Nanoporous TiO2 Layer Research Articles

In situ formation of ZnO scattering sites within a TiO2 nanoparticles film for improved dye-sensitized solar cells performance

Abstract A ZnO/TiO 2 composite layer was fabricated on top of a nanoporous TiO 2 layer to form a heterostructure bilayer photoanode (P-PZ). The in-situ scattering sites of ZnO were formed inside the assembled photoanode (P-PZ) through the dissolution of ZnO particles caused by soaking in titanium tetrachloride solution. In comparison, the conventional TiO 2 photoanodes (2P) and photoanodes with incorporation of the commercial large TiO 2 particles (P-PT) were also prepared, and the three photoanodes (2P, P-PT, P-PZ) were all with the thickness of about 14.2 μm. A light-to-electricity conversion efficiency ( η ) of 7.50% was received for the P-PZ-based DSSCs, much higher than that of the DSSCs with 2P (5.34%) and P-PT (5.96%) photoanodes. The superior performance of the DSSC with P-PZ photoanode is mainly attributed to the following factors. (i) The in-situ scattering sites exhibit great light scattering ability, resulting in the great improvement in the short-circuit current density ( J sc ). (ii) The ZnO-coated TiO 2 structure shifts the conduction band of TiO 2 , leading to the great increase in the open circuit voltage ( V oc ).

A comparative study on the photocatalytic activities of microporous and nanoporous TiO2 layers prepared by electrochemical anodization

Abstract In this paper, we present results of comparative studies on the photocatalytic activity of microporous and nanoporous titanium dioxide (TiO 2 ) layers formed on titanium substrates by electrochemical anodization at different voltages. Two sample groups each including four samples was prepared for microporous and nanoporous TiO 2 layer formation. Microporous TiO 2 layers were prepared in 1 M H 2 SO 4 solution in 10 min. Nanoporous TiO 2 layers were formed in %1 HF solution in 30 min and then annealed at 480 °C in ambient air. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The photocatalytic activity of the samples was determined by assessing the decomposition rate of methylene blue (MB) solutions under UV light for different periods of time. By using the data obtained from the UV-Visible spectrophotometer, photocatalytic decomposition kinetics was also determined. The results indicated that nanoporous TiO 2 layers formed by applying 20 V showed optimal photocatalytic performance, whereas the sample anodized at 250 V exhibited the highest photocatalytic activity within its own sample group, nearly matching the photocatalytic activity of the highest performing sample.

Improving the performance of dye-sensitized solar cells by using the conversion luminescence of a phosphor

Dye-sensitized solar cells (DSSCs) have been intensively studied since their discovery in 1991. A DSSC is composed of an electrode made of a dye-adsorbed nanoporous TiO2 layer on a fluorine-doped tin-oxide (FTO) glass substrate, redox electrolytes, and a counter electrode. One of the ways to increase the efficiency of DSSC is to enhance the harvest of light. Many synthetic dyes have been synthesized and employed to improve the harvest of light and increase photocurrent production by DSSCs; however, even the best dyes (e.g., N-719) only absorb in the wavelength range of 400–800 nm, and most ultraviolet wavelengths are not used. In this work, phosphor is introduced to the TiO2 photoelectrode of a DSSC to improve the light harvesting, photovoltage, photocurrent production, and solar conversion efficiency by using a conversion-luminescence process. Moreover, further increases in the conversion efficiency of the DSSC are possible.

Enhancing Photoelectrical Performance of Dye-Sensitized Solar Cell Using Phosphor Photoelectrode

Dye-sensitized solar cells (DSSCs) are composed of an electrode made of a dye-adsorbed nanoporous TiO2 layer on a fluorine-doped tin oxide (FTO) glass substrate, redox electrolytes, and a counter electrode. In this study, phosphor is introduced into the TiO2-layer electrode in a DSSC. By a conversion luminescence, YAG:Ce3+ phosphor improves light harvesting and increases the photocurrent production. Using a TiO2 electrode containing 5.00 wt% mixed YAG:Ce3+, the light-to-electric energy conversion efficiency of the DSSC reaches 6.24%, which is higher by a factor of 1.52 than that of a DSSC without YAG:Ce3+.

