Tuning the dye aerosol impaction and TiO2 nanoparticle stacking structures for High-Efficiency Dye-Sensitized solar cells

The rapid manufacturing of high-efficiency dye-sensitized solar cells (DSSCs) is limited by the slow dye adsorption on TiO₂ nanoparticles (NPs)-accumulated photoelectrode using conventional dip-coating process. Therefore, we aim to accelerate the adsorption of dyes that are attached on TiO₂ NPs by employing an aerosol impactor. Herein the aerosolized dyes are designed to get deposited rapidly on the TiO₂ NPs-accumulated photoelectrode. In addition, to effectively trap the irradiated sunlight in DSSCs, we assemble the photoelectrodes incorporated with bilayered TiO₂ thin films comprising small TiO₂ NPs-based underlayer and large TiO₂ NPs-based overlayer as dye-supporting and light-scattering mediums, respectively. Furthermore, the effects of dye aerosol impaction and TiO₂ stacking structures on the efficiency of DSSCs are examined. The power conversion efficiency (PCE) of DSSCs comprising a N719 dye-supporting layer treated with dip-coating process was determined as ～ 5.67%; however, when the bilayered TiO₂ thin films with an optimized thickness ratio of light-scattering overlayer and dye-supporting underlayer were coated with N719 dyes using dye aerosol impactor, the resulting PCE increased to ～ 7.46%. This suggests that the photovoltaic characteristics of DSSCs can be enhanced considerably using the effective TiO₂ NP stacking structures coated with rapid, uniform, and strong aerosol dye adsorption throughout the TiO₂-based photoelectrodes.     

Preparation of TiO2/NiO composite particles and their applications in dye-sensitized solar cells

This study investigates the applicability of n-type TiO₂ and p-type NiO on the FTO-glass (Fluorine doped tin oxide, SnO₂:F) substrate of the working electrode in a dye-sensitized solar cell (DSSC). The working electrode was designed and fabricated by depositing a film of TiO₂/NiO composite particles, which were prepared by mixing the Ni powder with TiO₂ particles using dry mixing method, on a FTO-glass substrate using a spin coating process. The working electrode was then immersed in the solution of N-719 (Ruthenium) dye at a temperature of 70 °C for 6 h. Moreover, a thin film of platinum (Pt) was deposited on the FTO-glass substrate of the counter electrode using an E-beam evaporator. 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. This study also examined the effects of the mass ratio of TiO₂ to Ni and the number of coating of TiO₂ particles (or TiO₂/NiO composite particles) colloid on the power conversion efficiency of the DSSC. Most importantly, this study shows that the power conversion efficiency of the DSSC with TiO₂/NiO composite particles (3.80%) substantially exceeds that of the conventional DSSC (3.27%) due to the effects of the NiO barrier and the n–p junction.     

The effect of SWCNT with the functional group deposited on the counter electrode on the dye-sensitized solar cell

This study investigated the applicability of single wall carbon nanotubes (SWCNT) with the functional group deposited on the FTO-glass (Fluorine doped tin oxide, SnO₂:F) substrate of the counter electrode for a dye-sensitized solar cell (DSSC). A nanocrystalline TiO₂ layer was fabricated on the FTO-glass substrate of the working electrode, and then sintered in a high-temperature furnace. The working electrode with a TiO₂ thin film was immersed in the solution of N-719 (Ruthenium) dye for 12 h. Moreover, the counter electrode with a layer of Ag (or without a layer of Ag) and a layer of SWCNT, which were (or was) fabricated in that order on the FTO-glass substrate, was subsequently prepared. Finally, the DSSC was assembled, the power conversion efficiency of the DSSC was measured using an I–V measurement system, and the incident photo conversion efficiency (IPCE) of the DSSC was obtained using the phase-locked loop optical chopper. This study also examined the effects of a layer of Ag deposited on the FTO-glass substrate, the type of organic solvent (such as DMAC and acetylacetone), and the sintering temperature on the performance of the DSSC. This film of SWCNT/Ag markedly increased the IPCE from 3.9% (conventional DSSC with a thin film of platinum on the FTO-glass substrate of the counter electrode) to 15.3% (DSSC with SWCNT/Ag/acetylacetone), as the wavelength of the light was 380 nm. Furthermore, as the wavelength of the light is 550 nm, the IPCE of the DSSC with SWCNT/Ag/acetylacetone (6.8%) becomes nearly equal to that of conventional DSSC (7.2%). Most interestingly, this study shows that the power conversion efficiency of the DSSC with SWCNT/Ag/acetylacetone (1.3037%) is not inferior to that of DSSC with a thin film of platinum on the counter electrode (1.25%).     

