Photovoltaic efficiency on dye-sensitized solar cells (DSSC) assembled using Ga-incorporated TiO2 materials

This study examined the photoelectric conversion efficiency of DSSC (dye-sensitized solar cell) when nanometer sized Ga (0.25, 0.50, and 1.00 mol%)–TiO₂ prepared using a hydrothermal method was employed as a working electrode material. The particle sizes observed in the transmission electron microscopy images were <20 nm in all samples. However, with increasing Ga concentration, the size increased and the shapes transformed to a stick form. The absorption band was slightly blue-shifted upon the incorporation of gallium ions, but the intensity of the photoluminescence (PL) curves of the Ga-incorporated TiO₂ was significantly smaller, with the smallest case being the 0.50 mol% Ga–TiO_2, which was related to recombination between the excited electrons and holes. When Ga–TiO₂ was applied in DSSC, the energy conversion efficiency was enhanced considerably compared to that using pure TiO₂; it was approximately 4.57% with the N3 dye under 100 mW/cm² of simulated sunlight. These results are in agreement with an electrostatic force microscopy (EFM) study showing that the electrons were transferred rapidly to the surface of Ga–TiO₂ film, compared with that on a pure TiO₂ film.     

Synthesis and characterisation of thin-film TiO2 dye-sensitised solar cell

A TiO₂ dye-sensitised solar cell (DSSC) is fabricated and characterised using: X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), electron diffraction X-ray (EDX) analysis, UV–vis spectrometry and a current?voltage (I?V) test. Thicker anatase TiO₂ gives rise to better crystallinity and subsequently leads to better cell efficiency. Mesoporous TiO₂ with a suitable, average pore size results in higher conversion efficiency. Smaller particle sizes lead to higher dye uptake and increase short circuit current density, J_sc. Addition of scattering layer and/or dual TiCl₄ treatment for DSSCs having optimum thickness enhanced their performance. A DSSC having double TiO₂ layers (20 nm+50 nm) with dual TiCl₄ treatment achieved the highest conversion efficiency of 9.78%.     

Preparation of dye sensitized solar cell by using supercritical carbon dioxide drying

Dye-sensitized solar cells (DSSC) derived from TiO₂ aerogel film electrodes were fabricated. TiO₂ aerogels were obtained by using sol–gel method and supercritical carbon dioxide (sc-CO₂) drying. First, TiO₂ wet gels were obtained by sol-gel method. Then, the solvents in the TiO₂ wet gels were replaced by acetone. The TiO₂ aerogels were obtained by using sc-CO₂ drying from the TiO₂ wet gels. The conditions of sc-CO₂ drying were at 313, 323 K and 7.8–15.5 MPa. The electrodes with TiO₂ aerogel films were obtained by deposition of the aerogels on glass substrates. The electrodes with TiO₂ aerogel films and a commercial particle film of various thickness were obtained by repetitive coatings and calcinations. The amount of dye adsorbed on the TiO₂ films with sc-CO₂ drying was higher than that of commercial particle film. The amount of dye adsorbed on the TiO₂ films increased with increasing surface area of the TiO₂ film. DSSCs were assembled by using the TiO₂ aerogel film electrodes and their current–voltage performance was measured. The power performance of DSSC made by supercritical drying was higher than that of commercial particles. The DSSC with the film electrode made at 313 K and 15.5 MPa showed the best power performance (J_sc = 7.30 mA/cm², V_oc = 772 mV, η = 3.28%).     

