Photoelectrochemical performance of sprayed n-CdIn2Se4 photoanodes

Cadmium indium selenide thin films have been synthesized by spraying mixture of equimolar solution concentrations of cadmium chloride, indium trichloride and selenourea in aqueous media onto preheated FTO coated glass substrates at optimized substrate temperature and solution concentration. The photoelectrochemical cell configuration of n-CdIn₂Se₄/(1 M NaOH + 1 M Na₂S + 1 M S)/C has been used for investigate the current-voltage characteristics under dark and white light illumination, photovoltaic output, spectral response, photovoltaic rise and decay characteristics. It reveals the film of CdIn₂Se₄ exhibits n-type conductivity. The junction quality factor in dark (n_d) and light (n_l), series and shunt resistance (R_s and R_sh), fill factor (FF) and efficiency (η) for the cell have been estimated. Gartner’s model was used to calculate minority carrier diffusion length and donor concentration (n_D). The observed efficiency and FF of PEC solar cell is 1.95% and 0.37% respectively. Mott-Schottky plot shows the flat-band potential (V_fb) of CdIn₂Se₄ films is −0.655 V/SCE.     

Visible-light-driven ZnIn2S4/CdIn2S4 composite photocatalyst with enhanced performance for photocatalytic H2 evolution

ZnIn₂S₄/CdIn₂S₄ composite photocatalysts (x = 0–1) were successfully synthesized via a hydrothermal route. Compositions of ZnIn₂S₄/CdIn₂S₄ composite photocatalysts were optimized according to the photocatalytic H₂ evolution rate. XRD patterns indicate the as-prepared samples are mixtures of hexagonal and cubic structures. FESEM and TEM images show that the as-prepared samples are composed of flower-like microspheres with wide distribution of diameter. There is obviously distinguishing distribution of Zn, Cd elements among the composite architectures. UV–vis absorption spectra of different compositions exhibit that absorption edges of ZnIn₂S₄/CdIn₂S₄ composites slightly move towards longer wavelengths with the increment of CdIn₂S₄ component. A typical time course of photocatalytic H₂ evolution from an aqueous Na₂SO₃ and Na₂S solution over unloaded and PdS-loaded ZnIn₂S₄/CdIn₂S₄ composite photocatalyst is carried out. The initial activity for H₂ evolution over 0.75 wt% PdS-loaded sample is up to 780 μmol h⁻¹. And the activity of unloaded sample also reaches 490 μmol h⁻¹ with consistent stability.     

Surfactant tunable hierarchical nanostructures of CdIn2S4 and their photohydrogen production under solar light

The hierarchical nanostructures of CdIn₂S₄ were selectively prepared through hydrothermal process in the presence of different surfactants. Structural study demonstrated existence of cubic spinel structure and micro structural study shown a pretty marigold flower like morphology without any surfactant. The effect of surfactants on the morphology and microstructure of CdIn₂S₄ has been studied by using Polyvinyl pyrrolidone (PVP) and Cetyltrimethyl ammonium bromide (CTAB) as a surfactants. The CdIn₂S₄ bipyramids with length of 0.7-1 μm have been obtained using PVP. Interestingly, the nanopetals (thin and transparent) of CdIn₂S₄ are self assembled into hollow spheres in the presence of CTAB. Considering the importance of these unique nanostructures, the growth mechanism has also been proposed. The optical properties demonstrated the band gap in the range of 2.12-2.29 eV which is well within the visible region. In this contest, photocatalytic activity for hydrogen production using the above nanostructures under visible light was also demonstrated. The prima-fascia observations shows that the bipyramidal CdIn₂S₄ exhibit excellent photocatalytic activity for hydrogen production (3238 μmolh⁻¹) than other nanostructures. Being a nanostructured semiconductor chalcogenide with a good stability will also have potential applications in solar cells and LED.     

