Optimisation of the electrochromic properties of Nb2O5 thin films produced by sol–gel route using factorial design

Electrochemical and electrochromical properties of oxide films are dependent on their microstructure and morphological properties. Thus, the effects of three preparation variables on the electrochemical and electrochromical properties of Nb₂O₅ thin films prepared by the Pechini method were investigated. In order to minimise the number of experiments, a factorial design 2³ was used. The effects of the following variables: CA/EG molar ratio, CA/[Nb] molar ratio and calcination temperature were evaluated. Films prepared with the resin composition CA/EG=1 : 4, CA/[Nb]=10 : 1 and calcined at 500°C, showed the highest values of intercalation charge, transmittance variation and coloration efficiency, 22 mC/cm², 84% and 23 cm² C⁻¹, respectively.     

Experimental investigation and analysis of a new photoelectrochemical reactor for hydrogen production

In this research paper, an experimental investigation of photoactive material titanium dioxide (TiO₂) coated on 180 cm² 316 stainless steel anode is undertaken to study the photoresponse on photoelectrochemical (PEC) hydrogen production. The TiO₂ nanoparticles are first prepared via sol-gel method. A large surface 316 stainless steel anode is coated with TiO₂ nanoparticles by a dip coating apparatus at a withdraw rate of 2.5 mm/s. The nanoparticles are carried on the stainless steel substrate by two-step annealing procedure. The potentiostatic studies confirm the photoactivity of TiO₂ nanoparticles in a photoelectrochemical reactor when exposed to solar ultraviolet (UV) light. The photon to current efficiency measurements carried out on the PEC reactor with TiO₂ coated large surface stainless steel as photoanode demonstrate a significant increase of photoresponse in UV light compared to the uncoated stainless steel prepared under similar conditions. Upon illumination at a power density of 600 W/m², the hydrogen production is observed in TiO₂ coated stainless steel substrate at a measured rate of 51 ml/h while no illumination conditions show a production rate of 42 ml/h. In comparative assessments, the TiO₂ coated substrate shows an increase in photocurrent of 10 mA with an energy efficiency of 1.32% and exergy efficiency of 3.42% at an applied potential of 1.6 V. The present results show a great potential for titanium nanoparticles semiconductor metal oxide in photoelectrochemical hydrogen production application.     

Mix-solvent-thermal method for the synthesis of anatase nanocrystalline titanium dioxide used in dye-sensitized solar cell

Nanocrystalline TiO₂ with almost pure anatase form has been synthesized through the Mix-solvent-thermal method (MST) by using TiCl₄ as the starting material. The mean size of the synthesized TiO₂ is 10 nm with narrow distribution. High-performance dye-sensitized solar cell with nanocrystalline TiO₂ electrode formed from MST was achieved. Its I_sc and V_oc values reached 21.62 mA/cm² and 727.9 mV, respectively, and the photovoltaic conversion efficiency reached 9.13%, i.e. 7.5% higher than those of solar cells with TiO₂ made from the traditional precursor of titanium alkoxides. To our knowledge they are the highest values obtained from the solar cells with nanocrystalline TiO₂ electrode formed from the hydrolysis of TiCl₄.     

Iron oxide (n-Fe2O3) nanowire films and carbon modified (CM)-n-Fe2O3 thin films for hydrogen production by photosplitting of water

Iron oxide n-Fe₂O₃ nanowire photoelectrodes were synthesized by thermal oxidation of Fe metal sheet (Alfa Co. 0.25 mm thick) in an electric oven then tested for their photoactivity. The photoresponse of the n-Fe₂O₃ nanowires was evaluated by measuring the rate of water splitting reaction to hydrogen and oxygen, which is proportional to photocurrent density, J_p. The optimized electric oven-made n-Fe₂O₃ nanowire photoelectrodes showed photocurrent densities of 1.46 mA cm⁻² at measured potential of 0.1 V/SCE at illumination intensity of 100 mW cm⁻² from a Solar simulator with a global AM 1.5 filter. For the optimized carbon modified (CM)-n-TiO₂ synthesized by thermal flame oxidation the photocurrent density for water splitting was found to increase by two fold to 3.0 mA cm⁻² measured at the same measured potential and the illumination intensity. The carbon modified (CM)-n-Fe₂O₃ electrode showed a shift of the open circuit potential by −100 mV/SCE compared to undoped n-Fe₂O₃ nanowires. A maximum photoconversion efficiency of 2.3% at applied potential of 0.5 V/E_aoc was found for CM-n-Fe₂O₃ compared to 1.69% for n-Fe₂O₃ nanowires at higher applied potential of 0.7 V/E_aoc. These CM-n- Fe₂O₃ and n- Fe₂O₃ nanowires thin films were characterized using photocurrent density measurements under monochromatic light illumination, UV-Vis spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM).     

