Layer In Dye-sensitized Solar Cells Research Articles

Deposition of TiO 2 layers for dye-sensitized solar cells using nano-particle deposition system

A novel method was applied for the deposition of TiO 2 powders using Nano-Particle Deposition System (NPDS) for a dye-sensitized solar cell (DSSC). NPDS is a method used to deposit ceramic and metallic powders on substrates at room temperature by accelerating particles to subsonic speeds. In this study, TiO 2 powders were directly sprayed on transparent conductive oxide (TCO) glass at room temperature. TiO 2 powder deposition resolved problems common to conventional pastes of TiO 2 powders, such as crack formation and poor adhesion on substrates. Using this dry-coating method, the maximum light-conversion efficiency of the fabricated cell was 2.86% with a photocurrent density of 7.72 mA cm −2. The cell efficiency improved when the sealing-sheet thickness was 25 μm because the amount of electrolyte in the cell was optimized to prevent unnecessary recombination of electrons and holes. Therefore, sealing-sheet thickness is crucial in maximizing photovoltaic efficiency. Overall, this study proved that dry-coating of TiO 2 is possible for DSSC, and this method can also be applied on flexible substrates.

Effects of Insulation Coating with Metal Salt on the Performance of Organic-Inorganic Hybrid Solar Cells

This work reports on the preparation of modified TiO2 electrodes, which could be applied to the photoanodes in a dye-sensitized solar cells (DSSCs). TiO2 layer was formed on a FTO (fluorine-doped tin oxide) coated glass via doctor-blade method and post heat treatment. Then, the various metal hydroxides and metal oxides were selectively deposited onto the TiO2 layers via electrophoretic deposition and annealing process to give modified TiO2 layer in DSSCs. When metal hydroxide-deposited electrodes were employed in DSSCs, photovoltaic efficiencies were improved by ca. 3–16% compared to those of the cells with bare TiO2 electrodes. However, it was found that the efficiencies regressed when the metal hydroxides were converted to metal oxides via the annealing process.

Efficient Performance of Electrostatic Spray-Deposited TiO2 Blocking Layers in Dye-Sensitized Solar Cells after Swift Heavy Ion Beam Irradiation.

A compact TiO2 layer (~1.1 μm) prepared by electrostatic spray deposition (ESD) and swift heavy ion beam (SHI) irradiation using oxygen ions onto a fluorinated tin oxide (FTO) conducting substrate showed enhancement of photovoltaic performance in dye-sensitized solar cells (DSSCs). The short circuit current density (Jsc = 12.2 mA cm-2) of DSSCs was found to increase significantly when an ESD technique was applied for fabrication of the TiO2 blocking layer, compared to a conventional spin-coated layer (Jsc = 8.9 mA cm-2). When SHI irradiation of oxygen ions of fluence 1 × 1013 ions/cm2 was carried out on the ESD TiO2, it was found that the energy conversion efficiency improved mainly due to the increase in open circuit voltage of DSSCs. This increased energy conversion efficiency seems to be associated with improved electronic energy transfer by increasing the densification of the blocking layer and improving the adhesion between the blocking layer and the FTO substrate. The adhesion results from instantaneous local melting of the TiO2 particles. An increase in the electron transport from the blocking layer may also retard the electron recombination process due to the oxidized species present in the electrolyte. These findings from novel treatments using ESD and SHI irradiation techniques may provide a new tool to improve the photovoltaic performance of DSSCs.

Anatase Nanowires: Application to Functional Light Scattering Layers in Dye-Sensitized Solar Cells

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Method for fabricating the compact layer in dye-sensitized solar cells by titanium sputter deposition and acid-treatments

Dye-sensitized solar cells (DSCs) have been put forward as a potential low-cost alternative to the widely used silicon solar cells, which are subject to cost limitations. However, some problems need to be solved in order to enhance the efficiency of DSCs. In particular, the electron recombination occurred by the contact between the transparent conductive oxide (TCO) and a redox electrolyte is one of the main limiting factors of efficiency. Accordingly, a compact layer plays an important role in realizing highly efficient DSCs because it improves the adhesion of the TiO 2 to the TCO and provides a larger contact area and more effective electron transfer by preventing electron recombination. In this work, the fabrication of a TiO 2 compact layer using Ti sputter deposition and acid-treatment was investigated rather than the conventional method, which uses a TiCl 4 aqueous solution. The acid-treatment of the sputtered Ti film actively oxidized the Ti particles. As a result, such a cell exhibited an additional 1.3% in total efficiency compared to the standard DSC without a compact layer. These improvements are not inferior to those obtained by the conventional fabrication method using a TiCl 4 aqueous solution.