The Effect of Phosphor-TiO2 Layer on the Performance of Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are composed of an electrode made of a dye-adsorbed nanoporous TiO2 layer on a fluorine-doped tin oxide (FTO) glass substrate, redox electrolytes, and a counter electrode. In this study, phosphor is introduced into the TiO2-layer electrode of a DSSC. The admixed phosphor content in the TiO2 paste is varied from 1.0 to 10.0 wt%. By a conversion-luminescence process, ZnGa2O4:Mn2+ phosphor improves light harvesting and increases the photocurrent. The phosphor elevates both, the energy level of electrons in the oxide film and Voc of the DSSC. Using a TiO2 electrode containing 5.00 wt% of admixed ZnGa2O4:Mn2+, the light-to-electricity energy-conversion efficiency of the DSSC reaches 8.02%, which is higher by a factor of 1.25 than that of a DSSC without ZnGa2O4:Mn2+.

Efficiency enhancement of dye-sensitized solar cells by interface modification between photoanode and electrolyte.

A nanoporous TiO2 layer on a transparent electrode was modified with an aqueous lithium hydroxide solution by a simple dipping process, and effects of the modified electrode on the photovoltaic properties of dye-sensitized solar cells were investigated. The modification led to a considerable improvement of 23.6% in power conversion efficiency due to an increase in both open circuit voltage and fill factor. From the measurements of the electronic band structure, electrochemical impedance spectra and incident photon-to-current conversion efficiency, it was revealed that the modification by LiOH formed a surface dipole on the TiO2 electrode, leading to a negative shift of conduction band edge of TiO2.

Diffusion length in nanoporous TiO2 films under above-band-gap illumination

We determined the carrier diffusion lengths in TiO2 nanoporous layers of dye-sensitized solar cells by using scanning photocurrent microscopy using an ultraviolet laser. Here, we excited the carrier directly in the nanoporous layers where the diffusion lengths were found to 140 μm as compared to that of visible illumination measured at 90 μm. The diffusion length decreased with increasing laser modulation frequency, in which we determined the electron lifetimes and the diffusion coefficients for both visible and UV illuminations. The diffusion lengths have been studied in terms of the sintering temperatures for both cells with and without binding molecules. We found a strong correlation between the diffusion length and the overall light-to-current conversion efficiency, proving that improving the diffusion length and hence the interparticle connections, is key to improving cell efficiency.

Increasing the tribological performances of Ti–6Al–4V alloy by forming a thin nanoporous TiO2 layer and hydroxyapatite electrodeposition under lubricated conditions

In this study, comparative investigation of (i) untreated Ti–6Al–4V alloy, (ii) nanoporous thin TiO 2 layer formed by controlled anodic oxidation and (iii) electrodeposited hydroxyapatite coatings into porous oxide layer was carried out for evaluation of sliding-wear performances in a bio-simulated environment. Wear mechanisms, wear volumes and friction coefficients of the three types of surfaces under lubricated conditions in a bio-simulated solution were recorded and analyzed. The results presented herein show that, under the investigated tribocorrosion conditions (under reciprocating sliding), both surface treatments applied have improved the wear resistance and friction coefficients as compared to the untreated Ti–6Al–4V alloy surface. • Nanoporous TiO 2 film and electrodeposited HA reduce the friction coefficient of the untreated alloy. • Electrochemically modified surfaces reduce the size and depth of the wear tracks. • Shallower and narrower wear tracks were seen on treated surfaces than that of untreated ones. • Both electrochemically surface modifications decrease the wear volume loss and wear depth.

Nano-porous TiO2 layer using ultrafine nano-particles for the blocking layer in dye-sensitized solar cells.

A nano-porous TiO2 layer was produced by spray-deposition using ultrafine anatase nano-particles for the blocking layer for the dye-sensitized solar cells (DSCs). The microstructure and the electrochemical properties of the spray-deposited TiO2 layer were examined. The results of electrochemical properties showed that the spray-deposited TiO2 layer was capable to suppress the I3- ions diffusion to FTO substrate, reducing the electron recombination between the electrons on FTO substrate and I3- ions in electrolyte. In addition, the connection between TiO2 film and FTO substrate was improved by the TiO2 layer. Therefore, the short circuit current density and thereby the photo-to-electric energy conversion efficiency were improved by this blocking layer. The blocking effect of the porous layer was attributed to both the complicated pore structure of the spray-deposited layer and the enhanced connections between TiO2 film and FTO substrate. The low temperature characteristic of spray deposition approach indicates that it is suitable to the flexible-based DSCs.