Dye-sensitized solar cell based on Rose Bengal dye and nanocrystalline TiO2

Dye-sensitized solar cell is fabricated using Rose Bengal dye (RB) for sensitization of nanocrystalline TiO₂ and that imparts extension in spectral response towards visible region by modifying the semiconductor surface. Further, the photoresponse of the cell was evaluated by analyzing its J–V and impedance characteristics under illumination with metal halide light source of 400 W with an incident light of 73 mW/cm². Various photovoltaic parameters like J_sc, V_oc, FF were evaluated and found to be 3.22 mA, 890 mV, 0.53, respectively, resulting conversion efficiency (η) of 2.09%. Impedance analysis of the cell was carried out to investigate the internal resistance of the cell by recording Cole–Cole plots in between real and imaginary impedance in dark and with illumination under variable biasing, i.e. from 0 to 3 V.     

Photoelectrochemical water splitting on highly smooth and ordered TiO2 nanotube arrays for hydrogen generation

To improve the photoelectrochemical (PEC) water splitting efficiency for hydrogen production, we reported the fabrication of lotus-root-shaped, highly smooth and ordered TiO₂ nanotube arrays (TiO₂ NTs) by a simple and effective two-step anodization method. The TiO₂ NTs prepared in the two-step anodization process (2-step TiO₂ NTs) showed better surface smoothness and tube orderliness than those of TiO₂ NTs prepared in one-step anodization process (1-step TiO₂ NTs). Under illumination of 100 mW/cm² (AM 1.5, simulated solar light) in 1 M KOH solution, water was oxidized on the 2-step TiO₂ NTs electrode with higher efficiency (incident-photon-to-current efficiency of 43.4% at 360 nm and photocurrent density of 0.90 mA/cm² at 1.23 V_RHE) than that on the 1-step TiO₂ NTs electrode. The effective photon-to-hydrogen conversion efficiency was found to be 0.18% and 0.49% for 1-step TiO₂ NTs and 2-step TiO₂ NTs, respectively. These results suggested that the structural smoothness and orderliness of TiO₂ NTs played an important role in improving the PEC water splitting application for hydrogen generation.     

Highly efficient large area (10.5%, 1376 cm) thin-film CdS/CdTe solar cell

Highly efficient large area (10.5%, 1376 cm²) thin-film CdS/CdTe solar cell sub-module has been fabricated. Very recently we also have fabricated a very large area sub-module of aperture area 5413 cm² exhibiting a conversion efficiency of 8.4%. Such a high efficiency has been achieved by depositing all the constituent films such as SnO₂: F, CdS and CdTe having greater uniformity and better quality under atmospheric pressure conditions. A post deposition treatment of CdTe surface with CdCl₂ has been optimized to improve the overall solar cell output performance significantly.     

Environment-friendly energy from all-carbon solar cells based on fullerene-C60

An efficient single layer organic solar cell based on plain buckminsterfulerence (C₆₀) has been fabricated. By inserting a very thin N,N′-bis(naphthalene-1-yl)-N,N′-bis(phenyl)benzidine layer between the indium tin oxide and single C₆₀ active layer, a short-circuit current of 1.98 mA/cm² and an open-circuit voltage of 0.52 V are obtained under 100 mW/cm² AM1.5G simulated illumination. The highest power conversion efficiency of 0.414% based on plain C₆₀ is thus demonstrated, which is the first step to realize an environment-friendly energy source.     

Large-area high efficiency single crystalline silicon solar cells

This paper reports on a 100 cm² single crystalline silicon solar cell with a conversion efficiency of 19.44% (J_sc = 37.65 mA/cm², V_oc = 638 mV, FF = 0.809). The cell structure is as simple as only applying the textured surface, oxide passivation, and back surface field by the screen printing method. The comparison between cell performances of the CZ (Czochralski) and FZ (Floating zone) silicon substrates was investigated. The higher efficiency cells were obtained for the FZ substrate rather than the CZ substrate. The influence of the phosphorus concentration of the emitter on the cell efficiency has also been investigated. A good result was obtained when the surface concentration of phosphorus was 3 × 10²⁰ cm⁻³ and the junction depth was about 0.6 μm.     

