Effects of step-deposition on structures and properties of transparent conducting aluminum-doped zinc oxide films prepared by DC magnetron sputtering

The 2 wt% aluminum-doped zinc oxide films (AZO) was sputtered on corning glass plate at temperatures of 30–200 °C by DC magnetron sputtering using ceramic target. The microstructures and electrical resistivity of thin films were investigated by scanning electron microscope (SEM) and the van der Pauw method. The optical transmittances of films were measured by UV visible spectrophotometer in the wavelength of 300–900 nm. It was found that the average optical transmittances of specimens were 88%. Highly oriented AZO films in the (0 0 2) direction was observed in specimens as increasing of the substrate temperature. The dense film increased as the temperature increases. In addition, craters of greater depth with more compactness were obtained by step-deposition. The lowest resistivity of 9×10⁻⁴ Ω cm with film thickness of 700 nm was found in specimen grown by step-deposition at 200 °C.     

Energy-saving transparent heat mirrors based on tungsten oxide–gold WO3/Au/WO3 multilayer structures

Transparent heat mirrors are multilayer structures that transmit visible light while reflecting infrared heat. Heat mirrors based on tungsten oxide and gold multilayers WO₃/Au/WO₃ were fabricated by thermal evaporation, and their performance was investigated as a function of the thickness of the gold layer. First, the properties of individual layers were investigated. Atomic force microscopy revealed that all layers possessed smooth surfaces that were suitable for optical applications. The transmittance of the gold layers was found to decrease as the thickness is increased, with an opposite trend followed by infrared reflectance. In the multilayers, the thickness of the WO₃ was fixed at 34 nm, whereas the thickness of the gold layers was varied in the range 20–44 nm. X-ray photoelectron spectroscopy was used to investigate the elemental diffusion among the various layers, and it revealed the presence of inter-diffusion of elements throughout the layers. The performance of the heat mirrors was evaluated on the basis of their optical behavior. The optimum thickness of the gold layer was found to be 36 nm, with a peak spectral transmittance of 84%.     

Electrodeposited tin selenide thin films for photovoltaic applications

Tin selenide thin films of about 300 nm thickness were electrodeposited on SnO₂:F coated transparent conductive oxide glass substrates. The optimum deposition potential was determined from cyclic voltammetry measurements. The films were polycrystalline with orthorhombic structure and the grain size was about 18 nm. SEM images showed a highly porous film structure. The band gap estimated from optical spectra of these films showed absorption due to direct transition occurring at 1.1 eV. Characteristic vibrational modes of the SnSe were observed in the Raman spectrum. The films are p-type, photosensitive, and the conductivity measured in dark was in the range of 10^?5 Ω^?1 cm^?1. A prototype CdS/SnSe photovoltaic device showed an open circuit voltage of 140 mV and short circuit current density 0.7 mA/cm².     

A novel Al and Y codoped ZnO/n-Si heterojunction solar cells fabricated by pulsed laser deposition

Al and Y codoped ZnO (AZOY) transparent conducting oxide (TCO) thin films were first deposited on n-Si substrates by pulsed laser deposition (PLD) to form AZOY/n-Si heterojunction solar cells. However, the properties of the AZOY emitter layers are critical to the performance of AZOY/n-Si heterojunction solar cells. To estimate the properties of AZOY thin films, films deposited on glass substrates with various substrate temperatures (T_s) were analyzed. Based on the experimental results, optimal electrical properties (resistivity of 2.8 ± 0.14 × 10^?4 Ω cm, carrier mobility of 27.5 ± 0.55 cm²/Vs, and carrier concentration of 8.0 ± 0.24 × 10²⁰ cm^?3) of the AZOY thin films can be achieved at a T_s of 400 °C, and a high optical transmittance of AZOY is estimated to be >80% (with glass substrate) in the visible region under the same T_s. For the AZOY/n-Si heterojunction solar cells, the AZOY thin films acted not only as an emitter layer material, but also as an anti-reflected coating thin film. Thus, a notably high short-circuit current density (J_sc) of 31.51 ± 0.186 mA/cm² was achieved for the AZOY/n-Si heterojunction solar cells. Under an AM1.5 illumination condition, the conversion efficiency of the cells is estimated at only approximately 4% (a very low open-circuit voltage (V_oc) of 0.24 ± 0.001 V and a fill factor (FF) of 0.51 ± 0.011) without any optimization of the device structure.     

