F-doped SnO2 Research Articles

Deposition of TiO2 Passivation Layer by Plasma Enhanced Chemical Vapor Deposition between the Transparent Conducting Oxide and Mesoporous TiO2 Electrode in Dye Sensitized Solar Cells

The characteristic of TiO2 passivation layers grown by plasma enhanced chemical vapor deposition as a function of its thickness on F-doped SnO2 (FTO) electrode was investigated. The thickness of TiO2 passivation layer was varied from 30 to 200 nm by controlling the deposition time. The electric resistance of the TiO2 layers was depended on the thickness, so the optimized thickness in enhancing the connection and reducing the recombination of electrons on the surface of FTO electrode was determined. The dye sensitized solar cells fabricated with 40 nm thick TiO2 passivation layer showed the maximum power conversion efficiency of 6.93%. It was due to the effective connection of mesoporous TiO2 and FTO and the prevention of electron recombination from the FTO to electrolyte. The reduced resistance, enlarged electron diffusion length measured by the electrochemical impedance spectroscopy, intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy identified the connection and anti-recombination effect.

Improving Mobility of F-Doped SnO2Thin Films by Introducing Temperature Gradient during Low-Pressure Chemical Vapor Deposition

High mobility is required to suppress free-carrier absorption in the near-infrared (NIR) region. Toward this end, we investigated the properties of a F-doped SnO2 (FTO) film deposited using low-pressure chemical vapor deposition (LPCVD) and found that the optimum deposition temperature varied with film thickness. On the basis of this result, we introduced a temperature gradient into LPCVD, which resulted in an improvement in the mobility of F-doped SnO2 on glass to 77.5 cm2 V-1 s-1.

Improving Mobility of F-Doped SnO2 Thin Films by Introducing Temperature Gradient during Low-Pressure Chemical Vapor Deposition

High mobility is required to suppress free-carrier absorption in the near-infrared (NIR) region. Toward this end, we investigated the properties of a F-doped SnO2 (FTO) film deposited using low-pressure chemical vapor deposition (LPCVD) and found that the optimum deposition temperature varied with film thickness. On the basis of this result, we introduced a temperature gradient into LPCVD, which resulted in an improvement in the mobility of F-doped SnO2 on glass to 77.5 cm2 V-1 s-1.

Dense TiO2 films grown by sol–gel dip coating on glass, F-doped SnO2, and silicon substrates

Abstract

Electrical Properties of Fluorine Doped Tin Dioxide Film Grown by Spray Method

Low resistivity, fluorine-doped tin dioxide thin films were deposited on glass substrates by spray pyrolysis. These films were prepared with different F-doping concentrations from 0 to 33 mol%. The structure of these films was investigated by X-ray diffraction and the surface morphology by Scanning Electron Microscopy. Sample compositions were evaluated using X-ray Photoemission Spectroscopy. According to these results, the films were all polycrystalline with tetragonal crystal structures. Hall measurements were used to probe the dependence of the resistivity on temperature for un-doped SnO2 and F-doped SnO2. The resistivity of un-doped SnO2 slightly increased with increasing temperature. Conversely, the resistivity of F-doped SnO2 slightly decreased with increasing temperature.

Plasma Treatment Effect on Dye-Sensitized Solar Cell Efficiency of Hydrothermal-Processed TiO2 Nanorods

Atmospheric plasma (AP) treatment was carried out on TiO2 nanorods (NRs) that were hydrothermally grown on F-doped SnO2 (FTO)/glass. The effects of AP treatment on the surface of the TiO2 NRs were investigated, where the treatment involved the use of the reactive gases H2, N2, and O2. The surface energy of AP-treated TiO2 NRs was about 1.5 times higher than that of untreated TiO2 NRs (364.3 mJ/m2). After AP treatment, the increase of the peak area ratios of the Ti2O3 and TiO2 peaks in the XPS spectra resulted in a decrease in the number of oxygen vacancies in the TiO2 NRs. The efficiency of a dye-sensitized solar cell (DSSC) based on the N2-plasma-treated TiO2 NRs, which was approximately 1.11%, was about 79% higher than that of a DSSC based on the untreated TiO2 NRs.