The effects of the thickness of TiO2 films on the performance of dye-sensitized solar cells

Nanocrystalline anatase TiO₂ thin films with different thicknesses (0.5-2.0 μm) have been deposited on ITO-coated glass substrates by a sol-gel method and rapid thermal annealing for application as the work electrode for dye-sensitized solar cells (DSSC). From the results, the increases in thickness of TiO₂ films can increase adsorption of the N3 dye through TiO₂ layers to improve the short-circuit photocurrent (J_sc) and open-circuit voltage (V_oc), respectively. However, the J_sc and V_oc of DSSC with a TiO₂ film thickness of 2.0 μm (8.5 mA/cm² and 0.61 V) are smaller than those of DSSC with a TiO₂ film thickness of 1.5 μm (9.2 mA/cm² and 0.62 V). It could be due to the fact that the increased thickness of TiO₂ thin films also resulted in a decrease in the transmittance of TiO₂ thin films thus reducing the incident light intensity on the N3 dye. An optimum power conversion efficiency (η) of 2.9% was obtained in a DSSC with the TiO₂ film thickness of 1.5 μm.     

Dye-sensitized TiO2 film with bifunctionalized zones for photocatalytic degradation of 4-cholophenol

A new strategy to photocatalytic degradation of 4-cholophenol (4-CP) under visible light irradiation was described. The TiO₂ film deposited on an ordinary glass sheet was distributed into two zones. One zone was sensitized by N719 dye and fabricated to be a sandwich type cell with a similar structure of dye-sensitized solar cells. The other zone was inserted into pollutants solution for degradation. A highly oxidized overvoltage anode was achieved from the dye-sensitized zone. The bifunctionalized TiO₂ film and the anode could degrade 4-chlorophenol in two separate reactors with 97% and 96% removal of 4-CP after 5 h, respectively. The degradation efficiency could be improved by addition of FeSO₄. The as-prepared bifunctionalized TiO₂ film was comparably stable in the process of degradation.     

The optical properties of nanoporous structured titanium dioxide and the photovoltaic efficiency on DSSC

This study examined the characterization of nanoporous structured titanium dioxide and its application to dye-sensitized solar cells (DSSCs). TEM revealed nanopore sizes of 10.0 nm with a regular hexagonal form. When nanoporous structured TiO₂ was applied to DSSC, the energy conversion efficiency was enhanced considerably compared with that using nanometer sized TiO₂ prepared using a hydrothermal method. The energy conversion efficiency of the DSSC prepared from nanoporous structured TiO₂ was approximately 8.71% with the N719 dye under 100 mW cm⁻² simulated light. FT-IR spectroscopy showed that the dye molecules were attached perfectly to the surface and more dye molecules were absorbed on the nanoporous structured TiO₂ than on the nano-sized TiO₂ particles prepared using a conventional hydrothermal method. Electrostatic force microscopy (EFM) showed that the electrons were transferred rapidly to the surface of the nanoporous structured TiO₂ film.     

The effects of electronic structure of non-metallic doped TiO<Subscript>2</Subscript> anode and co-sensitization on the performance of dye-sensitized solar cells

N/TiO₂, S/TiO₂, and N S/TiO₂ nanocrystalline films anode were obtained by doping non-metallic element N and S which could change the LUMO of anode, leading to the easy injection of electron from the excited state of dye molecule to the conduction band of semiconductor, and thus improving the photoelectric conversion efficiency and reducing the impedance of solar cells. The anode films treated by titanium tetrachloride and co-sensitized by P3HT/N719 were also studied. The absorption region of P3HT/N719 covered the entire visible region in the solar cells. The solar cell based on N/TiO₂ anode film treated by titanium tetrachloride and P3HT/N719 showed a short-circuit current density of 10.20 mA/cm², open-circuit voltage of 0.557 V, and photoelectric conversion efficiency of 2.55%.     