Wide-optical bandgap with improved conductivity p-μc-Si:Ox:H films prepared by Cat-CVD

Boron-doped hydrogenated microcrystalline silicon oxide (p-μc-Si:O_x:H) films have been deposited using catalytic chemical vapor deposition (Cat-CVD). The single-coiled tungsten catalyst temperature (T_fil) was varied from 1850 to 2100 °C and films were deposited on glass substrates at the temperatures (T_sub) of 100–300 °C. Different catalyst-to-substrate distances of 3–5 cm and deposition pressures from 0.1 to 0.6 Torr were considered.Optical and electrical characterizations have been made for the deposited samples. The sample transmittance measurement shows an optical-bandgap (Eg_opt) variation from 1.74 to 2.10 eV as a function of the catalyst and substrate temperatures. One of the best window materials was obtained at T_sub=100 °C and T_fil=2050 °C, with Eg_opt=2.10 eV, dark conductivity of 3.0×10^?3 S cm^?1 and 0.3 nm s^?1 deposition rate.     

Band gap engineering of RF-sputtered CuInZnSe2 thin films for indium-reduced thin-film solar cell application

We demonstrated the preparation and characterization of radio frequency (RF)-sputtered CuInZnSe₂ thin films for indium-reduced thin-film solar cell application. Sputtering targets composed of high-purity CuSe, InSe and ZnSe powders were employed for preparing CuInZnSe₂ films with various band gaps. Under an optimum condition, an increase of zinc concentration in the film could reduce indium approximately to 45%. The structure of the films showed a chalcopyrite phase with a predominant (1 1 2) reflection. The p-type CuInZnSe₂ films exhibited a shift of optical transmittance to a lower wavelength and the band gap could be engineered from 1.0 to 1.25 eV in proportion with increasing zinc concentration.     

Electronic structure and water splitting under visible light irradiation of BiTa1−xCuxO4 (x = 0.00–0.04) photocatalysts

A series of photocatalysts, BiTa_1?xCu_xO₄ (x = 0.00–0.04), were synthesized by the conventional solid-state reaction method and their electronic structures and photocatalytic activities were investigated. The electron microscope observations revealed that the particle sizes of BiTaO₄:Cu crystals were smaller and the surface with many characteristic steps was more obvious than that of the nondoped BiTaO₄, which lead to the increase of photocatalytic activity of water splitting. The UV–vis spectra indicate that the Cu²⁺ ions doping not only enhanced the photocatalytic activity under ultraviolet–visible (λ > 300 nm) light irradiation but also induced the visible light (λ > 400 nm) response. The photocatalyst doped with 2 mol% Cu²⁺ and loaded with 0.3 wt% RuO₂ co-catalyst was found to have the highest activity. New band gap in the visible light range is obtained by copper-doped BiTaO₄, which is attributed to the transition from the donor level resulting from the Cu impurity to the conduction band of BiTaO₄ doped with copper on the basis of the result of DFT calculation.     

Fabrication and characterisations of n-CdS/p-PbS heterojunction solar cells using microwave-assisted chemical bath deposition

n-CdS/p-PbS heterojunction solar cells were prepared via microwave-assisted chemical bath deposition method. A cadmium sulfide (CdS) window layer (340 nm thickness) was deposited on an indium tin oxide (ITO) glass. A lead sulfide (PbS) absorber layer (985–1380 nm thickness) with different molar concentrations (0.02, 0.05, 0.075, and 0.1 M) was then grown on ITO/CdS to fabricate a p–n junction. The effects of changing molar concentration of the absorber layer on structural and optical properties of the corresponding PbS thin films and solar cells were investigated. The optical band gap of the films decreased as the molarity increased. The photovoltaic properties (J–V characteristics, short circuit current, open circuit voltage, fill factor, and efficiency) of the CdS/PbS heterostructure cells were examined under 30 mW/cm² solar radiation. Interestingly, changing molar concentration improved the photovoltaic cells performances, the solar cell exhibited its highest efficiency (1.68%) at 0.1 M molar concentration.     