Comparison of the photovoltaic efficiency on DSSC for nanometer sized TiO2 using a conventional sol–gel and solvothermal methods

When the two types of TiO₂ coatings prepared by sol–gel and solvothermal methods were applied to dye-sensitized solar cell (DSSC) in this study, the energy conversion efficiency of the solvothermal-modified TiO₂ was considerably higher than that on the sol–gel modified TiO₂; approximately 8.51 (solvothermal) and 5.93% (sol–gel) with the N719 dye under 100 mW/cm² of simulated sunlight, respectively. These results are in agreement with an electrostatic force microscopy (EFM) study showing that the electrons were transferred rapidly to the surface of the solvothermal-modified TiO₂ film, compared with that on a sol–gel modified TiO₂ film. Furthermore, FT-IR analysis of the films after N719 dye adsorption showed that the solvothermal-modified TiO₂ had a strong band at 500 cm^?1, which was assigned to metal–O, due to a new Ti–O bond between the O of COO^? and a Ti atom. This peak was considerably weaker in the sol–gel modified TiO₂.     

Facile assembly of TiO2 nanospheres/SnO2 quantum dots composites with excellent photocatalyst activity for the degradation of methyl orange

In this report, SnO₂ quantum dots anchored on TiO₂ nanospheres (TiO₂/SnO₂ composites) have been synthesized by a simple one-step hydrothermal process, and then employed as photocatalyst in photodegradation system. The microstructure of TiO₂/SnO₂ composites reveals that the SnO₂ quantum dots are dispersed on the surface of TiO₂ nanospheres uniformly. The photocatalytic behavior of the as-prepared samples revealed that the composites exhibited highly efficient performance by degrading 100 mL of 10 mg/L methylene orange in 15 min completely under ultraviolet-visible light. Owning to the special structure of the composites, TiO₂/SnO₂ shows a more UV–vis light absorption than either pure TiO₂ nanospheres or pure SnO₂ quantum dots. This study offers a facile method to prepare TiO₂/SnO₂ composites, which will be a choice for greatly extending potential applications in water pollution treatment, degradation of pollutants and other related fields.     

Preparation of ZnO-coated TiO2 electrodes using dip coating and their applications in dye-sensitized solar cells

This study investigates the applicability of a ZnO-coated TiO₂ working electrode in a dye-sensitized solar cell (DSSC). This working electrode was designed and fabricated by the following procedures: (1) two consecutive TiCl₄ treatments were performed when preparing the TiO₂ electrode, one prior to and the other following the spin printing of the TiO₂ colloid on a FTO-glass (Fluorine doped tin oxide, SnO₂:F) substrate; (2) a simple dip coating method was used to fabricate a ZnO-coated TiO₂ electrode by immersing a FTO-glass substrate with a TiO₂ film in a solution of zinc acetate dehydrate [Zn(CH₃COO)₂?2H₂O] and ethanol. This working electrode was then immersed in a solution of N-719 (Ruthenium) dye at a temperature of 70 °C for a preset duration. Finally, the DSSC was assembled, and the short-circuit photocurrent, the open-circuit photovoltage, and the power conversion efficiency of DSSC were measured using an I–V measurement system. The effects of the concentration of Zn(CH₃COO)₂?2H₂O, the duration of dipping, and the dye loading on the power conversion efficiency of a DSSC were also examined. Most importantly, this study shows that the power conversion efficiency of the DSSC with a ZnO-coated TiO₂ electrode (6.62%) substantially exceeds that of the conventional DSSC with a TiO₂ electrode (5.45%) due to the effects of a ZnO barrier and the TiCl₄ treatment.     

All-solid-state quantum-dot-sensitized solar cells with compact PbS quantum-dot thin films and TiO2 nanorod arrays

To improve the electron injection efficiency from PbS quantum dots to TiO₂ nanorods and prevent the direct contact of spiro-OMeTAD and TiO₂ nanorods, a compact PbS quantum-dot thin film can be successfully obtained on TiO₂ nanorod arrays 360 nm in length by repeated spin coating of Pb(Ac)₂, Na₂S and 1,2-ethanedithiol solution in a step-by-step process. The corresponding solid-state quantum-dot-sensitized solar cells are fabricated using a novel structured FTO/compact PbS quantum-dot thin film sensitized TiO₂ nanorod array/spiro-OMeTAD/Au that achieves a photoelectric conversion efficiency of 3.57% under AM 1.5 G illumination (100 mW cm⁻²), which represents a high value among all-solid-state PbS quantum-dot-sensitized TiO₂ nanorod array solar cells.     