Effect of atomic layer deposited ultra thin HfO2 and Al2O3 interfacial layers on the performance of dye sensitized solar cells

The objective of this work was to investigate the improvement in performance of dye sensitized solar cells (DSSCs) by depositing ultra thin metal oxides (hafnium oxide (HfO₂) and aluminum oxide (Al₂O₃)) on mesoporous TiO₂ photoelectrode using atomic layer deposition (ALD) method. Different thicknesses of HfO₂ and Al₂O₃ layers (5, 10 and 20 ALD cycles) were deposited on the mesoporous TiO₂ surface prior to dye loading process used for fabrication of DSSCs. It was observed that the ALD deposition of ultrathin oxides significantly improved the performance of DSSCs and that the improvement in the DSSC performance depends on the thickness of the deposited HfO₂ and Al₂O₃ films. Compared to a reference DSSC the incorporation of a HfO₂ layer resulted in 69% improvement (from 4.2 to 7.1%) in the efficiency of the cell and incorporation of Al₂O₃ (20 cycles) resulted in 19% improvement (from 4.2 to 5.0%) in the efficiency of the cell. These results suggest that ultrathin metal oxide layers affect the density and the distribution of interface states at the TiO₂/organic dye and TiO₂/liquid electrolyte interfaces and hence can be utilized to treat these interfaces in DSSCs.     

A three-dimensional electrode for photoelectrochemical cell: TiO2 coated ITO mesoporous film

In this letter, TiO₂ coated ITO mesoporous film was prepared by dipping doctor-blade ITO mesoporous film in TiO₂ sol, followed by sintering at 500 °C for 30 min. The CdS quantum dots (QDs) were deposited on TiO₂ coated ITO mesoporous film using sequential chemical bath deposition (S-CBD) method to form a three-dimensional (3D) electrode. The photo-activity of ITO mesoporous film/TiO₂/CdS electrode was investigated by forming a photoelectrochemical cell, which indicated that the ITO mesoporous film/TiO₂/CdS electrode was efficient in photoelectrochemical cell as a working electrode. The 3D electrode showed lower performance than the conventional electrode of TiO₂ mesoporous film/CdS, and more works are needed to improve the performance of 3D electrode.     

Reduced graphene oxide-multiwalled carbon nanotubes hybrid film with low Pt loading as counter electrode for improved photovoltaic performance of dye-sensitised solar cells

In this work, the role of reduced graphene oxide (rGO) with hyperbranched surfactant and its hybridisation with multiwalled carbon nanotubes (MWCNTs) and platinum (Pt) nanoparticles (NPs) as counter electrode (CE) were investigated to determine the photovoltaic performance of dye-sensitised solar cells (DSSCs). Sodium 1,4-bis(neopentyloxy)-3-(neopentyloxycarbonyl)-1,4-dioxobutane-2-sulphonate (TC14) surfactant was utilised as dispersing and stabilising agent in electrochemical exfoliation to synthesise graphene oxide (GO) as initial solution for rGO production prior to its further hybridisation and fabrication as thin film. A chemical reduction process utilising hydrazine hydrate was conducted to produce rGO due to the low temperature process and water-based GO solution. Subsequently, hybrid solution was prepared by mixing 1 wt% MWCNTs into the produced rGO solution. TC14-rGO and TC14-rGO_MWCNTs hybrid solution were transferred into fluorine-doped tin oxide substrate to fabricate thin film by spraying deposition method. Finally, the CE films were prepared by coating with thin Pt NPs. Photoanode film was prepared by a two-step process: hydrothermal growth method to synthesise titanium dioxide nanowires (TiO₂ NWs) and subsequent squeegee method to apply TiO₂ NPs. According to solar simulator measurement, the highest energy conversion efficiency (η) was achieved by using CE-based TC14-rGO_MWCNTs/Pt (1.553%), with the highest short current density of 4.424 mA/cm². The highest η was due to the high conductivity of CE hybrid film and the morphology of fabricated TiO₂ NWs/TiO₂ NPs. Consequently, the dye adsorption was high, and the photovoltaic performance of DSSCs was increased. This result also showed that rGO and rGO_MWCNTs hybrid can be used as considerable potential candidate materials to replace Pt gradually.     

Analyzing the efficiency of nanostructured Sm3+- and Gd3+-doped TiO2 and constructing DSSCs using efficacious photoanodes

The rare earth elements, gadolinium and samarium, are doped with TiO₂ by hydrothermal synthesis technique to study the photoconversion performance of a photoanode in a dye-sensitized solar cell (DSSC). The obtained materials are subjected to the characterizations XRD, HR-TEM, UV–Vis spectroscopy, and XPS. DSSCs are fabricated using N719 dye, redox electrolyte, and platinum counter electrode. Charge-transfer ability was investigated using electrochemical impedance spectroscopy (EIS) on DSSCs. The efficiencies of DSSCs are influenced by the electron transport within the TiO₂–dye–electrolyte system. After the fabrication and simulation, among the two, Gd³⁺-doped TiO₂ gives the desired outcomes and higher efficiency (5.542%) than the pure and Sm³⁺-doped TiO₂ and thus it proves to be a superior solar cell anode material.