The effect of anodization parameters on the formation of nanoporous TiO2 layers and their photocatalytic activities

In this work, nanoporous titanium dioxide (TiO2) layers were successfully formed by electrochemical anodization method on titanium (Ti) surface in fluorine containing electrolytes with different processing parameters. The effects of anodization voltages, electrolyte temperature and anodization time on the microstructure and photocatalytic performance of nanoporous TiO2 layers were investigated and compared in details. Nanoporous structures were annealed at 480 °C for 2 h in air in order to obtain anatase transformation and increase crystallinity. The phase structure and surface morphology of the samples characterized by means of X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. The photocatalytic activity tests of the samples were evaluated by the degradation of aqueous methylene blue (MB) solutions under UV light illumination for different periods of time. The results showed that the processing parameters on production of nanoporous TiO2 layers played important roles in the degradation of aqueous MB solutions. To sum up, the highest photocatalytical activity was obtained at the sample anodized under 30 V for 30 min at 20 °C among the samples.

TiO2 and Al2O3 nanoporous oxide layers decorated with silver nanoparticles—active substrates for SERS measurements

Self-organized nanoporous oxide layers (TiO2, Al2O3) exhibiting specific properties, obtained by anodic oxidation at a constant voltage in neutral electrolyte, may serve as attractive SERS substrates for investigating the interactions between an adsorbate and adsorbent, or as a stable platform for detecting various organic compounds. This paper presents the influence of the size of the nanotubes/nanopores and the structure of the porous oxide layers on the SERS enhancement factor, E F. We used pyridine and mercaptobenzoic acid as probe molecules, since they have a large cross-section for Raman scattering. To characterize the morphology and structure of the oxide layer substrates, before and after vacuum vapor deposition of silver nanoparticles, we applied scanning electron microscopy, X-ray diffraction and surface analytical techniques: AES, XPS and SERS. The results obtained show that for the same amount of Ag (0.02 mg/cm2) the size of the nanopores significantly affects the E F, which reaches, at a properly chosen nanopore size, distinctly higher values than that characteristic of a standard silver surface roughened by electrochemical cycling, i.e. E F > 106. The new Ag/MeO x –NT composites layer, ensure a good reproducibility of the SERS measurements and exhibit stability over a limited period of time.

Self-Assembled All-Conjugated Block Copolymer as an Effective Hole Conductor for Solid-State Dye-Sensitized Solar Cells

An all-conjugated diblock copolymer, poly(2,5-dihexyloxy-p-phenylene)-b-poly(3-hexylthiophene) (PPP-b-P3HT), was synthesized and applied as a hole transport material (HTM) for the fabrication of solid-state dye-sensitized solar cells (ss-DSCs). This copolymer is characterized by an enhanced crystallinity, enabling its P3HT component to self-organize into interpenetrated and long-range-ordered crystalline fibrils upon spin-drying and ultimately endowing itself to have a faster hole mobility than that of the parent P3HT homopolymer. Transient photovoltage measurements indicate that the photovoltaic cell based on PPP-b-P3HT as the HTM has a longer electron lifetime than that of the reference device based on P3HT homopolymer. Moreover, comparing the two ss-DSCs in terms of the electrochemical impedance spectra reveals that the electron density in the TiO2 conduction band is substantially higher in the PPP-b-P3HT device than in the P3HT cell. Above observations suggest that the PPP block facilitates an intimate contact between the copolymer and dye molecules absorbed on the nanoporous TiO2 layer, which significantly enhances the performance of the resulting device. Consequently, the PPP-b-P3HT ss-DSC exhibits a promising power conversion efficiency of 4.65%. This study demonstrates that conjugated block copolymers can function as superior HTMs of highly efficient ss-DSCs.