Ni/YSZ and Ni–CeO2/YSZ anodes prepared by impregnation for solid oxide fuel cells

In this paper, Ni/YSZ and Ni–CeO₂/YSZ anodes for a solid oxide fuel cell (SOFC) were prepared by tape casting and vacuum impregnation. By this method, the Ni content in the anode could be reduced compared to the traditional tape casting method. It was found that adding CeO₂ into the Ni/YSZ anode by a Ni(NO₃)₂ and Ce(NO₃)₃ mixed impregnation could further enhance cell performance. This was investigated in H₂ at 1073 K. XRD patterns indicated that CeO₂ and Ni were separate phases, and the CeO₂ addition could enhance the Ni dispersion on the YSZ framework surface which was observed by SEM images. It was shown that adding CeO₂ into the Ni anodes could decrease the cell polarization resistance. The maximum power density for cells with 25 wt.% Ni, 5 wt.% CeO₂–25 wt.% Ni/YSZ, or 10 wt.% CeO₂–25 wt.% Ni/YSZ anode was 230 mW cm⁻², 420 mW cm⁻² and 530 mW cm⁻², respectively, in H₂ at 1073 K. The OCV for these cells was 1.05–1.09 V, indicating that a dense electrolyte film was obtained by co-firing porous YSZ layer and dense YSZ layer.     

Electrochemical deposition of Zn3P2 thin film semiconductors on tin oxide substrates

Zn₃P₂ semiconductor thin films were prepared by electrodeposition technique form aqueous solutions. The deposition mechanism was investigated by cyclic voltammetry technique. Crystal structure, morphology and composition of as deposited and annealed Zn₃P₂ thin films grown on SnO₂/glass substrates were determined by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray analysis. X-ray diffraction data indicated the formation of Zn₃P₂ as the predominant phase for both as-deposited and annealed films. The compositions of the deposited films were controlled by the bath temperature, deposition potential and Zn/P ratio in the solution.The dark current–voltage measurements of SnO₂/Zn₃P₂/C devices indicated a rectifying behavior and a reverse saturation current density of 1.7×10⁻⁷ A/cm², which is in good accordance with that obtained from films prepared using vacuum technique. Also, the capacitance–voltage measurements showed that the number of interface states and the built in potential are in the order of 5×10⁻⁹ cm⁻³ and 0.85 V, respectively. These preliminary results for Zn₃P₂ thin films reveal that, this semiconductor material can be used for solar cell applications.     

The study of Au/MoS2 anode catalyst for solid oxide fuel cell (SOFC) using H2S-containing syngas fuel

Au/MoS₂ is a promising anode catalyst for conversion of all components of H₂S-containing syngas in solid oxide fuel cell (SOFC). MoS₂-supported nano-Au particles have catalytic activity for conversion of CO when syngas is used as fuel in SOFC systems, thus preventing poisoning of MoS₂ active sites by CO. In contrast to use of MoS₂ as anode catalyst, performance of Au/MoS₂ anode catalyst improves when CO is present in the feed. Current density over 600 mA cm⁻² and maximum power density over 70 mW cm⁻² were obtained at 900 °C, showing that Au/MoS₂ could be potentially used as sulfur-tolerant catalyst in fuel cell applications.     

Synthesis and properties of La0.6Sr0.4CoO3−δ nanopowder

Uniform nanopowders of La_0.6Sr_0.4CoO_3−δ (LSC) were synthesized by the combined citrate–EDTA method. The precursor solution was prepared from nitrates of the constituent metal ion, citric acid and EDTA with a pH value controlled by ammonia. The obtained product was characterized by TG/DTA, XRD, SEM, and BET measurements. The single perovskite phase could form completely after sintering at the temperature of 900 °C. There was no significant effect of the precursor solution pH value on the perovskite phase formation temperature; however, LSC powders prepared from the precursors with different pH values showed specific shapes. The morphology of La_0.6Sr_0.4CoO_3−δ powder was also optimized with proper surfactant addition. The sintered La_0.6Sr_0.4CoO_3−δ bulk samples exhibited an electrical conductivity of 1867 S cm⁻¹ in air at 800 °C. The impedance spectra of a symmetric LSC cathode on a GDC electrolyte substrate were measured and polarization resistance (R_p) values of 0.17 Ω cm² at 700 °C and 0.07 Ω cm² at 750 °C in air were obtained.     

