Shape and size controlled synthesis of CuInS<Subscript>2</Subscript> particles in polyalcohol system used as “printable ink” for thin films

Chalcopyrite semiconductor CuInS₂ (CIS) particles are synthesized using a simple method and low-cost solvent. Two kinds of agents are used to adjust and control the sizes and shapes of the particles. The phases, morphologies and grown processes of the products are studied. The results show that the sizes and shapes of the CIS particles can be adjusted and controlled. Furthermore, CIS thin films are fabricated using these two kinds of particles. The thin films appear different morphologies and qualities via different kinds of particles, indicating the importance of controlling the shape and size of the precursor particles.     

Synthesis and characterization of CuInS<Subscript>2</Subscript> nanoflowers

Uniform crystalline CuInS₂ nanoflowers with an average size of 25 nm were synthesized by a hot-injection strategy using CuAc, In(Ac)₃ and sulfur powder as precursors and oleylamine as both the solvent and ligand. Various methods including X-ray diffraction, transmission electron microscopy and absorption spectroscopy were used to characterize CuInS₂ nanoflowers. Control experiments indicated that CuInS₂ nanoflowers were formed through 3D attachment of forming primary nanodots. The obtained CuInS₂ nanoflowers are promising for low-cost, high efficiency solar cells due to several advantages such as the simplicity of synthesis, size and morphology uniformity, stability of dispersion and large surface area for charge separation.     

Hydrothermal synthesis of brookite TiO<Subscript>2</Subscript> nanoparticles for dye-sensitized solar cell

We obtained Tannin-4-azobenzoic acid (azo dye) by the conventional method of diazotization and coupling of aromatic amines. The properties of the azo dye were characterized via ultraviolet-visible (UV–vis), infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy. Nanocrystalline titanium dioxide (TiO₂) thin films were deposited by hydrothermal method onto fluorine-doped tin (IV) oxide (FTO)-coated glass substrate at 353 K for 4 h. The as-deposited and annealed films were characterized for structural, morphological, optical, thickness, and wettability properties. The synthesized metal free azo dye was used to sensitize the prepared TiO₂ thin film with thickness of 26 μm. The photoelectrochemical (PEC) performance of TiO₂ sensitized with the azo dye was evaluated in polyiodide (0.1 M KI + 0.01 M I₂ + 0.1 M KCl) electrolyte at 40 mW cm^?2 illumination intensity. The cell yielded a short circuit current of 2.82 mA, open circuit voltage of 314.3 mV, a fill factor of 0.30, and a photovoltaic conversion efficiency value of 0.64%.

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Electrodeposition of thin Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> films

The electrochemical behavior of copper(II), zinc(II), and thiosulfate (S₂O₃ ^2-) ions on the molybdenum electrode in individual 0.2 М sodium sulfate solutions (рН 6.7) and with addition of either 0.1 М tartaric acid (рН 4.6) or 0.1 М citric acid (рН 4.7) is studied. A one-step electrochemical method is developed for the deposition of thin Cu₂ZnSnS₄ films, which is carried out on the molybdenum electrode at a constant potential in sodium sulfate solutions containing tartaric acid. The effect of the concentration of electrolyte components on the chemical composition of Cu₂ZnSnS₄ films is determined. The phase composition is confirmed by the Raman spectroscopy data. The surface morphology of synthesized films is studied by means of scanning-electron and atomic-force microscopes. The photoelectrochemical characteristics of Cu₂ZnSnS₄ films are determined. Samples of these coatings on the Mo electrode are found to be highly photosensitive.     

Synthesis and characterization of ZrO<Subscript>2</Subscript> thin films

Physicochemical processes involved in the preparation of zirconia thin films by sol-gel technology from film-forming solutions (FFSs) on the basis of zirconium oxochloride and ethanol were studied. The phase composition, structure, and properties of the films were determined.     

Electrodeposition of CuGaSe<Subscript>2</Subscript> and CuGaS<Subscript>2</Subscript> thin films for photovoltaic applications

CuGaSe₂ and CuGaS₂ polycrystalline thin film absorbers were prepared by one-step electrodeposition from an aqueous electrolyte containing CuCl₂, GaCl₃ and H₂SeO₃. The pH of the solution was adjusted to 2.3 by adding HCl and KOH. Annealing improved crystallinity of CuGaSe₂ and further annealing in sulphur atmosphere was required to obtain CuGaS₂ layers. The morphology, topography, chemical composition and crystal structure of the deposited thin films were analysed by scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy and X-ray diffraction, respectively. X-Ray diffraction showed that the as-deposited CuGaSe₂ film exhibited poor crystallinity, but which improved dramatically when the layers were annealed in forming gas atmosphere for 40 min. Subsequent sulphurization of CuGaSe₂ films was performed at 400 °C for 10 min in presence of molecular sulphur and under forming gas atmosphere. The effect of sulphurization was the conversion of CuGaSe₂ into CuGaS₂. The formation of CuGaS₂ thin films was evidenced by the shift observed in the X-ray diffraction pattern and by the blue shift of the optical bandgap. The bandgap of CuGaSe₂ was found to be 1.66 eV, while for CuGaS₂ it raised up to 2.2 eV. A broad intermediate absorption band associated to Cr and centred at 1.63 eV was observed in Cr-doped CuGaS₂ films.     