Dye-sensitized solar cells using anodic TiO 2 mesosponge: Improved efficiency by TiCl 4 treatment

In the present work, we produce 15 μm thick titania mesosponge layers (TMSL) by a Ti anodization/etching process and use the layers in dye-sensitized solar cells (DSCs). We show that the solar cell efficiency can considerably be improved by a TiCl 4 hydrolysis treatment (increase of approx. 40% to an overall value of 4.9% under AM 1.5 illumination). This beneficial effect is due to the decoration of the ∼10 nm wide channels present in TMSL with TiO 2 nanoparticles of approx. 3 nm diameter, which allow for a significantly higher specific dye loading of the TMS structure.

Sponge-like TiO2 layers for dye-sensitized solar cells

A titanium oxide layer used in a dye-sensitized solar cell (DSSC) has to meet two opponent properties to enable high conversion efficiency: a large surface area (for high dye loading) and good connection between TiO2 grains (for efficient extraction of electrons toward the front contact). In order to meet a trade-off between these criteria a preparation method for TiO2 paste formulation based on Pechini sol–gel method and commercial nanocrystalline TiO2 powder has been developed. A series of TiO2 pastes with different molar ratios between titanium isopropoxide, citric acid and ethylene glycol (1:X:4X) in the paste have been examined. The structure and morphology as well as cross-cut tests of deposited and sintered TiO2 layers have been analyzed. Results reveal that the paste with X = 8 exhibits the best properties, resulting in an overall conversion efficiency of DSSC under standard test conditions (100 mW/cm2, 25 °C, AM 1.5G) up to 6.6% for ionic liquid based electrolyte.

Hydrothermal Growth and Application of ZnO Nanowire Films with ZnO and TiO2Buffer Layers in Dye-Sensitized Solar Cells

This paper reports the effects of the seed layers prepared by spin-coating and dip-coating methods on the morphology and density of ZnO nanowire arrays, thus on the performance of ZnO nanowire-based dye-sensitized solar cells (DSSCs). The nanowire films with the thick ZnO buffer layer (~0.8–1 μm thick) can improve the open circuit voltage of the DSSCs through suppressing carrier recombination, however, and cause the decrease of dye loading absorbed on ZnO nanowires. In order to further investigate the effect of TiO2buffer layer on the performance of ZnO nanowire-based DSSCs, compared with the ZnO nanowire-based DSSCs without a compact TiO2buffer layer, the photovoltaic conversion efficiency and open circuit voltage of the ZnO DSSCs with the compact TiO2layer (~50 nm thick) were improved by 3.9–12.5 and 2.4–41.7%, respectively. This can be attributed to the introduction of the compact TiO2layer prepared by sputtering method, which effectively suppressed carrier recombination occurring across both the film–electrolyte interface and the substrate–electrolyte interface.

Preparations of TiO 2 pastes and its application to light-scattering layer for dye-sensitized solar cells

Three different structures of TiO 2 electrodes of the dye-sensitized solar cell (DSSC) devices were fabricated with layers of nanoparticles and light-scattering particles, and their photovoltaic performances were investigated when the polymer electrolytes were used. Especially, 20-nm- and 123-nm-TiO 2 pastes were prepared by using sol–gel method, to use for light-scattering layer from the incident light. The best efficiency of 6.03% under AM 1.5 was attained with a multi-layer structure using 123-nm-TiO 2 layer for the light-scattering layer and 9-nm-TiO 2 layer for the dense layer.