Facile fabrication of an efficient BiVO 4 thin film electrode for water splitting under visible light irradiation

An efficient BiVO(4) thin film electrode for overall water splitting was prepared by dipping an F-doped SnO(2) (FTO) substrate electrode in an aqueous nitric acid solution of Bi(NO(3))(3) and NH(4)VO(3), and subsequently calcining it. X-ray diffraction of the BiVO(4) thin film revealed that a photocatalytically active phase of scheelite-monoclinic BiVO(4) was obtained. Scanning electron microscopy images showed that the surface of an FTO substrate was uniformly coated with the BiVO(4) film with 300-400nm of the thickness. The BiVO(4) thin film electrode gave an excellent anodic photocurrent with 73% of an IPCE at 420nm at 1.0V vs. Ag/AgCl. Modification with CoO on the BiVO(4) electrode improved the photoelectrochemical property. A photoelectrochemical cell consisting of the BiVO(4) thin film electrode with and without CoO, and a Pt counter electrode was constructed for water splitting under visible light irradiation and simulated sunlight irradiation. Photocurrent due to water splitting to form H(2) and O(2) was confirmed with applying an external bias smaller than 1.23V that is a theoretical voltage for electrolysis of water. Water splitting without applying external bias under visible light irradiation was demonstrated using a SrTiO(3)Rh photocathode and the BiVO(4) photoanode.

Low temperature processed SnO2 films using aqueous precursor solutions

We present a comparison study of the microstructure developments during aqueous solution deposition of SnO2, particularly, through chemical bath deposition (CBD) and liquid phase deposition (LPD) at very low temperatures (40–75°C). The effects of solution chemistry on the microstructural details and electrical properties of SnO2 thin films are presented and discussed. Smooth, nanoparticulate SnO2 films were obtained from supersaturated precursor solutions with lower precursor concentrations while more aggregated SnO2 films were generated from higher precursor concentrations. Loosely-packed and porous structures were obtained from low supersaturation solutions with very low pHs. The deposition rates were also evaluated under various deposition conditions. XRD result shows that annealing process helps improve the degree of crystallinity of the as-deposited films that are composed of 3–10nm nanocrystalline particles. One advantage of LPD of SnO2 films is in-situ fluorine doping during deposition. The resulting electrical resistivity of F-doped SnO2 films was about 18.7Ωcm after the films were annealed at 450°C.

Voltage enhancement in dye-sensitized solar cell using (001)-oriented anatase TiO2 nanosheets

A nanocrystalline TiO2 (anatase) nanosheet exposing mainly the (001) crystal faces was tested as photoanode material in dye-sensitized solar cells. The nanosheets were prepared by hydrothermal growth in HF medium. Good-quality thin films were deposited on F-doped SnO2 support from the TiO2 suspension in ethanolic or aqueous media. The anatase (001) face adsorbs a smaller amount of the used dye sensitizer (C101) per unit area than the (101) face which was tested as a reference. The corresponding solar cell with sensitized (001)-nanosheet photoanode exhibits a larger open-circuit voltage than the reference cell with (101)-terminated anatase nanocrystals. The voltage enhancement is attributed to the negative shift of flatband potential for the (001) face. This conclusion rationalizes earlier works on similar systems, and it indicates that careful control of experimental conditions is needed to extract the effect of band energetic on the current/voltage characteristics of dye-sensitized solar cell.

Effect of reactive gases in an atmospheric-pressure plasma for dye adsorption on ZnO nanorods

In this study, ZnO nanorods (NRs) were grown on F-doped SnO2 (FTO)/glass substrate by using a chemical bath deposition (CBD) method. The NRs were crystallized well. The surfaces of the NRs were modified using an atmospheric-pressure (AP) plasma containing reactive gases such as O2, H2, and N2. In the case of the Ar/O2 and Ar/N2 plasma-treated ZnO NRs, chemical bonding states and the dye adsorption on the surface of the ZnO layer increased because of -O and -OH radicals. We present the efficiencies of ZnO-NR-based dye-sensitized solar cells (DSSCs) treated with AP plasmas containing reactive gases.

Microstructure analysis of spherical silicon solar cells coated with anti-reflection films

Microstructures of spherical silicon solar cells were investigated by transmission electron microscopy and X-ray diffraction. Optical absorption and photoluminescence of the solar cells were also measured by UV-visible and fluorescence spectroscopy. F-doped SnO2 anti-reflection coating layers were investigated by XRD, and the nanostructures and grain sizes were determined. The present work indicated a guideline for spherical silicon solar cells with higher efficiencies.