Characterization of nanocrystalline anatase TiO<Subscript>2</Subscript> thin films

Nanoporous thin films were deposited onto glass substrates by painting with a solution of nanocrystalline anatase TiO(2) particles (with a size of either 6 nm or 16 nm) suspended in an organic solvent. Upon drying in air for about 1 day, the films were tempered at 450 degrees C in air for 1 h. This procedure results in stoichiometric TiO(2) films with a thickness of several micro m and a milky whitish appearance. Scanning force microscopy of the surface revealed that the nanoparticles of the films agglomerated into structures with lateral dimensions of some 100 nm. Transmission electron microscopy was utilized to investigate the structural arrangement of the crystallites in the films. High-resolution electron diffraction and X-ray diffraction analyses demonstrated, furthermore, that the material consists exclusively of a single TiO(2) phase, namely anatase, and that the films do not exhibit any preferential texture. The elemental stoichiometry and the possible presence of impurities were monitored throughout the films by means of secondary-ion mass spectrometry depth profiling. Electrical measurements have been carried out as a function of both the sample temperature T and the ambient oxygen partial pressure p(O(2)). From these data the electrical conductivity sigma of the porous films was determined in dependence of those parameters.     

Modification of TiO<Subscript>2</Subscript> electrode films in dye-sensitized solar cells with PMMA

Nanocrystalline porous TiO₂ electrodes for dye-sensitized solar cells (DSC) are modified by adding polymethyl methacrylate (PMMA). The result shows that large holes are formed in the TiO₂ films, and the short circuit photocurrent density and photoelectric conversion efficiency of DSCs are obviously enhanced compared with those without adding the PMMA. The relationship between the photoelectric conversion efficiency and the amount of PMMA is presented. In particular, the highest conversion efficiency was obtained with TiO₂ electrode films of adding 7.5 wt% PMMA, increasing the conversion efficiency by 27.5%.     

Physicochemical processes involved in synthesis of thin films based on double oxides of the ZrO<Subscript>2</Subscript>-GeO<Subscript>2</Subscript> system

The major physicochemical processes underlying the preparation of thin films of the ZrO-GeO₂ system from film-forming solutions based on zirconium oxochloride (ZrOCl₂ · 8H₂O), germanium tetrachloride (GeCl₄), and ethanol were studied. The phase composition, structure, and physicochemical properties of the films were determined.     

Stability of CdS-coated TiO<Subscript>2</Subscript> solar cells

The obstacle to realize the large-scale production of dye-sensitized solar cells (DSSCs) is its long-term stability and reliability problem. One of the main causes of the instability of DSSCs is the use of liquid electrolytes. In addition, exploring nano-sized particles of CdS as an alternative sensitizer for organic dye in dye-sensitized solar cells have attracted great interest due to the high cost and the instability of the organic dye. Our study has found that the CdS-coated TiO₂ cell degrades rapidly in the liquid electrolytes even under dark environment. In this work, a solid-state solar cell structure of Glass/FTO/TiO₂/CdS:Cu/FTO/glass was successfully made with an efficiency of 0.7%. CdS:Cu served as both the p-type conductor and absorber. No efficiency was obtained for cell structures of glass/FTO/TiO₂/CdS/FTO/glass. This indicates the effectiveness of hole conducting behavior of CdS:Cu. This is the first time that this type of solid-state solar cell is reported and improved stability is demonstrated.     

Light conversion efficiency of flower like structure TiO<Subscript>2</Subscript> thin film solar cells

Flower like structure TiO₂ thin films have been grown onto ITO coated glass substrates by sol–gel method. TiO₂ nano flowers have been sensitized using CdS quantum dots prepared using simple precursors by chemical method. The assembly of CdS quantum dots with TiO₂ nano flower has been used as photo-electrode in quantum dot sensitized solar cells. The surface morphology has been studied using scanning electron microscope; it shows that the film exhibits flower like structure. The absorption spectra reveals that the absorption edge of CdS quantum dot sensitized TiO₂ nano flower shifts towards longer wavelength side when compared to the absorption edge of TiO₂ nano flower. The efficiency of the fabricated CdS quantum dot sensitized TiO₂ nano flower based solar cell is 0.66%.     

Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

Photoelectrochemical study of electrodeposited TiO<Subscript>2</Subscript> thin films onto F:SnO<Subscript>2</Subscript> substrates

TiO₂ thin films have been effectively fused onto F:SnO₂ (FTO) substrates via the electrodeposition method. The influence of deposition temperature on the synthesis of F:SnO₂ substrates and relative information of as-deposited and annealed TiO₂ thin films have been studied. Novel TiO₂ microspheres are detected on F:SnO₂ substrates at an optimized electrodeposition potential. Raman bands approve the creation of single-anatase-phase TiO₂. The optimized deposition surroundings show a decrease in the band gap of F:SnO₂ substrates and TiO₂ thin films. The determined photoelectrochemical properties of annealed TiO₂ thin films indicate a fill factor of 51% and power conversion efficiency of 0.15% for application in solar cells.     

In situ synthesis of plate-like Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in porous cellulose films with obvious magnetic anisotropy

Nanocomposite cellulose films with obvious magnetic anisotropy have been prepared by in situ synthesis of plate-like Fe₂O₃ nanoparticles in the cellulose matrix. The influence of the concentrations of FeCl₂ and FeCl₃ solutions on the morphology and particle size of the synthesized Fe₂O₃ nanoparticles as well as on the properties of the composite films has been investigated. The Fe₂O₃ nanoparticles synthesized in the cellulose matrix was γ-Fe₂O₃, and its morphology was plate-like with size about 48 nm and thickness about 9 nm, which was totally different from those reported works. The concentration of FeCl₂ and FeCl₃ solution has little influence on the particle size and morphology of the Fe₂O₃ nanoparticles, while the content of Fe₂O₃ nanoparticles increased with the increase of the concentration of the precursor solution, indicating that porous structured cellulose matrix could modulate the growth of inorganic nanoparticles. The unique morphology of the Fe₂O₃ nanoparticles endowed the composite films with obvious magnetic anisotropy, which would expand the applications of the cellulose based nanomaterials.     

Electrodeposition of thin cadmium sulfide films from Na<Subscript>2</Subscript>SO<Subscript>3</Subscript>-based electrolyte

Results of a study of the electrodeposition of thin cadmium sulfide films from a sulfite electrolyte and its degradation in the course of electrolysis are presented. The factors determining the degradation rate of the electrolyte are revealed. The supposed mechanism of reactions resulting in that CdS is formed is described.     

Preparation of MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles by microemulsion method and their characterization

This work presents the preparation and characterization of magnesium ferrite which is one of the important magnetic oxides with spinel structure. Magnesium ferrite was prepared via microemulsion method mediated hydrolytic decomposition of mixed alkoxide solutions. This microemulsion was using for preparation magnesium ferrit for the first time. The starting solution, composed from magnesium methoxide and iron ethoxide in dry ethanol, was introduced in to the prepared microemulsion and sequentially hydrolyzed by distilled water addition (Pithan et al. in J Cryst Growth 280:191–200, 2005; Shiratori et al. in J Eur Ceram Soc 25:2075–2079, 2005; Herrig and Hempelmann in Mater Lett 27:287–292, 1996). After raw powder precipitation, the samples were decantanted by ethanol and then calcined at temperatures 800, 900, 1,000 or 1,100 °C for 1 h. The resulting samples were characterized using powder X-ray diffraction, high resolution transmission electron microscopy, Mössbauer spectroscopy and magnetic measurements. X-ray diffraction and Mössbauer spectroscopy confirmed the presence of the spinel phase. The particles size was calculated from the XRD line broadening using Scherrer equation and their size was found about 31–38 nm, with only slight dependence on the heat treatment temperature. TEM revealed the particles size of about 39 nm. Magnetic measurements showed a ferrimagnetic behavior for all samples.     

Microstructure of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> hybrid electrospun nanofibers and their application in dye degradation

SiO₂/TiO₂ hybrid nanofibers were prepared by electrospinning and applied for photocatalytic degradation of methylene blue (MB). The phase structure, specific surface area, and surface morphologies of the SiO₂/TiO₂ hybrid nanofibers were characterized through thermogravimetry (TG), X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), etc. XRD measurements indicated that doping of silica into TiO₂ nanofibers can delay the phase transition from anatase to rutile and decrease the grain size. SEM and BET characterization proved that silica doping can remarkably enhance the porosity of the SiO₂/TiO₂ hybrid nanofibers. The MB adsorption capacity and photocatalytic activity of the SiO₂/TiO₂ hybrid nanofibers were distinguished experimentally. It was found that, although increased silica doping content could enhance the MB adsorption capacity, the intrinsic photocatalytic activity gradually dropped. The SiO₂ (10 %)/TiO₂ composite nanofibers exhibited the highest MB degradation rate, being superior to SiO₂ (20 %)/TiO₂ or pure TiO₂.