Zinc Borosilicate Thick Films as a Ag-Protective Layer for Dye-Sensitized Solar Cells

A zinc borosilicate glass having a low softening temperature of 490℃ has been investigated as a protective layer for Ag patterns against chemical reactions with a I?/I₃? electrolyte in dye-sensitized solar cells (DSSCs). A thick glass layer was prepared bythe typical screen printing and firing processes to obtain a final thickness of ~5 ㎛. The chemical leaching performance of theglass layer in the electrolyte revealed that the reactive Ag pattern can be significantly protected by utilizing the low softeningprotective layer. The electrical resistance of the FTO-coated glass substrate was effectively maintained at a low value of ~27 Ω aslong as the glass layer was well densified at a sufficiently high temperature of ~520℃. The transmittance of the layer was near 60%, depending on the firing temperature of the glass layer.

Layer-by-layer TiO 2 films as efficient blocking layers in dye-sensitized solar cells

Charge recombination at the conductor substrate/electrolyte interface has been prevented by using efficient blocking layers of TiO 2 compact films in dye-sensitized solar cell photoanodes. Compact blocking layers have been deposited before the mesoporous TiO 2 film by the layer-by-layer technique using titania nanoparticles as cations and sodium sulfonated polystyrene, PSS, as a polyanion. The TiO 2/PSS blocking layer in a DSC prevents the physical contact of FTO and the electrolyte and leads to a 28% increase in the cell's overall conversion efficiency, from 5.7% to 7.3%.

“Brick and Mortar” Strategy for the Formation of Highly Crystalline Mesoporous Titania Films from Nanocrystalline Building Blocks

We present a novel “brick and mortar” strategy for creating highly efficient transparent TiO2 coatings for photocatalytic and photovoltaic applications. Our approach is based on the fusion of preformed titania nanocrystalline “bricks” through surfactant-templated sol−gel titania “mortar”, which acts as a structure-directing matrix and as a chemical glue. The similar chemical composition of both bricks and mortar leads to a striking synergy in the interaction of crystalline and amorphous components, such that crystallization is enhanced upon thermal treatment and highly porous and highly crystalline structures are formed at very mild conditions. Coatings with a broad variety of periodic mesostructures and thicknesses ranging from few nanometers to several micrometers are accessible using the same organic template, and the final structures are tunable by varying the fraction of the “bricks”. The beneficial combination of crystallinity and porosity leads to greatly enhanced activity of the films in photocatalytic processes, such as the photooxidation of NO. Acting as the active layers in dye-sensitized solar cells, films of only 2.7 μm in thickness exhibit a conversion efficiency of 6.0%.

Structure and thermal properties of transparent conductive nanoporous F:SnO 2 films

The nanoporous F:SnO 2 materials prepared for the purpose of dye-sensitized solar cells (DSCs) application are composed of SnCl 4 (98.0%) and HF (48–51%), produce with a NH 4OH aqueous solution with sol–gel method as a catalyst. Acetylene black is needed to make nano-porous from FTO heated until 120 °C that will change it from sol to gel and with that 2 phase sintering with 500 °C and 550 °C can be predicted to produce nano-materials. The preferred orientation indicates (110), (101), (211) for SnO 2 and (200) for fluorine, respectively. The main IR features include resonances at 660, 620 and 540 cm − 1 . From the FE-SEM results, the mean pore size of the sample is range of 16–38 nm. Finally, the nanoporous F:SnO 2 film used for TCO layer of dye-sensitized solar cells (DSCs) exhibited an energy conversion efficiency of about 1.83% at light intensity of 100 mW/cm 2.

Synthesis of Amorphous Er3+-Yb3+Co-doped TiO2and Its Application as a Scattering Layer for Dye-sensitized Solar Cells

, (ii) inefficient light absorption by dyes in the near infra-red region, (iii) sub-optimum photo-voltage output, (iv) resistance losses, (v) light intensity de-pendant recombination, (vi) and non-ideal diode dark currents among others. Efforts have led to maximum power con-version under full sunlight to about 10% for a cell with an ac-tive area of 0.25 cm

Coupling of Titania Inverse Opals to Nanocrystalline Titania Layers in Dye-Sensitized Solar Cells