Some physical investigations on AgInS2 sprayed thin films

AgInS₂ thin films have been prepared on glass substrates by the spray pyrolysis process using an aqueous solution which contains silver acetate (AgCH₃CO₂), thiourea (SC(NH₂)₂) and indium chloride (InCl₃) as precursors. The depositions were carried out in the range of the substrate temperature from 260 to 420 °C. The value of the concentration ratio in the spray solution of indium and silver elements x=[Ag⁺]/[In³⁺] was varied from 1 to 1.5 with [In³⁺]=10⁻² M and [S²⁻]/[In³⁺] was taken constant, equal to 4. The structural study shows that AgInS₂ thin film, prepared at 420 °C using optimal concentration ratio x=1.3 crystallizes in the chalcopyrite phase with a strong (1 1 2) X-ray diffraction line. Moreover, microprobe analysis (EPMA) shows that a nearly stoichiometric composition is obtained for these experimental conditions. Indeed, the atomic percentage of elements were. 24.5, 25.0, 49.5 for Ag, In and S, respectively. On the other hand from transmission and reflectance spectra, the obtained band gap energy is 1.83 eV for such film.     

Photocatalytic H2 evolution on a novel CaIn2S4 photocatalyst under visible light irradiation

A novel visible-light-driven photocatalyst CaIn₂S₄ was synthesized using a facile hydrothermal method followed by a post-calcination process. The influence of the calcination temperature and time on the activities of the photocatalyst was investigated. CaIn₂S₄ exhibits optical absorption predominantly in visible region with an optical band gap of 1.76 eV. Considerable activity for hydrogen evolution from pure water was observed without any sacrificial agents or cocatalysts under visible light irradiation. The maximum hydrogen evolution rate achieved was 30.92 μmol g⁻¹ h⁻¹ without obvious deactivation of the photocatalytic activity for four consecutive runs of 32 h.     

Influence of In2S3 film properties on the behavior of CuInS2/In2S3/ZnO type solar cells

Solar cells of CuInS₂/In₂S₃/ZnO type are studied as a function of the In₂S₃ buffer deposition conditions. In₂S₃ is deposited from an aqueous solution containing thioacetamide (TA), as sulfur precursor and In³⁺. In parallel, variable amounts of In₂O₃ are deposited that have an important influence on the buffer layer behavior. Starting from deposition conditions determined in a preliminary study, a set of parameters is chosen to be most determining for the buffer layer behavior, namely the solution temperature, the concentration of thioacetamide [TA], and the buffer thickness. The solar cell results are discussed in relation with these parameters. Higher efficiency is attained with buffer deposited at high temperature (70 °C) and [TA] (0.3 M). These conditions are characterized by short induction time, high deposition rate and low In₂O₃ content in the buffer. On the other hand, the film deposited at lower temperature has higher In₂O₃ content, and gives solar cell efficiency sharply decreasing with buffer thickness. This buffer type may attain higher conversion efficiencies if deposited on full covering very thin film.     

Photoelectrochemical evaluation of undoped and C-doped CdIn2O4 thin film electrodes

Undoped and C-doped cadmium indate (CdIn₂O₄) thin films and powders were synthesized, characterized, and evaluated for photoelectrochemical water splitting. Both undoped and C-doped CdIn₂O₄ samples have cubic lattices, and the presence of carbonate-type species was confirmed in the C-doped sample by XPS. Doping C into CdIn₂O₄ leads to a red shift (but no separate peak) in light absorption and band gap narrowing. The photocurrent densities of CdIn₂O₄ electrodes are at least three-fold greater than either CdO or In₂O₃ electrodes with equivalent film thickness. Carbon doping further improved the photocurrent densities by 33%. The photoelectrochemical performance of C-doped CdIn₂O₄ was optimized with respect to several synthetic parameters, including the C:In molar ratio and glucose concentration in the spray precursor solution, the calcination temperature, and the film thickness. The present work shows that CdIn₂O₄ is a promising photocatalyst and can be suitably doped to improve the electrochemical properties for solar conversion applications.     

Photoelectrochemical properties of spray deposited n-ZnIn2Se4 thin films

Zinc indium selenide (ZnIn₂Se₄) thin films have been prepared by spraying a mixture of an equimolar aqueous solution of zinc sulphate (ZnSO₄), indium trichloride (InCl₃), and selenourea (CH₄N₂Se), onto preheated fluorine-doped tin oxide (FTO)-coated glass substrates at optimized conditions of substrate temperature and a solution concentration. The photoelectrochemical (PEC) cell configuration of n-ZnIn₂Se₄/1 M (NaOH+Na₂S+S)/C has been used for studying the current voltage (I–V), spectral response, and capacitance voltage (C–V) characteristics of the films. The PEC study shows that the ZnIn₂Se₄ thin films exhibited n-type conductivity. The junction quality factor in dark (n_d) and light (n_l), series and shunt resistance (R_s and R_sh), fill factor (FF) and efficiency (η) for the cell have been estimated. The measured (FF) and η of the cell are, respectively, found to be 0.435% and 1.47%.     