Preparation and characterization of sulfonated polysulfone/titanium dioxide composite membranes for proton exchange membrane fuel cells

In the present study, sulfonated polysulfone (sPS)/titanium dioxide (TiO₂) composite membranes for use in proton exchange membrane fuel cells (PEMFCs) were investigated. Polysulfone (PS) was sulfonated with trimethylsilyl chlorosulfonate in 1,2 dichloroethane at ambient temperatures. It was shown that the degree of sulfonation is increased with the molar ratio of the sulfonating agent to PS repeat unit. The degree of sulfonation was determined by elemental analysis and ¹H NMR was performed to verify the sulfonation reaction on the PS. Sulfonation levels from 15 to 40% were easily achieved by varying the content of the sulfonating agent. Composite membranes were prepared by blending TiO₂ with sPS solution in DMAC (5 wt.%) by the solution casting procedure. The membranes have been characterized by thermal analysis, water uptake, proton conductivity measurements and single cell performance. The addition of TiO₂ increased the thermal stability but high filler concentrations decreased the miscibility of the composite component, and resulted in brittle membranes. The conductivity values in the range of 10⁻³–10⁻² S/cm were obtained for composite membranes. The conductivities of the membranes show similar increasing trend as a function of operating temperature. The membranes were tested in a single cell operating at 60–85 °C in humidified H₂/O₂. Single fuel cell tests performed at different operating temperatures indicated that sPS/TiO₂ composite membrane is more hydrodynamically stable and also performed better than sPS membranes. The highest performance of 300 mA/cm² was obtained for sPS/TiO₂ membrane at 0.6 V for an H₂–O₂/PEMFC working at 1 atm and 85 °C. The results show that sPS/TiO₂ is a promising membrane material for possible use in proton exchange membrane fuel cells.     

A dye sensitized TiO2 photovoltaic cell constructed with an elastomeric electrolyte

A photovoltaic solar cell employing an elastomeric electrolyte and using a dye-sensitized nanoporous TiO₂ electrode has been assembled. The polymeric electrolyte is poly(epichlorohydrin-co-ethylene oxide) filled with NaI/I₂. This cell exhibits an open-circuit voltage of 0.71 V and a short-circuit current of 0.46 mA cm⁻² under 120 mW cm⁻² of white-light illumination. The overall conversion efficiency of the cell is 0.22%. The polymeric electrolyte behavior under different conditions of external resistance and intensity of light as well as the performance of this photoelectrochemical cell are discussed.     

TiO2 nanotubes for hydrogen generation by photocatalytic water splitting in a two-compartment photoelectrochemical cell

Highly ordered TiO₂ nanotube arrays for hydrogen production have been synthesized by electrochemical anodization of titanium sheets. Under solar light irradiation, hydrogen generation by photocatalytic water splitting was carried out in the two-compartment photoelectrochemical cell without any external applied voltage. The hydrogen gas and oxygen generated on Pt side and on TiO₂ nanotubes side respectively were efficiently separated. The effect of anodization time on the morphology structures, photoelectrochemical properties and hydrogen production was systematically investigated. Due to more charge carrier generation and faster charge transfer, a maximum photoconversion efficiency of 4.13% and highest hydrogen production rate of 97 μmol h⁻¹cm⁻² (2.32 mL h⁻¹cm⁻²) were obtained from TiO₂ nanotubes anodized for 60 min.     