Effect of Photoelectrode with Phosphor-Containing TiO2 Layer for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are composed of a dye-adsorbed nanoporous TiO2 layer on a fluorine-doped tin oxide (FTO) glass substrate, redox electrolytes, and a counter electrode. The phosphor is introduced into the TiO2 layer electrode in a DSSC. The content of phosphor-containing in the TiO2 paste is varied from 0.25 to 5.00 wt %. The synthesized TiO2 paste is deposited on FTO glass using a doctor blade. The conversion luminescence process of phosphor, increases both the light harvesting efficiency and the photocurrent. Using the 0.5 wt % Ba3Si6O12N2:Eu2+-containing TiO2 electrode, the light-to-electric-energy conversion efficiency of the DSSCs reaches 4.61% under simulated solar light irradiation at 100 mW/cm-2, which is an increase by a factor of 1.41 compared with that of the DSSCs without Ba3Si6O12N2:Eu2+.

Preparation of doping metal TiO2 particle/nanotube composite layer and their applications in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) are composed of a dye-adsorbed nanoporous TiO2 layer on a fluorinedoped tin oxide (FTO) glass substrate, redox electrolytes, and a counter electrode. DSSCs are constructed through the application of nano-metals and TiO2 nanoparticle/TiO2 nanotube (TNT) composite particles with various compositions. The use of oxide semiconductors in the form of nanorods, nanowires, and nanotubes is an interesting approach to improve electron transport through the film. In addition, a suitable amount of TNT in the film could provide a large surface area for the adsorption of the dye. A nano-metal is proposed, wherein the conduction band (CB) prohibits the trapping effects of electrons within the TiO2 conduction band. This result is attributed to the prevention of electron recombination between the electrons in the TiO2 conduction band with dye or electrolytes. A TiO2 composite layer was coated onto FTO glass using a screen-printing method. The dye-sensitized solar cells were fabricated using N719 ruthenium (II) dye and I3/I3− electrolyte. The impedance results indicate improved electron transport at the TiO2/dye/electrolyte interface. The DSSC based on the Fe2O3/TiO2/TNT composite particle hybrids exhibits better photovoltaic performance than the cell made from only TiO2 nanoparticles.

Effects of TiO2 electron blocking layer on photovoltaic performance of photo-electrochemical cell

Abstract Dye-sensitized solar cells (DSCs) have used transparent conductive Fluorine-doped SnO2 (FTO) glass/porous TiO2 layer attached using dye molecules/electrolytes (I−/I3−)/Platinium-coated FTO glass configuration. In this work, prior to the coating of nanoporous TiO2 layer on FTO glass, a dense layer of TiO2 film with a thickness of less than ∼100 nm was deposited directly onto the FTO as an electron blocking layer by radio frequency (RF) magnetron sputtering. Under 100 mW/cm2 illumination at AM 1.5, the energy conversion efficiency (η) of the prepared DSC with electron blocking layer of 80 nm thickness was 6.9% (Voc = 0.67 V, Jsc = 12.18 mA/cm2, ff = 0.63), which is increased by 1.3% compared to the typical cell without electron blocking layer.

Growth and properties of Ti films formed by dc magnetron sputtering for TCO-free photo electrode applications

Porous Titanium (Ti) films were fabricated using dc magnetron sputtering (DMS) technique on a nanoporous TiO2 layer prepared by sol-gel combustion (SGC) method; films were investigated with respect to their photoanode properties of TCO-free DSCs. The sheet resistivity of porous Ti films was enhanced with substrate temperatures increasing in the range of 150°C–300°C. The porous Ti layer of 8.5 µm thickness deposited at substrate temperature of 250°C has a lower sheet resistivity (∼1.9 Ω/sq.) compared to that of FTO. The porous Ti layer, with highly ordered columnar structure prepared by 5 mTorr sputtering at substrate temperature of 250°C, shows good impedance and conversion efficiency (FF: 0.68, Voc: 0.69V, Jsc: 11.47 mA/cm2, η: 5.38%).

Creation of nanoporous TiO2surface onto polyetheretherketone for effective immobilization and delivery of bone morphogenetic protein

This study evaluated the utility of the creation of a nanoporous TiO2 surface to enhance the in vitro biocompatibility and in vivo osseoconductivity of polyetheretherketone (PEEK) implants by providing favorable sites for the effective immobilization of bone morphogenetic protein-2 (BMP-2). A uniform nanoporous TiO2 layer with a pore diameter of ∼70 nm was successfully created by anodizing a Ti film, which had been deposited onto a PEEK substrate via electron beam (e-beam) evaporation technique. This nanoporous, hydrophilic TiO2 surface enabled the efficient immobilization of BMP-2, resulting in a remarkable enhancement in in vitro biocompatibility that was assessed in terms of cell attachment, proliferation, and differentiation. The in vivo animal tests also confirmed that the nanoporous TiO2 surface immobilized with BMP-2 could significantly enhance the osseoconductivity of PEEK implants. The BMP-immobilized PEEK implant with the nanoporous TiO2 surface showed much higher bone-to-implant contact (BIC) ratio (60%) than the bare PEEK (30%), PEEK with the nanoporous TiO2 surface (50%) and even BMP-immobilized PEEK without the nanoporous TiO2 surface (32%).