Fabrication of n-Cu2O electrodes with higher energy conversion efficiency in a photoelectrochemical cell

We observed an n-type photoresponse in cuprous oxide films, which were prepared by a simple method of immersing copper plates in a HCl solution of 3 pH at 40°C temperature, when they were used in a PEC cell. This photoresponse was much higher than the previously published values for n-Cu₂O electrodes which were prepared by other methods. The photocurrent obtained was in the order of 0.3 mA/cm² when the cell was illuminated with light intensity of 50 mW/cm². (The semiconductor electrode was biased to get a zero dark current.) The power conversion efficiency of the cell was 0.01%. The maximum quantum efficiency obtained was 15%. It is hoped that these values could be improved with a better understanding of the photoelectrochemical properties of the cell.     

Photoelectrochemical behavior of In2S3 formed on sintered In2O3 pellets

Microcrystals of In₂S₃ were formed on sintered In₂O₃ pellets by sulfurizing in H₂S atmosphere. The flat band potential of compound In₂S₃|In₂O₃ electrodes was evaluated as −1.0 V vs Ag|AgCl in 1 M KOH, 1 M Na₂S, 10⁻² M S. Significantly enhanced photocurrent was observed on compound In₂S₃|In₂O₃ electrodes with a lower degree of sulfurization to that of compound In₂S₃|In₂O₃ electrodes with higher degree of sulfurization. Photocurrent generation of compound In₂S₃|In₂O₃ electrodes was explained from the viewpoint of semiconductor sensitization.     

Pyrite (FeS2) thin films prepared by spray method using FeSO4 and (NH4)2Sx

A simple spray method for the preparation of pyrite (FeS₂) thin films has been studied using FeSO₄ and (NH₄)₂S_x as precursors for Fe and S, respectively. Aqueous solutions of these precursors are sprayed alternately onto a substrate heated up to 120°C. Although Fe–S compounds including pyrite are formed on the substrate by the spraying, sulfurization of deposited films is needed to convert other phases such as FeS or marcasite into pyrite. A single-phase pyrite film is obtained after the sulfurization in a H₂S atmosphere at around 500°C for 30 min. All pyrite films prepared show p-type conduction. They have a carrier concentration (p) in the range 10¹⁶–10²⁰ cm⁻³ and a Hall mobility (μ_H) in the range 200–1 cm²/V s. The best electrical properties (p=7×10¹⁶ cm⁻³, μ_H=210 cm²/V s) for a pyrite film prepared here show the excellence of this method. The use of a lower concentration FeSO₄ solution is found to enhance grain growth of pyrite crystals and also to improve electrical properties of pyrite films.     

3D hierarchical ZnIn2S4: The preparation and photocatalytic properties on water splitting

Hexagonal ZnIn₂S₄ photocatalysts with 3D-hierarchical persimmon-like shape have been successfully synthesized via an oleylamine (OA)-assisted solvothermal method. Hydrogen evolution experiments revealed that the obtained hierarchical ZnIn₂S₄ possessed good photocatalytic activity, e.g. hydrogen production rate reached to 220.45 μmol h⁻¹ and the quantum yield was up to 13.16% when 3% Pt was loaded. Further delicate tuning the percentage of exposed facet of the obtained ZnIn₂S₄ crystals, it was found that the increase of {006} facets, terminated by metal ions, would improve their photocatalytic activity, and the relationship between the crystal structure and photocatalytic properties had been studied.     

Preparation and characterization of spray-deposited Cu2ZnSnS4 thin films

Thin films of Cu₂ZnSnS₄ (CZTS), a potential candidate for absorber layer in thin film heterojunction solar cell, have been successfully deposited by spray pyrolysis technique on soda-lime glass substrates. The effect of substrate temperature on the growth of CZTS films is investigated. X-ray diffraction studies reveal that polycrystalline CZTS films with better crystallinity could be obtained for substrate temperatures in the range 643-683 K. The lattice parameters are found to be a=0.542 and c=1.085 nm. The optical band gap of films deposited at various substrate temperatures is found to lie between 1.40 and 1.45 eV. The average optical absorption coefficient is found to be >10⁴ cm⁻¹.     