Synthesis of TiO2(B)/SnO2 composite materials as an anode for lithium-ion batteries

A TiO₂(B) nanosheets/SnO₂ nanoparticles composite was prepared by the hydrothermal and chemical bath deposition (CBD) methods, and its electrochemical properties were investigated for use as the anode material of a lithium-ion battery. The as-prepared composites consisted of monoclinic-phase TiO₂(B) nanosheets and cassiterite structure SnO₂ nanoparticles, in which SnO₂ nanoparticles were uniformly decorated on the TiO₂(B) nanosheets. The TiO₂(B)/SnO₂ composites showed a higher reversible capacity and better durability than that of the pure TiO₂(B) for use as a battery anode. The composite electrodes exhibiting a high initial discharge capacity of 2239.1 mAh g⁻¹ and a discharge capacity of more than 868.7 mAh g⁻¹ could be maintained after 50 cycles at 0.1 C in a voltage range of 1.0–3.0 V at room temperature. The results suggest that TiO₂(B) nanosheets coated with SnO₂ could be suitable for use as a stable anode material for lithium-ion batteries. In addition, the coulombic efficiency of the nanosheets remains at an average of 93.1% for the 3rd–50th cycles.     

A counter electrode of multi-wall carbon nanotubes decorated with tungsten sulfide used in dye-sensitized solar cells

Multi-wall carbon nanotubes decorated with tungsten sulfide (MWCNTs-WS₂) were synthesized by using a hydrothermal method, and used as a low-cost platinum-free counter electrode for dye-sensitized solar cell (DSSC). Cyclic voltammetry and electrochemical impedance spectroscopy characterizations indicate that the counter electrode has a high catalytic activity for the reduction of triiodide to iodide and a low charge transfer resistance at the electrolyte–electrode interface. A DSSC based on this counter electrode achieves a high power conversion efficiency of 6.41% under a simulated solar illumination of 100 mW cm⁻² (AM 1.5). This efficiency is comparable to 6.56% for a DSSC with Pt counter electrode.     

Photocatalytic reduction of CO2 to energy products using Cu–TiO2/ZSM-5 and Co–TiO2/ZSM-5 under low energy irradiation

Copper or cobalt incorporated TiO₂ supported ZSM-5 catalysts were prepared by a sol–gel method, and then were characterized by XRD, BET, XPS and UV–vis diffuse reflectance spectroscopy. Ti^3 + was the main titanium specie in TiO₂/ZSM-5 and Cu–TiO₂/ZSM-5, which will be oxide to Ti^4 + after Co was doped. With the deposition of Cu or Co, the efficiency of the CO₂ conversion to CH₃OH was increased under low energy irradiation. The peak production rate of CH₃OH reached 50.05 and 35.12 μmol g^− 1 h^− 1, respectively. High photo energy efficiency (PEE) and quantum yield (φ) were also reached. The mechanism was discussed in our study.     

A novel TiO2 − xNx/BN composite photocatalyst: Synthesis,characterization and enhanced photocatalytic activity for Rhodamine B degradation under visible light

A novel TiO_2 − xN_x/BN composite photocatalyst was prepared via a facile method using melamine–boron acid adducts (M·2B) and tetrabutyl titanate as reactants. The morphological results confirmed that nitrogen-doped TiO₂ nanoparticles were uniformly coated on the surface of porous BN fibers. A red shift of absorption edge from 400 nm (pure TiO₂) to 520 nm (TiO_2 − xN_x/BN composites) was observed in their UV–Vis light absorption spectra. The TiO_2 − xN_x/BN photocatalysts exhibited enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) and the highest photocatalytic degradation efficiency reached 97.8% under visible light irradiation for 40 min. The mechanism of enhanced photocatalytic activity was finally proposed.     