Nanocrystalline tin oxides and nickel oxide film anodes for Li-ion batteries

Tin oxides and nickel oxide thin film anodes have been fabricated for the first time by vacuum thermal evaporation of metallic tin or nickel, and subsequent thermal oxidation in air or oxygen ambient. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements showed that the prepared films are of nanocrystalline structure with the average particle size <100 nm. The electrochemical properties of these film electrodes were examined by galvanostatic cycling measurements and cyclic voltammetry. The composition and electrochemical properties of SnO_x (1<x<2) films strongly depend on the oxidation temperature. The reversible capacities of SnO and SnO₂ films electrodes reached 825 and 760 mAh g⁻¹, respectively, at the current density of 10 μA cm⁻² between 0.10 and 1.30 V. The SnO_x film fabricated at an oxidation temperature of 600 °C exhibited better electrochemical performance than SnO or SnO₂ film electrode. Nanocrystalline NiO thin film prepared at a temperature of 600 °C can deliver a reversible capacity of 680 mAh g⁻¹ at 10 μA cm⁻² in the voltage range 0.01–3.0 V and good cyclability up to 100 cycles.     

Structural characterization and electrochemical properties of RF-sputtered nanocrystalline Co3O4 thin-film anode

Nanocrystalline Co₃O₄ thin-film anodes were deposited on Pt-coated silicon and 304 stainless steel by radio frequency (RF) magnetron sputtering. The as-deposited and annealed cobalt oxide thin films showed smooth and crack-free morphologies. Both the as-deposited and annealed films exhibited spinel Co₃O₄ phase with nanocrystalline structure. High-temperature annealing enhanced the crystallinity of RF-sputtered cobalt oxide films due to rearrangement of cobalt and oxygen atoms. Electrochemical characterization of RF-sputtered films was carried out by cyclic voltammetry and charge/discharge tests in the voltage range of 0.3–3.0 V. Cyclic voltammetry plots showed that the RF-sputtered Co₃O₄ thin films were electrochemically active. X-ray photoelectron spectrometer (XPS) showed that the fresh cobalt oxide films had two peaks of Co₃O₄. In addition to the binding energy of cobalt oxide, the XPS spectrum of discharged film presented two additional binding energies correspond to Co metal. The first discharge capacities of as-deposited, 300, 500, and 700 °C-annealed films were 722.8, 772.5, 868.4, and 1059.9 μAh cm⁻² μm⁻¹, respectively. High-temperature annealing could enhance the capacity and cycle retention obviously. After 25 cycles discharging, the annealed films showed better cycle retention than as-deposited film. The 700 °C-annealed film exhibited excellent discharge capacity approximated to the theoretical capacity.     

Characterization of polymer electrolytes based on poly(dimethyl siloxane-co-ethylene oxide)

The usefulness of poly(dimethyl siloxane-co-ethylene oxide) (P(DMS-co-EO)) copolymer as an ion conducting matrix was investigated. The electrochemical properties were studied by electrochemical impedance spectroscopy and cyclic voltammetry. The glass transition temperature (T_g) and degree of crystallization as a function of salt concentration were examined by differential scanning calorimetry. Ionic conductivities as high as 2.6×10⁻⁴ S cm⁻¹ were determined at 25 °C for copolymers films with 5 wt.% LiClO₄. These same films had an electrochemical stability window of 5 V. The pseudo-activation energy as a function of salt concentration was obtained using the Vogel–Tamman–Fulcher (VTF) equation.     

Band gap optimization of p–i–n layers of a-Si:H by computer aided simulation for development of efficient solar cell

The p-layer band gap and its thickness strongly influence the efficiency of hydrogenated amorphous silicon (a-Si:H) p–i–n solar cell, i and n-layer band gaps also play key role. In the present work, p, i and n layer band gaps as 2.1 eV (at thickness 10 nm), 1.75 eV (at thickness 400 nm) and 1.95 eV (at thickness 30 nm), respectively and acceptor and donor concentrations as 1 × 10¹⁸ cm^?3and 1 × 10²⁰ cm^?3, respectively, are optimized for obtaining efficient a-Si:H p–i–n solar cell by computer aided one-dimensional AFORS-HET software. It is important to mention that when p-layer thickness is changed to 5 nm, maximum efficiency is obtained at p-layer band gap of 2.2 eV. Such an optimized value would further help to prepare efficient a-Si:H p–i–n solar cells experimentally.     

