O3 and TiO2 peaks in the XPS spectra resulted in a decrease in the number of oxygen vacancies in the TiO2 NRs. The efficiency of a dye-sensitized solar cell (DSSC) based on the N2-plasma-treated TiO2 NRs, which was approximately 1.11%, was about 79% higher than that of a DSSC based on the untreated TiO2 NRs.     

丝网印刷法制备染料敏化太阳能电池光电性能的研究

采用水热法制备TiO2纳米颗粒,将获得的TiO2纳米颗粒制备成胶体,采用丝网印刷法在FTO表面刷涂制备染料敏化太阳能电池（DSSC）光阳极,通过扫描电子显微镜对电极表征和电池光电性能测试,探讨印刷层数及入射光强对DSSC光电性能的影响,实验结果表明,将制备的光阳极组装成电池后具有较好的光电性能,当印刷层数为8层、光强为80W／m2时,电池取得最好的光电性能。