Self-aligned TiO2 thin films with remarkable hydrogen sensing functionality

Self-aligned titania thin films of either the rutile or the anatase phase were successfully grown on FTO (F-doped SnO2) substrates with hydrothermal methods. The selection of the targeted phase, either rutile or anatase, in the thin films was controlled by adjusting the content and type of acidic anions such as Cl− and SO42−. The growth kinetics depended on the synthesis temperature and the types of alcohol in the solvent. The self-alignment in both the anatase and rutile thin films was attributed to the minimization of surface energies during growth. The hydrogen sensing characteristics of dense films of both rutile and anatase phases were investigated and there was remarkable improvement of sensitivity response over reported data. It was found that rutile films had higher sensitivity while anatase films had faster response.

Effects of RF and pulsed DC sputtered TiO2 compact layer on the performance dye-sensitized solar cells

We investigated the characteristics of TiO2 compact layers grown by RF and pulsed DC magnetron sputtering on F-doped SnO2 (FTO) electrodes from a TiO2 ceramic target. The morphological and microstructural properties of the formed TiO2 layers were characterized by scanning electronic microscopy and X-ray diffraction. The deposition rate of the compact TiO2 layer by pulsed DC sputtering was much higher than that of RF deposition under the same sputter power and deposition pressure. Moreover, it was found that the power conversion efficiency of the dye-sensitized solar cells (DSCs) is strongly dependent on the thickness of both RF and DC sputtered TiO2 layer inserted between FTO electrode and nanoporous TiO2 layer. The thickness of the sputtered TiO2 layer was changed from 0 to 200nm. The electrochemical impedance spectroscopy (EIS) technique was employed to evaluate the recombination resistance and electron lifetime in DSCs with differently thick TiO2 passivating films. The DSC fabricated on 160nm thick TiO2 passivating FTO electrode showed the maximum power conversion efficiency of 7.90% due to highly effective prevention of the electron transfer to electrolyte.

Suppressed Recombination in Quantum Dot-Sensitized Solar Cells with Blocking Layers on FTO Substrates

The compact and thin TiO2 blocking layers (c-TiO2) were formed on F-doped SnO2 (FTO) substrate in quantum dots-sensitized solar cells (QSSCs) by chemical deposition. The c-TiO2 layers induced indirect contact between electrolyte and FTO electrode, which reduced leakage in QSSCs. The QSSCs showed power conversion efficiency (Eff) of 3.85% in the presence of c-TiO2 layers which leads to 21% improved compared to that without c-TiO2 layers (Eff = 3.18%). The presence of the c-TiO2 layers in QSSCs also improved the stability under illumination.

Photovoltaic property dependence of dye-sensitized solar cells on sheet resistance of FTO substrate deposited via spray pyrolysis

F-doped SnO2 (FTO) glass substrate was successfully fabricated via spray-pyrolysis deposition for use as a transparent conducting substrate in dye-sensitized solar cells (DSSCs). To investigate the performance dependence of DSSCs on the sheet resistance of the FTO films, three types of FTO films with sheet resistance values of 2Ω/□, 4Ω/□, and 10Ω/□ were fabricated. Commercial FTO films having a sheet resistance of 15Ω/□ were prepared for comparison. The structural, electrical, and optical properties of FTO films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), the four-point probe method, and UV–vis spectrometry. The photocurrent–voltage data show that DSSCs fabricated with a sheet resistance of 2Ω/□ exhibit the best photoconversion effciency (∼5.5%) among the four samples. The performance improvement of DSSCs is due to improved short-circuit current density (∼13.7mA/cm2) and fill factor (∼62.3%).

Effect of incorporating copper on resistive switching properties of ZnO films

Undoped and copper-doped ZnO (ZnO:Cu) thin films of wurtzite structure with c-axis orientation were grown on F-doped SnO2 (FTO) substrates by pulsed laser deposition. Typical bipolar and reversible resistance switching effects were observed in these films, and the ratio of high and low resistance state (ON/OFF ratio) increases abruptly by introducing Cu. Based on the impedance spectra of ZnO and ZnO:Cu films, the change of resistance at high and low resistance states is found to be accompanied with the variance of depletion width. Furthermore, the depletion width of ZnO films changes little, while that of ZnO:Cu films varies greatly under different resistance states, which is consistent with the result of that ZnO:Cu films show a much larger ON/OFF ratio than ZnO films. Therefore, the resistance switchings are supposed to be due to the change of depletion width of Schottky barrier.