Sol-gel based TiO2 paste applied in screen-printed dye-sensitized solar cells and modules

A simple manufacturing process based on screen-printing is crucial for a successful commercialization of dye-sensitized solar cells (DSSCs). We developed the sol–gel based TiO₂ paste in such a way that solely a single step deposition is sufficient to realize a sponge-like structure of the layer assuring its high activity in DSSCs. For the first time the sol–gel based TiO₂ paste was screen printed and tested in DSSC masterplates and PV mini-modules. Electroluminescence imaging of the mini-module proved layer homogeneity and no manufacturing defects. The conversion efficiency of the PV mini-module with the active area of 75 cm² reaches 5.7% at STC.     

Direct synthesis of carbon nanofibers on the surface of copper powder

A novel approach to synthesize carbon nanofibers (CNFs) directly on the surface of metal μm-sized particles to evenly disperse the carbon nanomaterials in a composite material was proposed. As a metal matrix, 5–10 μm copper particles were utilized. As a carbon source, C₂H₂, CH₄ and CO were examined. The best conditions were found to be in C₂H₂ (30 cm³/min) and H₂ (260 cm³/min) atmosphere at the temperature of 750 °C. The composites based on copper and CNFs prepared by vacuum hot pressing showed the increase in hardness from 35 to 60 kg/mm² almost retaining pure copper electrical properties.     

Sol–gel hydrothermal synthesis of bismuth–TiO2 nanocubes for dye-sensitized solar cell

Bismuth–TiO₂ nanocubes were synthesized via a facile sol–gel hydrothermal method with titanium tetraisopropoxide as the precursor. The influence of the bismuth on the size, morphology, crystallinity and optical behavior of TiO₂ nanocubes were investigated. The samples were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), field emission scanning electron microscopy (FESEM) and UV–visible spectroscopy (UV–vis). Photovoltaic behavior of dye-sensitized solar cells (DSSCs) fabricated using Bi–TiO₂ nanocubes was studied. The DSSCs had an open-circuit voltage (V_oc) of 590 mV, a short-circuit current density (J_sc) of 7.71 mA/cm², and the conversion efficiency (η) of 2.11% under AM 1.5 illumination, a 77% increment as compared to pure TiO₂ nanocubes.     

Dip-coating on TiO2 foams using a suspension of Pt–TiO2 nanopowder synthesized by laser pyrolysis—preliminary evaluation of the catalytic performances of the resulting composites in deVOC reactions

As an extension of a study to generate ceramic-metal nanosized composites further deposited on ceramic foams, here we describe a new route to prepare Pt–TiO₂ nanopowders of controlled metallic size and their further coating of TiO₂ foams. Their efficiency as catalysts in volatile organic compound elimination (deVOC) reactions was evaluated and compared to those of the corresponding classical unsupported mixed powders.Composite metal/ceramic nanopowders (Pt–TiO₂) were synthesized by laser pyrolysis using organo-metallic precursors. Successive dip-coatings on TiO₂ foams with aqueous slurries of nanodispersed Pt–TiO₂ particles were then achieved. Both foam-supported and unsupported Pt–TiO₂ grains of about 20 nm could be stabilized, confirming no significant particles coalescence after a thermal treatment at 460 °C. Both proved equally efficient catalysts for the total oxidation of methanol, selected as probe deVOC reaction, thereby demonstrating that the dispersion of the nanopowders over the preformed ceramics does not modify their catalytic performances.     

Improved ablation resistance of C–C composites using zirconium diboride and boron carbide

Zirconium diboride and boron carbide particles were used to improve the ablation resistance of carbon–carbon (C–C) composites at high temperature (1500 °C). Our approach combines using a precursor to ZrB₂ and processing them with B₄C particles as filler material within the C–C composite. An oxyacetylene torch test facility was used to determine ablation rates for carbon black, B₄C, and ZrB₂–B₄C filled C–C composites from 800 to 1500 °C. Ablation rates decreased by 30% when C–C composites were filled with a combination of ZrB₂–B₄C particles over carbon black and B₄C filled C–C composites. We also investigated using a sol–gel precursor method as an alternative processing route to incorporate ZrB₂ particles within C–C composites. We successfully converted ZrB₂ particles within C–C composites at relatively low temperatures (1200 °C). Our ablation results suggest that a combination of ZrB₂–B₄C particles is effective in inhibiting the oxidation of C–C composites at temperatures greater than 1500 °C.     