Study of the Anchoring Process of Tethered Unsymmetrical Zn-Phthalocyanines on TiO2 Nanostructured Thin Films

Thin nanoporous TiO2 layers, deposited by dc reactive sputtering, have been functionalized with a novel unsymmetrical Zn(II) phthalocyanine (ZnPc-II) bearing a push–pull system, properly designed for application in dye sensitized solar cells. The anchoring process has been studied by combining visible absorption (vis), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) in order to investigate the molecular assembly during the early stage of the sensitizing process. The vis and XPS measurements indicate that the ZnPc-II surface density (dsurf, molecules/cm2) and its binding geometry are strongly affected by the concentration of the grafting solutions. It has been observed that the ZnPc-II surface density monotonically increases by increasing the solution concentration up to a saturation of dsurf ∼ 1.0 × 1013 molecules/cm2. Angle resolved XPS analyses indicate that at low molecular surface density a strong interaction between the ZnPc-II aromatic macrocycle and the TiO2 surface occurs...

Cost-effective nanoporous SiO2–TiO2 coatings on glass substrates with antireflective and self-cleaning properties

Simultaneous antireflective and self-cleaning properties have been realized by depositing double-layered SiO2–TiO2 coatings onto glass substrates using a combined sol–gel dip-coating process in which the two oxide layers were deposited in succession. The first layer is composed of a hybrid methyl-functionalized nanoporous SiO2 material that provides on average a 6% anti-reflection gain. The degree of antireflectivity can be controlled by adjusting the thickness and refractive index by selecting suitable solvents and pore-forming agents in the coating mixture. The second layer is an ultrathin TiO2 nanoporous layer deposited on top of antireflective layer. The high hardness of the TiO2 top layer acts as a protection barrier toward mechanical damage and ensures the surface is self-cleaning. An average anti-reflectivity of 3.4% achieved over a spectrum range of 400–800 nm for the optimal SiO2–TiO2 bilayers is obtained. It is found that a homogeneous pore size distribution in the SiO2 layer introduced by using isopropanol as the solvent can compensate for the TiO2 band edge absorption based on the optical interference that occurs between the two layers. These systems are easy to produce on a large scale at low cost and exhibit high mechanical and chemical durability. These materials are thus suitable for use as bifunctional antireflective and self-cleaning coatings for use as large substrates for solar cells.

Preparation of nanoporous TiO2 films for DSSC application by a rapid atmospheric pressure plasma jet sintering process

Abstract We investigate the nanoporous TiO 2 films sintered by atmospheric pressure plasma jets (APPJs) and their applications as photoanodes of dye-sensitized solar cells (DSSCs). A 30-s APPJ-sintered nanoporous TiO 2 layer exhibits an additional absorption band between 400 and 500 nm in wavelength, attributed to incomplete removal of the organic solvents in the pastes. For TiO 2 layers sintered by APPJs for 60 s and beyond, the absorption spectra are nearly identical to those of a conventional 15 min, 510 °C calcined sample. The XRD and XPS results indicate similar characteristics for APPJ-sintered and furnace-sintered TiO 2 films. A DSSC with a 30-s APPJ-sintered TiO 2 photoanode shows poor cell efficiency with an extremely large TiO 2 /dye/electrolyte electron transport interfacial resistance and a short carrier lifetime. As the APPJ treatment time reaches 60 s and beyond, the power conversion efficiencies become comparable to that of a sample with a 510 °C conventionally calcined TiO 2 photoanode. Our experimental results verify that a 60-s APPJ sintering process is sufficient to replace a conventional 15 min, 510 °C furnace calcination process for TiO 2 photoanodes of DSSCs. The ultra-short sintering process is made possible by the synergistic effect of the temperature and the reactivity of the APPJ, which can lower the fabrication cost.