Analysis of the electrical characteristics of the Ag/ZnO Schottky barrier diodes on F-doped SnO2 glass substrates by pulsed laser deposition

High quality semiconductor layer of n-type ZnO thin film was fabricated on F-doped SnO2 glass substrates by pulsed laser deposition. The Schottky junction diodes with configuration of Ag/ZnO/FTO have been fabricated to study the devices electrical properties by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The results show that the devices have good rectifying behaviors with an ideality factor of 1.64 and a Schottky barrier height of 0.85eV based on the I-V characteristics. Also, Cheung's functions and Norde's method were used to evaluate the I-V characteristics and to obtain the series resistance of the Schottky contact. From the C-V characteristics, the capacitance was determined to increase with decrease of frequencies. C-V measurements have resulted in higher barrier heights than those obtained from I-V measurements. The discrepancy between Schottky barrier heights obtained from I-V and C-V measurements was also interpreted.

Development of Electrodeposition System Employing 8 Rotating Disc Electrodes for Highly Reproducible Synthesis of Zinc Oxide Thin Films

We have designed an electrodeposition system employing multiple rotating disc electrodes (RDE) in a single electrochemical bath, with an aim to develop a mean to obtain homogeneous zinc oxide (ZnO) thin films with a high reproducibility, as the reaction is known to be strongly limited by mass transport. Substrates such as F-doped SnO2 (FTO) coated glass having no electric conduction on the back side were furnished into a geometry of RDEs employing conductive and insulating tapes. The shape of the active electrode area was determined through tests. Also, the influence of the position of the RDE in the electrochemical bath was tested. Having confirmed that neighboring RDEs do not interfere each other, eight RDEs were placed like a roulette in a single electrolytic bath. The resulting eight ZnO samples electrodeposited by using the eight RDE system were almost identical with the standard deviation of less than 0.3% for their thickness.

Mechanism of an AZO-coated FTO film in improving the hydrogen plasma durability of transparent conducting oxide thin films for amorphous-silicon based tandem solar cells

An Al-doped ZnO (AZO)/F-doped SnO2 (FTO) film structure in an amorphous silicon solar cell (a-Si:H) was studied under exposure to hydrogen (H) plasma treatment via a simple spray pyrolysis. A radio-frequency magnetron sputtering method was used to deposit the FTO film first and the subsequent AZO overlayer on top of the FTO. The results of this approach suggest that the AZO film acts as a protection layer for the underlying FTO film and thus provides an excellent interface that protects the film from the direct bombardment with H+ ions and radicals. Even under exposure to H-plasma, the optical (UV-Vis) and electrical properties (Hall measurement) of the AZO/FTO double layer film show improvement in plasma stability in comparison with a single FTO film. Without the AZO overlayer, the reduction of SnO2 to metallic Sn and sub-oxidized SnO can occur in the FTO film. However, after a post-annealing treatment at 400 °C, the degradation of the FTO can be reversed by reoxidizing the Sn–O bonds. This interpretation of the H+ ion diffusion and the Sn–O redox process is confirmed via XPS and SIMS analysis. This investigation provides an opportunity to study the H+ ion diffusion mechanism in a metal oxide matrix in the presence of plasma and thermal effects. The study thus provides an alternative to the conventionally used FTO-based Si solar cells.

Electrochemical synthesis of hierarchical Cu 2O stars with enhanced photoelectrochemical properties

Nanopyramid-assembled three-dimensional (3D) hierarchical Cu 2O stars on F-doped SnO 2 coated glass (FTO) substrates have been successfully synthesized using a rapid and facile electrodeposition approach from aqueous solutions near room temperature. Combined X-ray photoelectron spectroscopy (XPS) and X-ray-induced Cu LMM Auger studies reveal only Cu 2O on the surface of the samples. The Cu 2O stars exhibit superior photocurrent performance over Cu 2O nanoparticles in photoelectrochemical cell applications. In addition, the photocurrent of the Cu 2O samples is due to water splitting.