Nanocluster n-CdO thin film by sol-gel for solar cell applications

The nanocluster-CdO film was successfully synthesized by sol-gel method using cadmium acetate and 2-metoxyethanol as starting materials and monoethanolamine as a stabilizer. The structural properties of the CdO film were investigated by atomic force microscopy (AFM). AFM results indicate that the CdO film is consisted of nanoclusters with grain size of 75-85 nm. The optical band gap E_g of nanocluster-CdO film was found to be 2.27 eV. The heterostructure, formed from two semiconductor layers having different optical band gaps, p-Si/n-CdO is prepared as a solar cell device. The electrical properties of the device were characterized by current-voltage and capacitance-conductance-voltage methods. The photovoltaic properties of p-Si/n-CdO device have been investigated. The p-Si/n-CdO heterojunction solar cell shows the best values of V_oc = 0.41 and J_sc = 2.19 mA/cm² under AM1.5 illumination. It is evaluated that this work is useful as a basis for the search of nanomaterial CdO and more competitive p-Si/n-CdO based solar cells, despite the fact that V_oc and J_sc are lower than those reported in the literature.     

Adsorption and desorption characteristics of barium oxide at high temperature

Oxygen-selective adsorbents were prepared by two different methods, hydrothermal and sol-gel methods. The adsorption and desorption characteristics of these adsorbents were compared in terms of stability and sorption capacity. The sorbents prepared by the sol-gel method showed better cyclic stability and higher adsorption capacity than that prepared by the hydrothermal method because the sol-gel method entrapped well the barium peroxide.Relaxation time for adsorption ranged from 4 to 9 min depending on the preparation methods and that for desorption was 6 min regardless of the preparation methods. Breakthrough experiment with the sorbent prepared by the sol-gel method was performed. The adsorption breakthrough curves at 600 °C showed two plateau regions. One was at about 3.5%, and the other was 20%. The first plateau region is related to the sharp transition point of the oxygen adsorption isotherm. Though the relaxation time for adsorption was 6 min, the time required from the end of the first plateau to the beginning of the second plateau was just 2 min. During the desorption, a plateau region at 3.5% of oxygen concentration was observed regardless of the desorption flow rate.     

Effect of sintering temperature on mechanical behaviour and bioactivity of sol-gel synthesized bioglass-ceramics using rice husk ash as a silica source

Bioglass-ceramics with SiO₂-Na₂O-CaO composition was prepared by sol-gel method using rice husk ash as a silica source. Material was sintered at different temperatures ranging from 900 to 1050 °C for 2 h. Phase-formation behaviour, densification characteristics, and mechanical strength of glass-ceramics were investigated. The material sintered at 1000 °C showed a good mechanical strength. Mechanical properties were correlated with microstructural features. Both in vitro bioactivity and biodegradability of sintered material were investigated by incubating in simulated body fluid and Tris buffer solution, respectively. Scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction were used to investigate the surface deposition during body fluid incubation. Both bioactivity and degradability decreased with increase in sintering temperature.     

Microwave-assisted synthesis of SrFe12O19 hexaferrites

Ultra-fine and homogeneous SrFe₁₂O₁₉ hexaferrites were synthesized by a microwave-assisted calcination route. The calcined precursors were prepared by a sol-gel auto-combustion method using Fe(NO₃)₃·9H₂O, Sr(NO₃)₂ and citric acid as starting materials. The structures, powder morphology and magnetic properties of the products were characterized by X-ray diffraction, scanning electron microscope and vibrating sample magnetometer. The results showed that microwaves are helpful to reduce the calcination temperature and shorten the calcination time. The ferrites with saturation magnetization, remanence and intrinsic coercivity of 54.80 emu/g, 29.52 emu/g and 5261 Oe, respectively, were obtained in samples calcined at 800 °C for 80 min.     

Effects of Sb doping on the structure and properties of SnO2 films

Transparent heat-insulating SnO₂ films were prepared on the glass substrate with sol-gel. The effects of Sb doping on the structure and photoelectric properties of the films were investigated. The films were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), Ultraviolet–Visible-Near Infrared Spectrometer (UV-VIS-NIR) and Hall Effect tester. The results show that the doping of Sb did not change the basic crystal structure of the SnO₂ film, but reduced the crystallinity of the film. With the increase of Sb doping, the grain size decreases first and then maintains basically invariable. The sheet resistance of the film decreases first and then increases. The transmittance of the substrate glass coated with this film (hereinafter referred to as the film's transmittance) in the near-infrared region (780–2500 nm) decreases from 92.55% to 60.48%, and increases a little when the doping amount exceeded 11 mol%. And its transmittance of visible light (380–780 nm) fluctuated slightly between about 81% and 86%.     