Preparation of ZnIn2S4/fluoropolymer fiber composites and its photocatalytic H2 evolution from splitting of water using Xe lamp irradiation

This paper focuses on the preparation of ZnIn₂S₄/fluoropolymer fiber composites and their performance for H₂ evolution from splitting of water using Xe lamp irradiation. Hexafluorobutyl acrylate-co-methacrylic acid (poly(HFBA-co-MAA)) is synthesized by a solution polymerization. Next, the fluoropolymer fibers, which have around 100 nm in average diameter, of poly(HFBA-co-MAA) and polyvinylidene fluoride (PVDF) mixtures are obtained by electrospinning. Then, zinc and indium ions are introduced onto the fiber surface by coordinating with carboxyls of MAA. After that, sulfide ions are incorporated to react with zinc and indium ions by a hydrothermal synthesis. Thus, ZnIn₂S₄ particles of around 800 nm in average size, are obtained and well loaded on the fiber surface. The absorption edge of ZnIn₂S₄/fluoropolymer fiber composites is at 510 nm within the visible-light region. Photocatalytic H₂ evolution from water was investigated using Xe lamp. It was found that the average rate of H₂ evolution of ZnIn₂S₄ powders gradually decreased, while the average rate of H₂ evolution of ZnIn₂S₄/fluoropolymer fiber composites increased from the first to the third run. The average rate of H₂ evolution using the ZnIn₂S₄/fluoropolymer fiber composites as the catalyst achieved 9.1 mL/h in the third run.     

Cetyltrimethylammoniumbromide (CTAB)-assisted hydrothermal synthesis of ZnIn2S4 as an efficient visible-light-driven photocatalyst for hydrogen production

A series of ZnIn₂S₄ photocatalysts was synthesized via a cetyltrimethylammoniumbromide (CTAB)-assisted hydrothermal method. These ZnIn₂S₄ products were characterized by X-ray diffraction (XRD), UV–visible absorption spectra (UV–vis) and scanning electron microscopy (FESEM). The effects of hydrothermal time and CTAB on the crystal structures, morphologies and optical properties of ZnIn₂S₄ products were discussed in detail. The photocatalytic activities of the as-prepared samples were evaluated by photocatalytic hydrogen production from water under visible-light irradiation. It was found that the photocatalytic activities of these ZnIn₂S₄ products decreased with the hydrothermal time prolonging while increased with the amount of CTAB increasing. The highest quantum yield at 420 nm of ZnIn₂S₄ photocatalyst, which was prepared through the CTAB (9.6 mmol)-assisted hydrothermal procedure for 1 h, was determined to be 18.4%. The optimum amount of Pt loaded for the ZnIn₂S₄ photocatalyst was about 1.0 wt%, under the present photocatalytic system.     

Photocurrent enhancement of wide bandgap Bi2O3 by Bi2S3 over layers

Sintered Bi₂O₃ pellets exhibited insulating properties at room temperature. Partial reduction of sintered Bi₂O₃ pellets increased the conductivity. Reduced Bi₂O₃ pellets exhibited n-type semiconductor properties. Microcrystals of Bi₂S₃ were formed on sintered Bi₂O₃ pellets by sulfurizing them in H₂S atmosphere. The direct band-gap and indirect band-gap of Bi₂S₃ were evaluated as 1.2 and 0.4 eV, respectively. A high incident photon to current conversion efficiency in the near IR region was observed on Bi₂S₃|Bi₂O₃ electrodes. Photocurrent generation of Bi₂S₃|Bi₂O₃ electrodes was explained from the viewpoint of semiconductor sensitization. The flat band potential of Bi₂S₃ was evaluated as −1.1 V vs. Ag|AgCl in aqueous polysulfide redox electrolyte (1 M OH⁻, 1 M S²⁻, 10⁻² M S).     