The study of preparation and photoelectrical properties of chemical bath deposited Zn,Sb and Ni-doped CuInS2 films for hydrogen production

Pure and Zn, Sb, Ni-doped CuInS₂ films were prepared by chemical bath deposition method. Structural, morphological, optical, and photoelectrochemical properties of the as-grown films were investigated. X-ray diffraction analysis revealed that films consisted of the tetragonal CuInS₂ phase. The energy band gaps and carrier densities of these samples were in the ranges of 1.48–1.54 eV and 2.38 × 10¹⁸–9.38 × 10¹⁹, respectively. The maximum photocurrent density of samples with a potential of ?1.0 V vs. a Pt electrode was found to be ?8.58 mA/cm² with the largest hydrogen production capability of 33.26 μmol/cm² under illumination using a 300 W Xe lamp system.     

Opportunity of metallic interconnects for ITSOFC: Reactivity and electrical property

Iron-base alloys (Fe–Cr) are proposed hereafter as materials for interconnect of planar-type intermediate temperature solid oxide fuel cell (ITSOFC); they are an alternative solution instead of the use of ceramic interconnects. These steels form an oxide layer (chromia) which protects the interconnect from the exterior environment, but is an electrical insulator. One solution envisaged in this work is the deposition of a reactive element oxide coating, that slows down the formation of the oxide layer and that increases its electric conductivity. The oxide layer, formed at high temperature on the uncoated alloys, is mainly composed of chromia; it grows in accordance with the parabolic rate law (k_p = 1.4 × 10⁻¹² g² cm⁻⁴ s⁻¹). On the reactive element oxide-coated alloy, the parabolic rate constant, k_p, decreases to 1.3 × 10⁻¹³ g² cm⁻⁴ s⁻¹. At 800 °C, the area-specific resistance of Fe–30Cr alloys is about 0.03 Ω cm² after 24 h in laboratory air under atmospheric pressure. The Y₂O₃ coating reduces the electrical resistance 10-fold. This indicates that the application of Y₂O₃ coatings on Fe–30Cr alloy allows to use it as an interconnect for SOFC.     

Investigations on microstructural and optical properties of CdS films fabricated by a low-cost,simplified spray technique using perfume atomizer for solar cell applications

Good quality CdS films were fabricated by employing a simplified spray pyrolysis technique using perfume atomizer. CdS films have been deposited from aqueous solutions of sulphur and cadmium, keeping the molar concentrations of S:Cd = 0.01:0.01, 0.02:0.02, 0.04:0.04 and 0.06:0.06 in the starting solutions. The structural studies reveal that the S:Cd concentration has a strong influence on the microstructural characteristics of the sprayed CdS films. It was found that there is a transition in the preferred orientation from (0 0 2) plane to (1 0 1) plane when S:Cd molar concentration increases. The SEM images depict that the films are uniform and homogeneous. All the films have high optical transmittance (>80%) in the visible range. The optical band gap values are found to be in the range of 2.46–2.52 eV. CdS films fabricated by this simple and economic spray technique without using any carrier gas are found to be good in structural and optical properties which are desirable for photovoltaic applications. Hence, this simplified version of spray technique can be considered as an economic alternative to conventional spray pyrolysis (using carrier gas), for the mass production of low-cost, large area CdS coatings for solar cell applications.     

Synthesis,structural and electrochemical properties of pulsed laser deposited Li(Ni,Co)O2 films

We report the epitaxial growth of the LiNi_1−yM_yO₂ films (M = Co, Co–Al) on heated nickel foil using pulsed laser deposition in oxygen environment from lithium-rich targets. The structure and morphology was characterized by X-ray diffractometry, electron scanning microscopy and Raman spectroscopy. Data reveal that the formation of oriented films is dependent on two important parameters: the substrate temperature and the gas pressure during ablation. The charge–discharge process conducted in Li-microcells demonstrates that effective high specific capacities can be obtained with films 1.35 μm thick. Stable capacities of 83 and 92 μAh cm⁻² μm are available in the potential range 4.2–2.5 V for LiNi_0.8Co_0.2O₂ and LiNi_0.8Co_0.15Al_0.05O₂ films, respectively. The self-diffusion coefficient of Li ions determined from galvanostatic intermittent titration experiments is found to be 4 × 10⁻¹² cm² s⁻¹.     

