Films For Dye-sensitized Solar Cells Research Articles

Nanostructured Mesoporous Thick Films of Titania for Dye-Sensitized Solar Cells

For energy harvesting, such as in dye-sensitized solar cells, thick films of nanostructured mesoporous titania are inevitably required. Although various mesoporous thin films, i.e., film thickness below 300 nm, such as those of TiO2 and SiO2, have been widely investigated via a supramolecular templating approach in the past decade, little progress has been made with thick films, i.e., film thickness of at least several micrometers. In order to develop the desperately wanted thick films of mesoporous nanostructure for titania, we have successfully modified the supramolecular templating approach, where the highly crystallized mesoporous titania thick films of varying thicknesses and different morphologies are realized, resulting in the formation of highly ordered body-centered orthorhombic and disordered wormlike mesostructures. The performance of these mesoporous films in dye-sensitized solar cells has been investigated, achieving a maximum efficiency of ~7% at the film thickness of ~6 μm. The highly ordered mesoporous titania film outperforms the disordered counterpart of the same thickness in both short circuit current and efficiency. The improved cell performance of the ordered mesoporous film is shown to arise from the enhanced electron transport in the regularly packed titania network due to the enhanced crystalline grain connectivity.

Dye-Sensitized Solar Cells TiO<sub>2</sub> Thin Film Preparation and Conditions in Laboratory

The use of colloidal solution deposition method on the preparation of the nanostructured TiO2 thin film for dye-sensitized solar cells in basic laboratory conditions was introduced. The effects of reaction temperature, time, and solvents on the film properties have been investigated. The experiments show that the use of dilute acetic acid could get a stable sol; 450°C 30 minutes in oven without preheat could have ideal TiO2 thin film.

Correction to Supramolecular-Templated Thick Mesoporous Titania Films for Dye-Sensitized Solar Cells: Effect of Morphology on Performance

Correction to Supramolecular-Templated Thick Mesoporous Titania Films for Dye-Sensitized Solar Cells: Effect of Morphology on Performance

Anatase TiO 2 sols derived from peroxotitanium acid and to form transparent TiO 2 compact film for dye-sensitized solar cells

Transparent and surfactant-free TiO 2 sols containing anatase nanocrystals were prepared by the hydrothermal treatment of water-soluble peroxotitanium acid (PTA) at a temperature of 120 °C. The TiO 2 nanocrystals were characterized by transmission electron microscopy (TEM). The TEM results indicated that the TiO 2 nanocrystals were nanorod-like with diameters of less than 7 nm after the subsequently hydrothermal treatment. A gradient layer between the transparent fluorine doped SnO 2 (FTO) layer and the porous titanium dioxide nanocrystalline film for dye-sensitized solar cells (DSSCs) photoelectrodes, was made with the as-prepared TiO 2 sols. The TiO 2 gradient layers were characterized by field-emission scanning electron microscopy and UV–vis absorption spectrometry. After the gradient layer deposition on the FTO coated glass, the composite multilayer film exhibited the visible light transmittance of 80% which approached to that of bare FTO glass. The photo-to-electric energy conversion efficiency of the N719 dye-sensitized solar cell had significantly improved from 4.2% to 5.6% in the presence of the compact layer between FTO and the porous TiO 2 nanocrystalline film under of AM1.5 illumination (100 mW/cm 2). The remarkable improvements in short-circuit current for the DSSCs was due to the effective gradient layer at the FTO–TiO 2 interface which prevented direct contact of electrolytes with FTO and consequently reduced charge recombination losses.

Fabrication and Characterization of Photoelectrode Thin Films with Different Morphologies of TiO<SUB>2</SUB> 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%.

Electrodeposition of Nanostructured ZnO Films for Dye-Sensitized Solar Cells

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Layer-by-Layer Fabrication of Multiple-Dye-Sensitized TiO<SUB>2</SUB> Films for Dye-Sensitized Solar Cells by Vacuum Cold Spray

Space-separate co-sensitization allows a more flexible design of dye sensitizers and promotes the development of high performance dye-sensitized solar cells, since the negative interactions between different dyes are minimized by the spatial seperation. The key point involves depositing nano-TiO particles on the dye-loaded TiO layer to form an efficient electron transport between the outer TiO layer and the inner dye-loaded layer. Layer-by-layer fabrication of multiple-dye-sensitized TiO films was realized through high velocity impact deposition by vacuum cold spray. Results show that the effective connection between the nano-TiO particles in the outer layer and the inner dyeloaded layer was realized through the high compressive pressure pulses resulting from the high velocity particle impact on deposit surface. It is found that the photovoltaic performance of the inner dye-loaded photoanode was not influenced by the deposition of the outer layer. A significant enhancement of photocurrent was obtained by space-separate co-sensitization of N719 dye and Black dye due to the effective connection between the outer layer and the inner dye-loaded layer.