Microstructure evolution of room-temperature-sputtered ITO films suitable for silicon heterojunction solar cells

Thickness influence on structural, optical and electrical properties of sputtered indium tin oxide (ITO) with thickness ranging from 60 up to 430 nm films has been studied. At the increase of the film thickness crystallinity degree and grain size increased, whereas tensile structural distortion as well as resistivity decreased. It was observed that a microstructure evolution takes place: the initial amorphous layer evolved in polycrystalline phase, with a grain–subgrain surface morphology. Carrier concentration increased at the increase of the film thickness and a general relationship between electrical characteristics and structural distortion has been found. In thinner films larger tensile distortion allowed to include larger amount of interstitial O and/or Sn atoms in the lattice. An appreciable impact of the thickness was also observed on electro-optical properties in terms of changes in energy gap, resistivity and optical absorption. Silicon heterojunction solar cells have been produced and J_sc as high as 33.0 mA/cm² has been obtained.     

Ultrasound-assisted synthesis of ZnO photocatalysts for gas phase pollutant remediation: Role of the synthetic parameters and of promotion with WO3

The synthesis of ZnO photocatalysts by ultrasound-assisted technique was here investigated. Several experimental parameters including the zinc precursor (acetate, chloride, nitrate), sonication conditions (amplitude, pulse) and post-synthetic thermal treatment (up to 500 °C) were studied. Crystalline ZnO samples were obtained without thermal treatments due to the adopted reactant ratios and synthesis temperature. Sonication plays a major role on the morphological oxide features in terms of particle size and surface area, the latter showing a 20-fold increase with respect to conventional synthesis. Interestingly, 1 and 3 s sonication pulses led to morphological properties similar to continuous sonication. A thermal treatment at moderate temperatures (400–450 °C) promoted the loss of surface hydroxylation and the formation of lattice defects, while higher temperatures were detrimental for the sample morphology. The prepared ZnO was decorated with WO₃ particles comparing an ultrasound-assisted technique using 1 s pulses with a conventional approach, giving rise to composites with promoted visible light absorption. Samples were tested towards the photocatalytic degradation of nitrogen oxides (500–1000 ppb) in humidified air under both UV and visible light. By carefully controlling the synthetic procedure, better performance were observed with respect to the commercial benchmark. Samples from ultrasound-assisted syntheses, also in the case of pulsed sonication, showed consistently better results than conventional references, in particular for ZnO-WO₃ composites. The composite by ultrasound-assisted synthesis showed > 95% degradation in 180 min and doubled NO_x degradation under visible light with respect to the conventional composite.     

Cooperative effect of La-doping and template on surface photoelectron characteristics of mesoporous nano-TiO2

A mesoporous La-doped nano-TiO₂ was prepared by the sol-gel method using polyethylene glycol as the template. A combination of surface photovoltaic (SPV) and photoacoustic technologies, aided by laser Raman technology, was used to probe the photoexcited charge transfer transition behaviors in the surface space charge region of the sample. The results confirm that the lanthanum doping was responsible for inhibiting the transformation from the anatase to rutile form and grain growth, thus strengthening the microstructure that was formed after removal of the template clearly. The experiment reveals that appropriate La-doping resulted in an obvious increase in the SPV response. By contrast, the remainder of the template had a somewhat negative effect on the SPV response of the samples. The effect of both the La-doping and the removal of the template on the nonradiative de-excitation process of the main band-gap can be negligible, in spite of the nonradiative de-excitation processes of the sub-band-gap of the La-undoped sample, in which the surface states possessed the donor characteristic, being more obvious than that of the La-doped samples. The results showed that the electron-phonon interactions on the surfaces resulting from the nonradiative de-excitation process were closely dependent on the effect of quantum confinement of the mesoporous nano-TiO₂.     

Ethylene and phenylene bridged polysilsesquioxanes functionalized by amine and thiol groups as adsorbents of volatile organic compounds

Ethylene and phenylene bridged polysilsesquioxane xerogels having amine and thiol groups attached to the surface have been obtained by the sol-gel method from 1,2-bis(triethoxysilyl)ethane or 1,4-bis(triethoxysilyl)benzene and functionalized silanes in the presence of an ammonium fluoride catalyst in an ethanol solution. The synthesized samples have a porous structure (700-850 m²/g) and a high content of functional groups (1.4-1.9 mmol/g). The obtained porous bridged polysilsesquioxanes exhibit a considerable affinity for adsorbing several organic compounds (n-hexane, n-heptane, benzene, cyclohexane, acetonitrile and triethylamine) from the gas phase. The sample with an ethylene bridge and amino groups in the surface layer has the highest uptake of all compounds. Data from adsorption measurements show that functionalized organosilicon materials can be used as effective adsorbents of organic contaminants from the gas phase.