Polymer Ni–MH battery based on PEO–PVA–KOH polymer electrolyte

An alkaline polymer electrolyte film has been prepared by a solvent-casting method. Poly(vinyl alcohol), PVA is added to improve the ionic conductivity of the electrolyte. The ionic conductivity increases from 10⁻⁷ to 10⁻² S cm⁻¹ at room temperature when the weight percent ratio of poly(ethylene oxide), PEO to PVA is increased from 10:0 to 5:5. The activation energy of the ionic conductivity for the PEO–PVA–KOH polymer electrolyte is 3–8 kJ mol⁻¹. The properties of the electrolyte film are characterized by a wide variety of techniques and it is found that the film exhibits good mechanical stability and high ionic conductivity at room temperature. The application of such electrolyte films to nickel–metal-hydride (Ni–MH) batteries is examined and the electrochemical characteristics of a polymer Ni–MH battery are obtained.     

Physical properties of the CNT:TiO2 thin films prepared by sol–gel dip coating

Uniform and highly adherent thin films of CNT:TiO₂ were synthesized by sol–gel dip coating method. Both TiO₂ and CNT:TiO₂ films showed very identical structural characteristics and no significant changes in the lattice values were observed. The crystalline size decreased from 20 nm for TiO₂ film to 17 nm for the 4%CNT:TiO₂ film. The film surface was very smooth and compact, as indicated by the roughness data obtained from AFM measurements; the root mean square (rms) average of the roughness was as low as 3 nm. The HRTEM showed that the CNTs are embedded in the matrix of TiO₂ indicating the formation of a composite. In Raman spectra the characteristic vibrations of the TiO₂ are identified, the increase in the FWHM of main anatase peak (144 cm^?1) in the case of the 4%CNT:TiO₂ film is interpreted as due to the incorporation of CNTs in the film. At the wavelength of 600 nm the refractive index of pure TiO₂ was 2.07 and the 4%CNT:TiO₂ showed a value of 2.29. The photoresponse curves showed typical features of charge trapping centers in the band gap of the films.     

Experimental investigation on non-Newtonian behavior of Al2O3-MWCNT/5W50 hybrid nano-lubricant affected by alterations of temperature,concentration and shear rate for engine applications

In the present study, rheological behavior of Al₂O₃-MWCNT (65%–35%)/5W50 hybrid nano-lubricant is experimentally evaluated with the aim of facilitating its applications in automotive industry. Aluminum oxide (Al₂O₃) nanoparticles with the mean diameter of 50 nm along with multi-walled carbon nanotubes (MWCNTs) with inner diameter of 3–5 nm and outer diameter of 5–15 nm were used as nano-dispersants. Dynamic viscosity of samples of hybrid nano-lubricant composed out of 0% up to 1% solid volume fraction was measured at temperatures between 5 and 55 °C and shear rates between 666.5 and 10,664 s^− 1. As a result it was revealed that the hybrid nano-lubricant is a non-Newtonian fluid, also power law index signified shear thinning (pseudoplastic) behavior of the fluid. It was observed that increasing of solid volume fraction aggravates non-Newtonian behavior of the nano-lubricant; on the contrary, temperature increment had the reverse effect. For the purpose of forecasting viscosity of the hybrid nano-lubricant, a new correlation is proposed which is based on temperature and solid volume fraction. R-squared of the correlation outputs is 0.9923, this means that the correlation is capable of modeling viscosity behavior of the hybrid nano-lubricant.     

P(DMS-co-EO)/P(EPI-co-EO) blend as a polymeric electrolyte

A new polymer electrolyte comprising the blend of poly(dimethylsiloxane-co-ethylene oxide) (P(DMS-co-EO)), and poly(epichlorohydrin-co-ethylene oxide) (P(EPI-co-EO)), with different concentrations of LiClO₄ is described. The polymer electrolyte was prepared by a solution-cast technique. The electrochemical properties were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry techniques. The maximum ionic conductivity (σ=1.2×10⁻⁴ S cm⁻¹) was obtained for the P(DMS-co-EO)/P(EPI-co-EO) 15/85 and 20/80 blends with 6 wt.% LiClO₄. These same films had a wide electrochemical stability, higher than 5 V at room temperature. A stable passive layer at the interface between the polymer electrolyte and lithium metal was formed within the first few days and maintained during the follow storage period. UV-Vis absorption spectra of the blends showed a transparent polymer electrolyte in the visible region.