The Effect of Substrate Temperature on the Spray-Deposited TiO<SUB>2</SUB> 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.

Thickness-dependent solar power conversion efficiencies of catalytic graphene oxide films in dye-sensitized solar cells

The catalytic effects of graphene oxide (GO) films were investigated for dye-sensitized solar cell (DSSC). The GO film consisted of a networked structure of two phases of GO with intercalated H 2O and exfoliated GO. A maximum solar power conversion efficiency ( η) of 2.30% was obtained for the ultrathin GO film. This η is higher than that of other reported types of DSSCs (0.84%) and organic solar cells (1.1%) with graphene electrodes. The catalytic effect of the GO film is attributed to the good ion permeability along the interlayer hydrophilic spaces; the electrons present in these spaces on the exfoliated GO were supplied to the iodide ions.

TiO2 coated SnO2 nanosheet films for dye-sensitized solar cells

TiO2-coated SnO2 nanosheet (TiO2–SnO2 NS) films about 300nm 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%.

Electron transportation and optical properties of microstructure TiO2 films: applied in dye-sensitized solar cells

Micro-structure of TiO2 films in dye-sensitized solar cells (DSSCs) can affect light absorption and electron transportation that impact on the characteristics of currentvoltage (J-V). In this paper, films with different surface area, pore size and porosity were obtained by adding different ratio of ethyl cellulose (Ec-S) to pastes, and a photo-electric conversion efficiency (η) of 7.55% with a short-circuit current density (Jsc) of 16.81 mA·cm−2 was obtained when the ratio of Ec-S was 10:5. BET results showed that film with this optimum ratio had the most suitable pore size and surface area for good properties of photovoltaic, which had a low reflectivity and high transmission rate, and the efficiency of light utilization was improved. Moreover, measurements by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS) implied that the electron transport time (τd) increased as the content of Ec-S increased, which was related to the larger surface area. Results of steady-state cyclic voltammetry indicated that diffusion-limited current density (Jlim) of I3− in TiO2 film increased with its porosity, which revealed that the transportation of redox mediators in the electrolyte was speeded up.

Application of a Schottky barrier to dye-sensitized solar cells (DSSCs) with multilayer thin films of photoelectrodes

This study combines Au nanoparticles with TiO 2 nanoparticles to form a Schottky barrier, and applies it to the photoelectrode thin film of dye-sensitized solar cells (DSSCs). First, commercial TiO 2 powder (Degussa P25) is put in the alkaline solution to prepare for TiO nanotubes (Tnt) by using hydrothermal treatment. Tnt are sintered at 550 °C to obtain Tnt-C550 particles. In addition, TiO 2 nanoparticles (H180) prepared by subjecting Tnt to two cycles of hydrothermal treatment. H180 served as the first layer, and Tnt-C550 as the second. The third layer adopts salt reduction method to prepare for Au nanoparticles. Experimental results show that the DSSCs prepared with three layers of photoelectrode thin films (H180/Tnt-C550/Au) enhanced the light-to-electricity efficiency of DSSCs by as high as 21% (6.34–7.65%).

Improvement of mass transport of the [Co(bpy)3]II/III redox couple by controlling nanostructure of TiO2 films in dye-sensitized solar cells

Mass transport of the [Co(bpy)(3)](II/III) redox electrolyte is found to strongly depend on porosity and pore size of mesoporous TiO(2) films. Photocurrent density is improved by nearly two times with increasing the porosity from 0.52 to 0.59 despite 23% decreased dye loading. Optimized nanostructure sensitized with MK-2 dye shows efficiency of 5.5% at 1 sun.

Microwave assisted CdSe quantum dot deposition on TiO2 films for dye-sensitized solar cells

CdSe quantum dot (QD ) sensitized TiO(2) films have been fabricated using a one-step microwave assisted chemical bath deposition (MACBD) technique and used as photoanodes for quantum dot sensitized solar cells. This technique allows direct and rapid deposition and a good contact between the CdSe and TiO(2) films. The photovoltaic performances of the cells with CdSe deposited at different times are investigated. The results show that cells based on MACBD deposited TiO(2)/CdSe electrodes achieve a maximum short circuit current density of 12.1 mA cm(-2) and a power conversion efficiency of 1.75% at one Sun (AM 1.5 G, 100 mW cm(-2)), which is comparable with those fabricated using conventional techniques.