Photocatalytic hydrogen generation in the presence of glucose over ZnS-coated ZnIn2S4 under visible light irradiation

ZnS coated ZnIn₂S₄ (ZnS–ZnIn₂S₄) photocatalysts were prepared in methanol by a facile solvothermal process. The photocatalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), UV–Vis diffusive reflectance spectroscopy (DRS), BET, and electrochemistry measurements. ZnS–ZnIn₂S₄ photocatalysts have hexagonal crystal phase and complex morphology such as micro-spheres, micro-tubes and micro-ribbons. Using glucose as an electron donor, photocatalytic hydrogen generation over Pt/ZnS–ZnIn₂S₄ was investigated. The results show that photoactivity of hydrogen generation over Pt/ZnS–ZnIn₂S₄ was improved notably with simultaneous degradation of glucose. The factors which affect photocatalytic hydrogen generation, such as composition of ZnS-ZnIn₂S₄, initial concentration of glucose and concentration of NaOH, were investigated. The prepared ZnS–ZnIn₂S₄ photocatalysts exhibit better activity for hydrogen generation than pure ZnIn₂S₄, which may be attributed to enhancement of the adsorption of glucose by ZnS on the ZnIn₂S₄ surface. The effect of glucose concentration on the hydrogen generation rate is consistent with a Langmuir model. The basic condition is favorable for the photocatalytic hydrogen generation. A large number of ·OH radicals generated in ZnS–ZnIn₂S₄ system, have been tested by a TA-FL (terephthalic acid-fluorescence) method. A possible mechanism was discussed.     

Sonochemistry synthesis of Bi2S3/CdS heterostructure with enhanced performance for photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution from water splitting is an efficient, eco-friendly method for the conversion of solar energy to chemical energy. A great number of photocatalysts have been reported but only a few of them can respond to visible-light. Metal sulfides, a class of visible-light response semiconductor photocatalysts for hydrogen evolution and organic pollutant degradation, receive a lot of attention due to their narrow band gaps. Herein, we report the sonochemical synthesis of Bi₂S₃/CdS nanocrystal composites with microsphere structure at mild temperature. The phases of Bi₂S₃ and CdS can be observed obviously in HRTEM image. The heterostructure consisting of the two species of nanocrystals plays a key role in separating photo-generated charge carriers. Photocatalytic activities for water splitting are investigated under visible-light irradiation (λ > 400 nm) and an enhanced photocatalytic activity is achieved. The initial rate of H₂ evolution is up to 5.5 mmol h⁻¹ g⁻¹ without resorting to any cocatalysts.     

CuInS2/In2S3 thin film solar cell using spray pyrolysis technique having 9.5% efficiency

Copper indium sulfide (CuInS₂)/In₂S₃ solar cells were fabricated using spray pyrolysis method and high short circuit current density and moderate open circuit voltage were obtained by adjusting the condition of deposition and thickness of both the layers. Consequently, a relatively high efficiency of 9.5% (active area) was obtained without any anti-reflection coating. The cell structure was ITO/CuInS₂/In₂S₃/Ag. We avoided the usual cyanide etching and CdS buffer layer, both toxic, for the fabrication of the cell.     

Improving photocatalytic activity for hydrogen evolution over ZnIn2S4 under visible-light: A case study of rare earth modification

A series of rare earth (RE) ions (La³⁺, Ce³⁺, Gd³⁺, Er³⁺ or Y³⁺) modified ZnIn₂S₄ photocatalysts (RE-ZnIn₂S₄) were prepared using the hydrothermal method and characterized by various analysis techniques, such as UV–Vis diffusive reflectance spectroscopy, X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller surface analyzer, photoluminescence spectroscopy and X-ray photoelectron spectroscopy. The results indicated that the RE element exists as the oxide RE₂O₃ and their modification can reduce ZnIn₂S₄ crystallite size, inhibit ZnIn₂S₄ grain growth, promote ZnIn₂S₄ crystallite self-organization into a micro-sphere flower-like morphology, increase ZnIn₂S₄ surface area and total pore volume, and bring rich defects to ZnIn₂S₄. The photocatalytic activities of RE-ZnIn₂S₄ were evaluated based on photocatalytic hydrogen production from water under visible-light irradiation and the hydrogen production efficiency increased by 46%, 53%, 61%, 69%, and 106% after adding 2.0 wt% of Y, Gd, Er, Ce and La, respectively. The relationship between the photocatalytic activity of RE-ZnIn₂S₄ and the RE properties was discussed.