     

Fabrication and properties of meso-macroporous electrodes screen-printed from mesoporous titania nanoparticles for dye-sensitized solar cells

A meso-macroporous TiO₂ film electrode was fabricated by using mesoporous TiO₂ (m-TiO₂) nanoparticles through a screen-printing technique in order to efficiently control the main fabrication step of dye-sensitized solar cells (DSSCs). The qualities of the screen-printed m-TiO₂ films were characterized by means of spectroscopy, electron microscopy, nitrogen adsorption–desorption and photoelectrochemical measurements. Under the optimal paste composition and printing conditions, the DSSC based on the meso-macroporous m-TiO₂ film electrode exhibits an energy conversion efficiency of 4.14%, which is improved by 1.70% in comparison with DSSC made with commercially available nonporous TiO₂ nanoparticles (P25, Degussa) electrode printed with a similar paste composition. The meso-macroporous structure within the m-TiO₂ film is of great benefit to the dye adsorption, light absorption and the electrolyte transportation, and then to the improvement of the overall energy conversion efficiency of DSSC.     

Physico-chemical, photoelectrochemical and photocatalytic properties of electrodeposited nanocrystalline titanium dioxide thin films

Crystal structure and microstructural properties of titanium dioxide (TiO₂) thin films prepared by cathodic electrodeposition on indium-tin-oxide coated glass substrates from aqueous peroxo-titanium complex solutions have been investigated. The electrodeposited TiO₂ thin film electrode exhibited anodic photocurrent upon visible light irradiation, indicating the typical behavior of n-type semiconductor. The photodecomposition of CH₃CHO by such thin films on exposure to ultraviolet light illumination was also observed.     

Structural and dielectric properties of Ba0.7Sr0.3TiO3 thin films grown on thin Bi layer-coated Pt(111)/Ti/SiO2/Si substrates

In this work, the growth and study of dielectric properties of Ba_0.7Sr_0.3TiO₃ (BST) thin films grown on thin Bi layer coated Pt(111)/Ti/SiO₂/Si substrates, depending on thin Bi layer thickness is reported. The BST thin film (thickness 180 nm) grown on 10-nm-thick Bi layer exhibited more improved structural and dielectric properties than that grown on bare Pt(111)/Ti/SiO₂/Si substrate. The 10-nm-thick Bi layer in optimum configuration was effective for the grain growth of BST phase and suppressed the formation of the oxygen-deficient layer at the interface between the BST thin film and bottom electrode, which resulted in an increase in dielectric constant and a decrease in leakage current density of the Pt/BST thin film/Pt capacitor.     

Rapid thermal melted TiO2 nano-particles into ZnO nano-rod and its application for dye sensitized solar cells

TiO₂ nano-particles with an anchored ZnO nano-rod structure were synthesized using the hydrothermal method to grow ZnO nano-rods and coated TiO₂ nano-particles on ZnO nano-rods using the rapid thermal annealing method on ITO conducting glass pre-coated with nano porous TiO₂ film. The XRD study showed that there was little difference in crystal composition for various types of TiO₂ nano-particles anchored to ZnO nano-rods. The as-prepared architecture was characterized using field-emission scanning electron microscopy (FE-SEM). Films with TiO₂ nano-particles anchored to ZnO nano-rods were used as electrode materials to fabricate dye sensitized solar cells (DSSCs). The best solar energy conversion efficiency of 2.397% was obtained by modified electrode material, under AM 1.5 illumination, achieved up to J_sc = 15.382 mA/cm², V_oc = 0.479 V and fill factor = 32.8%.     

Chemically deposited TiO2/CdS bilayer system for photoelectrochemical properties

In the present investigation, TiO₂, CdS and TiO₂/CdS bilayer system have been deposited on the fluorine doped tin oxide (FTO) coated glass substrate by chemical methods. Nanograined TiO₂ was deposited on FTO coated glass substrates by successive ionic layers adsorption and reaction (SILAR) method. Chemical bath deposition (CBD) method was employed to deposit CdS thin film on pre-deposited TiO₂ film. A further study has been made for structural, surface morphological, optical and photoelectrochemical (PEC) properties of FTO/TiO₂, FTO/CdS and FTO/TiO₂/CdS bilayers system. PEC behaviour of FTO/TiO₂/CdS bilayers was studied and compared with FTO/CdS single system. FTO/TiO₂/CdS bilayers system showed improved performance of PEC properties over individual FTO/CdS thin films.     