Effects of 4-tert-butylpyridine on the quasi-Fermi levels of TiO2 films in the presence of different cations in dye-sensitized solar cells

The effects of additives on the quasi-Fermi levels (QFL) of TiO(2) films in dye-sensitized solar cells (DSCs) were investigated by a direct method. We observed that the values of QFL of TiO(2) at short circuit and open circuit are different and found for the first time the linear relationships between QFL shifts at short circuit and open circuit induced by 4-tert-butylpyridine (TBP), and that the slopes of the lines were significantly influenced by the nature of cations in the electrolyte. Different QFL shifts at short circuit and open circuit were observed in the presence of TBA(+). These quantitative results suggest that the QFL of TiO(2) films at short circuit and open circuit can be adjusted separately by developing suitable additives and cations, which will be helpful to further improve the efficiency of DSCs.

Effect of the molecular weight of a polyethylene glycol on the photoluminescence spectra of porous TiO 2 films for dye-sensitized solar cells

Dye-sensitized solar cells (DSCs) are expected to be used for future clean energy. In general, when the titania porous electrode in DSCs is made, a polyethylene glycol (PEG) is added to obtain the porous structure. Although the conversion efficiency of the DSC became high when the high molecular weight of PEG was used, its reason was not clear. In the present study, the photoluminescence spectrum of titania films with the different molecular weight of PEG was measured at room temperature, and we discussed the relation between molecular weight and the conversion efficiency of the DSC.

Preparation and Characterization of Pure Rutile TiO2Nanoparticles for Photocatalytic Study and Thin Films for Dye-Sensitized Solar Cells

Pure rutile-phase TiO2(r-TiO2) was synthesized by a simple one pot experiment under hydrothermal condition using titanium (IV) n-butoxide as a Ti-precursor and HCl as a peptizer. The TiO2products were characterized by XRD, TEM, ESCA, and BET surface area measurement. The r-TiO2were rodlike in shape with average size of nm at hydrothermal temperature of 220°C for 10 h. Hydrothermal treatment at longer reaction time increased the tendency of crystal growth and also decreased the BET surface area. The degradation of methylene blue was selected as a test reaction to confer the photocatalytic activity of as-obtained r-TiO2. The results showed a strong correlation between the structure evolution, particle size, and photocatalytic performance of r-TiO2. Furthermore, the r-TiO2-based solar cell was prepared for the photovoltaic characteristics study, and the best efficiency of ~3.16% was obtained.

Modification of TiO2 electrode films in dye-sensitized solar cells with PMMA

Nanocrystalline porous TiO2 electrodes for dye-sensitized solar cells (DSC) are modified by adding polymethyl methacrylate (PMMA). The result shows that large holes are formed in the TiO2 films, and the short circuit photocurrent density and photoelectric conversion efficiency of DSCs are obviously enhanced compared with those without adding the PMMA. The relationship between the photoelectric conversion efficiency and the amount of PMMA is presented. In particular, the highest conversion efficiency was obtained with TiO2 electrode films of adding 7.5 wt% PMMA, increasing the conversion efficiency by 27.5%.

Role of Polyelectrolyte for Layer-by-Layer Compact TiO2 Films in Efficiency Enhanced Dye-Sensitized Solar Cells

Efficient compact TiO2 films using different polyelectrolytes are prepared by the layer-by-layer technique (LbL) and applied as an effective contact and blocking film in dye-sensitized solar cells (DSCs). The polyanion thermal stability plays a major role on the compact layers, which decreases back electron transfer processes and current losses at the FTO/TiO2 interface. FESEM images show that polyelectrolytes such as sodium sulfonated polystyrene (PSS) and sulfonated lignin (SL), in comparison to poly(acrylic acid) (PAA), ensure an adequate morphology for the LbL TiO2 layer deposited before the mesoporous film, even after the sintering step at 450 °C. The so treated photoanode in DSCs leads to a 30% improvement on the overall conversion efficiency. Electrochemical impedance spectroscopy (EIS) is employed to ascertain the role of the compact films with such polyelectrolytes. The significant increase in Voc of the solar cells with adequate polyelectrolytes in the LbL TiO2 films shows their pivotal role in ...

Preparation of anatase TiO 2 thin films for dye-sensitized solar cells by DC reactive magnetron sputtering technique

Anatase titanium dioxide (TiO 2) 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 TiO 2 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 TiO 2 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.