Highly durable inverted-type organic solar cell using amorphous titanium oxide as electron collection electrode inserted between ITO and organic layer

An indium tin oxide/titanium oxide/[6,6]-phenyl C₆₁ butyric acid methyl ester:regioregular poly(3-hexylthiophene)/poly(3,4-ethylenedioxylenethiophene):poly(4-styrene sulfonic acid)/Au type organic solar cell (ITO/TiO_x/PCBM:P3HT/PEDOT:PSS/Au) with 1 cm² active area, which is called “inverted-type solar cell”, was developed using an ITO/amorphous titanium oxide (TiO_x) electrode prepared by a sol-gel technique instead of a low functional electrode such as Al. The power conversion efficiency (η) of 2.47% was obtained by irradiating AM 1.5G-100 mW cm⁻² simulated sunlight. We found that a photoconduction of TiO_x by irradiating UV light containing slightly in the simulated sunlight was required to drive this solar cell. The device durability in an ambient atmosphere was maintained for more than 20 h under continuous light irradiation. Further, when the air-stable device was covered by a glass plate with a water getter sheet which was coated by an epoxy-UV resin as sealing material, the durability was still higher and over 96% of relative efficiency was observed even after continuous light irradiation for 120 h.     

Investigation of IrO2 electrocatalysts prepared by a sulfite-couplex route for the O2 evolution reaction in solid polymer electrolyte water electrolyzers

IrO₂ electrocatalysts were prepared and electrochemically characterized for the oxygen evolution reaction in a Solid Polymer Electrolyte (SPE) electrolyzer. By using a sulfite complex-based preparation procedure, an amorphous iridium oxide precursor was obtained at 80 °C, which was, successively, calcined at different temperatures: 350 °C, 400 °C and 450 °C. A physico-chemical characterization was carried out by X Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and X-ray-photoelectron spectroscopy (XPS). The various IrO₂ catalysts were sprayed onto a Nafion 115 membrane with a loading of 2.5 mg cm⁻² to form the anode. A Pt/C catalyst (Pt loading 0.5 mg cm⁻²) was used as cathode. The best electrochemical performance was obtained for the cell based on the IrO₂ calcined at 350 °C. The maximum current density at high potentials (1.8  V) was about 1.75 A cm⁻². Accelerated time-tests at 2 A cm⁻² demonstrated a suitable stability of the IrO₂ calcined at 350 °C; however, the intrinsic stability appeared to increase with the calcination temperature. The sample calcined at 400 °C could represent a good compromise between performance and intrinsic stability.     

A study of vapor CdCl2 treatment by CSS in CdS/CdTe solar cells

We report the effect of CdCl₂ vapor treatment on the photovoltaic parameters of CdS/CdTe solar cells. Vapor treatment allows combining CdCl₂ exposure time and annealing in one step. In this alternative treatment, the CdS/CdTe substrates were treated with CdCl₂ vapor in a close spaced sublimation (CSS) configuration. The substrate temperature and CdCl₂ powder source temperature were 400 °C. The treatment was done by varying the treatment time (t) from 15 to 90 min. Such solar cells are examined by measuring their current density versus voltage (J-V) characteristics. The open-circuit voltage (V_oc), short circuit current density (J_sc) and fill factor (FF) of our best cell, fabricated and normalized to the area of 1 cm², were V_oc = 663 mV, J_sc = 18.5 mA/cm² and FF = 40%, respectively, corresponding to a total area conversion efficiency of η = 5%. In cells of minor area (0.1 cm²) efficiencies of 8% have been obtained.     

Investigation of pulsed non-melt laser annealing on the film properties and performance of Cu(In,Ga)Se2 solar cells

Pulsed non-melt laser annealing (NLA) has been used for the first time to modify near-surface defects and related junction properties in Cu(In,Ga)Se₂ (CIGS) solar cells. CIGS films deposited on Mo/glass substrates were annealed using a 25 ns pulsed 248 nm laser beam at selected laser energy density in the range 20–60 mJ/cm² and pulse number in the range 5–20 pulses. XRD peak narrowing and SEM surface feature size increase suggest near-surface structure changes. Dual-beam optical modulation (DBOM) and Hall-effect measurements indicate NLA treatment increases the effective carrier lifetime and mobility along with the sheet resistance. In addition, several annealed CdS/CIGS films processed by NLA were fabricated into solar cells and characterized by photo- and dark-J–V and quantum efficiency (QE) measurements. The results show significant improvement in the overall cell performance when compared to unannealed cells. The results suggest that an optimal NLA energy density and pulse number for a 25 ns pulse width are approximately 30 mJ/cm² and 5 pulses, respectively. The NLA results reveal that overall cell efficiency of a cell processed from an unannealed film increased from 7.69% to 13.41% and 12.22% after annealing 2 different samples at the best condition prior to device processing.