We report a quantitative comparison of the photoaction spectra, short circuit current densities, and power conversion efficiencies of dye-sensitized solar cells (DSSCs) that contain bilayers of nanocrystalline TiO2 (nc-TiO2) and titania inverse opal photonic crystals (PCs). Cells were fabricated with PC/nc-TiO2 and nc-TiO2/PC bilayer films on glass/tin oxide anode of the cell, as well as in a split configuration in which the nc-TiO2 and PC layers were deposited on the anode and cathode sides of the cell, respectively. Incident photon current efficiencies at single wavelengths and current-voltage curves in white light were obtained with both cathode and anode side illumination. The results obtained support a model proposed by Miguez and co-workers, in which coupling of the low refractive index PC layer to the higher index nc-TiO2 layer creates a standing wave in the nc-TiO2 layer, enhancing the response of the DSSC in the red region of the spectrum. This enhancement is very sensitive to the degree of physical contact between the two layers. A gap on the order of 200 nm thick, created by a polymer templating technique, is sufficient to decouple the two layers optically. The coupling of the nc-TiO2 and PC layers across the gap could be improved slightly by treatment with TiCl4 vapor. In the bilayer configuration, there is an enhancement in the IPCE across the visible spectrum, which is primarily caused by defect scattering in the PC layer. There is also an increase of 20-50 mV in the open circuit photovoltage of the cell. With anode side illumination, the addition of a PC layer to the nc-TiO2 layer increased the efficiency of DSSCs from 6.5 to 8.3% at a constant N719 dye loading of 155-160 nmol/cm2.

Electrophoretically Deposited TiO2 Nanotube Light-Scattering Layers of Dye-Sensitized Solar Cells

We report herein the enhanced light-to-electricity conversion efficiency of a dye-sensitized solar cell using a new bilayer structure of the TiO2 electrode. The bilayer structure consists of a light-absorbing TiO2 nanoparticle layer together with a light-scattering TiO2 nanotube layer formed upon. High aspect-ratio TiO2 nanotubes (α-TNTs) with a diameter of 20 nm were prepared via anodization of a Ti sheet in a perchloric acid solution, and the α-TNT layer was electrophoretically deposited onto the sintered TiO2 nanoparticle layer. The light-scattering property of the α-TNT layer was comparable to that of the commonly used TiO2 sub-micron nanoparticle layer. The α-TNT layer provided a large surface area for dye-adsorption as well as an efficient transport pathway for photo-generated carriers. These effects allowed a higher incident photon-to-current efficiency of the bilayer TiO2 structure with the nanotube light-scattering layer over the whole spectral range relative to that with a sub-micron nanoparticle layer.

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.

Anchoring Cadmium Chalcogenide Quantum Dots (QDs) onto Stable Oxide Semiconductors for QD Sensitized Solar Cells

Anchoring quantum dots (QDs) onto thermodynamically stable, large band gap oxide semiconductors is a very important strategy to enhance their quantum yields for solar energy conversion in both visible and near-IR regions. We describe a general procedure for anchoring a few chalcogenide QDs onto the titanium oxide layer. To anchor the colloidal QDs onto a mesoporous TiO2 layer, linker molecules containing both carboxylate and thiol functional groups were initially attached to TiO2 layers and subsequently used to capture dispersed QDs with the thiol group. Employing the procedure, we exploited cadmium selenide (CdSe) and cadmium telluride (CdTe) quantum dots (QDs) as inorganic sensitizers for a large band gap TiO2 layer of dye-sensitized solar cells (DSSCs). Their attachment was confirmed by naked eyes, absorption spectra, and photovoltaic effects. A few QD-TiO2 systems thus obtained have been characterized for photoelectrochemical solar energy conversion.

The Electronic Role of the TiO2 Light-Scattering Layer in Dye-Sensitized Solar Cells

Dye-sensitized solar cells have been fabricated with different kinds of TiO2 films including SiO2 coated and bare TiO2 microparticles as light-scattering layer (LSL). Results show that the LSL barely affects the cell's dark current, whereas under illumination, it made a significant contribution to the total photocurrent. Photo-voltage decay measurements performed under bias illumination show the density of electronic states (DOS) of the LSL to be two times smaller than that of a transparent nanoparticle layer (TNL). Strikingly, DSCs fabricated from a 4.5μm thick LSL alone showed a conversion efficiency of 5% despite of being pale pink in color. This impressive performance is attributed to light containment in the LSL and a low density of defect electronic states.

Fabrication of TCO Layer for Dye-Sensitized Solar Cells by Spray Pyrolysis Deposition Technique

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