TiO2 coated urchin-like SnO2 microspheres for efficient dye-sensitized solar cells

Urchin-like SnO2 microspheres have been grown for use as photoanodes in dye-sensitized solar cells （DSSCs）. We observed that a thin layer coating of TiO2 on urchin-like SnO2 microsphere photoanodes greatly enhanced dye loading capability and light scattering ability, and achieved comparable solar cell per- formance even at half the thickness of a typical nanocrystalline TiO2 photoanode. In addition, this photoanode only required attaching -55% of the amount of dye for efficient light harvesting compared to one based on nanocrystalline TiO2. Longer decay of transient photovoltage and higher charge recombination resistance evidenced from electrochemical impedance spectroscopy of the devices based on TiO2 coated urchin-like SnO2 revealed slower recombination rates of electrons as a result of the thin blocking layer of TiO2 coated on urchin- like SnO2. TiO2 coated urchin-like SnO2 showed the highest value （76.1 ms） of electron lifetime （＇r） compared to 2.4 ms for bare urchin-like SnO2 and 14.9 ms for nanocrystalline TiO2. TiO2 coated SnO2 showed greatly enhanced open circuit voltage （Voc）, short-circuit current density （Jsc） and fill factor （FF） leading to a four-fold increase in efficiency increase compared to bare SnO2. Although TiO2 coated urchin-like SnO2 showed slightly lower cell efficiency than nanocrystalline TiO2, it only used a half thickness of photoanode and saved -45% of the amount of dye for efficient light harvesting compared to normal nanocrystalline TiO2.     

TiO2 thin films for dyes photodegradation

The aim of the present study is to investigate the influence of the TiO₂ specific surface (powder, film) on the photocatalytic degradation of methyl orange. Porous TiO₂ films were deposited on transparent conducting oxide substrates by spray pyrolysis deposition. The films were characterized by X-ray diffraction (XRD), Scanning Electronic Microscopy, and the UV-Vis spectroscopy. The XRD spectra of nanoporous TiO₂ films revealed an anatase, crystalline structure that is known as the most suitable structure in photocatalysis. The average thickness of the films was 260 nm and the measured band gap is 3.44 eV. The influence of the operational parameters (dye concentration, contact time) on the degradation rate of the dye on TiO₂ was examined. There were calculated the kinetic parameters and the process efficiency. Using thin films of TiO₂ is technologically recommended but raises problems due to lowering the amount of catalyst available for the dye degradation.     

Growth of highly oriented iridium oxide bottom electrode for Pb(Zr,Ti)O<Subscript>3</Subscript> thin films using titanium oxide seed layer

Due to its low resistivity and excellent thermal stability, IrO₂ has attracted attention as an alternative for electrode material in ferroelectric integrated circuit applications. Oriented growth of IrO₂ electrode film was investigated with the goal to control the texture of the PZT thin film. IrO₂ films were prepared by DC reactive sputtering. PZT film was prepared by RF magnetron sputtering single target deposition method. The whole layer stack was grown onto amorphous thermal oxide of a silicon wafer. The results indicate that IrO₂ thin film was preferentially (200) oriented when a TiO₂ seeding layer was used. The orientation relationships along the whole PZT(111)/IrO₂(200)/TiO₂(200)/Ti structure was discussed.     

Enhanced efficiency of tri-layered dye solar cells with hydrothermally synthesized titania nanotubes as light scattering outer layer

In the present study dye sensitized solar cells (DSSCs) have been fabricated with a tri-layer photo anode consisting of hydrothermally prepared titania nano tubes (TNT) having a diameter of 9-10 nm and length of several micrometers as outer layer, P25 TiO₂ powder as transparent light absorbing middle layer and a compact TiO₂ inner layer to improve the adhesion of different layers on a transparent conducting oxide coated substrate. In comparison to cells fabricated using TNTs or P25 alone, the tri-layer DSSCs exhibit an enhanced efficiency of 7.15% with a current density of 17.12 mA cm^− 2 under AM 1.5 illumination. The enhancement is attributed to the light scattering generated by TNTs aggregates, reduction in electron transport resistance at the TiO₂/dye/electrolyte interface and an improvement in electron life-time.