Effect of carbon doping on WO3/TiO2 coupled oxide and its photocatalytic activity on diclofenac degradation

The improved photocatalyst carbon-doped WO₃/TiO₂ mixed oxide was synthesized in this study using the sol–gel method. The catalyst was thoroughly characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy, N₂ adsorption desorption analysis, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic efficiency of the prepared materials was evaluated with respect to the degradation of sodium diclofenac (DCF) in a batch reactor irradiated under simulated solar light. The progress of the degradation process of the drug was evaluated by high-performance liquid chromatography (HPLC), whereas mineralization was monitored by total organic carbon analysis (TOC) and ion chromatography (IC). The results of the photocatalytic evaluation indicated that the modified catalyst with tungsten and carbon (TWC) exhibited higher photocatalytic activity than TiO₂ (T) and WO₃/TiO₂ (TW) in the degradation and mineralization of diclofenac (TWC>TW>T). Complete degradation of diclofenac occurred at 250 kJ m⁻² of accumulated energy, whereas 82.4% mineralization at 400 kJ m⁻² was achieved using the photocatalytic system WO₃/TiO₂-C. The improvement in the photocatalytic activity was attributed to the synergistic effect between carbon and WO₃ incorporated into the TiO₂ structure.     

Synthesis and characterization of mesoporous anatase TiO2 nanostructures via organic acid precursor process for dye-sensitized solar cells applications

Titania (TiO₂) nanoparticles have been synthesized using organic precursor technique. The titania nanoparticles were characterized. The results indicated that the prepared titanium oxalate and citrate precursors were transformed to anatase TiO₂ phase at temperature 400 °C for 2 h. Dye-sensitized solar cells were assembled using the prepared nanocrystalline TiO₂ with large surface area. The specific surface area S_BET was 80.9 and 78.6 m²/g using oxalic and citric acids, respectively. The power efficiency was 3.5 and 2.4%. A brief discussion on the possible reasons behind the low power conversion efficiency observed for these type of solar cells was reported.     

Iron-doped TiO2 nanotubes with high photocatalytic activity under visible light synthesized by an ultrasonic-assisted sol-hydrothermal method

A series of iron-doped anatase TiO₂ nanotubes (Fe/TiO₂ NTs) catalysts with iron concentrations ranging from 0.88 to 7.00 wt% were prepared by an ultrasonic-assisted sol-hydrothermal process. The structures and the properties of the fabricated Fe/TiO₂ NTs were characterized in detail and photocatalytic activity was examined using a reactive brilliant red X-3B aqueous solution as pollutant under visible light. The lengths of the NTs were determined to range from 20 nm to 100 nm. The incorporation of the iron ions (Fe³⁺) into the TiO₂ nanotubes shifted the photon absorbing zone from the ultraviolet (UV) to the visible wavelengths, reducing the band gap energy from 3.2 to 2.75 eV. The photocatalytic activity of the Fe/TiO₂ NTs was 2–4 times higher than the values measured for the pure TiO₂ nanotubes.     

Formation of TiC particle during carbothermal reduction of TiO2

Formation of TiC particle during carbothermal reduction of titanium dioxide (TiO₂) was investigated. The mixture with TiO₂ and carbon resin was reacted at 1500 °C for 0–45 min under flowing Argon atmosphere. The powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The partially reduced TiO₂ particles were conglomerated in the initial stage of the reduction and the size of this conglomerate ranged from 500 to 1000 nm. After the complete reaction between Ti as a reduction product and C, the large conglomerates separated to homogeneous and fine TiC particles with a size of 80 nm.