Doughnut-shaped hierarchical Cu2ZnSnS4 microparticles synthesized by cyclic microwave irradiation

For the first time, hierarchical doughnut-shaped Cu₂ZnSnS₄ (CZTS) microparticles were synthesized by microwave-assisted solution method. N,N-dimethylformamide and polyvinylpyrrolidone (PVP) were used as solvent and stabilizing agent respectively, and the results showed that PVP played an important role in the formation of hierarchical nanostructures. Structural analysis by X-ray diffraction and Raman studies confirmed the formation of single phase kesterite CZTS. Morphological analysis by scanning electron microscope showed doughnut-shaped CZTS microparticles composed of large number of interpenetrating nanoplates. Optical analysis by UV–Vis diffused reflectance spectra showed strong absorption in the visible region with an optical band gap of 1.54 eV. Asymmetric broad emission bands around 1.55 eV and 1.30 eV were observed in the photoluminescence spectrum. A possible formation mechanism for doughnut-shaped CZTS microparticles was put forward and discussed briefly.     

Electrochemical behavior of potentiodynamically deposited cobalt oxyhydroxide (CoOOH) thin films for supercapacitor application

In the present study, we report, for the first time, the synthesis of cobalt oxyhydroxide thin films on inexpensive stainless steel substrate using potentiodynamic electrodeposition method. These films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) techniques. The orthorhombic crystal structure was revealed by the X-ray diffraction study. The FT-IR spectrum confirmed the formation of cobalt oxyhydroxide. The SEM studies showed the nanoflakes-like morphology with an average thickness of 100 nm. The cyclic voltammetry study of the cobalt oxyhydroxide films in 1 M KOH showed maximum specific capacitance of 449 F g^?1 at scan rate of 5 mV s^?1.     

Enhancement of photosensitivity by annealing in Bi2S3 thin films grown using SILAR method

Bi₂S₃ thin films were grown by successive ionic layer adsorption and reaction method (SILAR) onto the glass substrates at room temperature. The as prepared thin film were annealed at 250 °C in air for 30 min. These films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrical measurement systems. The X-ray diffraction patterns reveal that Bi₂S₃ thin film have orthorhombic crystal structure. SEM images showed uniform deposition of the material over the entire glass substrate. The optical energy band gap observed to be decreased from 1.69 to 1.62 eV for as deposited and annealed films respectively. The I–V measurement under dark and illumination condition (100 W) show annealed Bi₂S₃ thin film gives good photoresponse as compared to as deposited thin film and Bi₂S₃ thin film exhibits photoconductivity phenomena suggesting its useful in sensors device. The thermo-emf measurements of Bi₂S₃ thin films revealed n-type electrical conductivity.     

Novel microwave assisted sol–gel synthesis (MW-SGS) and electrochromic performance of petal like h-WO3 thin films

Use of domestic microwave oven is first time employed for chemical deposition of nanocrystalline hexagonal WO₃ (h-WO₃) thin films. Low cost precursors like sodium tungstate, hydrochloric acid, oxalic acid and potassium sulfate signifies cost effectiveness of this thin film fabrication route. Scanning electron microscopy images reveal formation of petal like nanodisks. A number of analytical techniques were used to characterize the WO₃ petal like nanodisks, including X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy, FT-IR spectroscopy, Raman scattering spectroscopy, UV–visible spectrophotometry and cyclic voltammetry (CV). The X-ray photoelectron spectroscopic studies revealed 2.89 O/W atomic ratio. The electrical transport studies on WO₃ thin films show semiconducting behavior with n-type semiconductivity. The value of determined coloration efficiency is 57.90 cm²/C. The mechanism of Li⁺ intercalation and deinercalation in h-WO₃ matrix is proposed for enhanced electrochromism.     

Optimization of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> thin film absorber layer growth without sulphurization using triethanolamine as complexing agent for thin film solar cells applications

Quaternary kesterite Cu₂ZnSnS₄ (CZTS) thin films have been prepared via a simple spin-coating technique based on a sol–gel precursor of 2-methoxyethanol solution with metal salts and thiourea. Solution processed CZTS thin film growth parameters using complexing agent triethanolamine (TEA) have been investigated. Effects of complexing agent TEA on structural, morphological, optical, electrical and photovoltaic properties of CZTS thin films were systematically investigated. X-ray diffraction and Raman spectroscopy studies reveal that amorphous nature of CZTS thin film changes into polycrystalline with kesterite crystal structure with optimized TEA concentartion. Surface morphology of CZTS films were analyzed by field emission scanning electron microscope and atomic force microscope, which revealed the smooth, uniform, homogeneous and densely packed grains and systematic grain growth formation with varying TEA concentrations. UV–Vis spectra revealed a direct energy band gap ranging from 1.78 to 1.50 eV, which was found to depend upon the TEA concentration. X-ray photoelectron spectroscopy demonstrated stoichiometric atomic ratios of multicationic quaternary CZTS thin film grown without sulphurization. p-type conductivity was confirmed using Hall measurements and the effect of varying concentartion of TEA on electrical and photovoltaic properties are studied. The SLG/FTO/ZnO/CZTS/Al thin film solar cell is fabricated with the CZTS absorber layer grown at optimized TAE concentration of 0.06 M. It shows a power conversion efficiency of 0.87% for a 0.16 cm² area with V_oc = 0.257 mV, J_sc = 8.95 mA/cm² and FF?=?38%.     

Enhanced dielectric properties of Mn doped Ba0.6Sr0.4TiO3 thin films fabricated by pulsed laser deposition

Pure and 2 mol% Mn doped Ba_0.6Sr_0.4TiO₃ (BST) thin films have been deposited on La_0.67Sr_0.33MnO₃ (LSMO) coated single-crystal (001) oriented LaAlO₃ substrates using pulsed-laser deposition technique. The bilayer films of BST and LSMO were epitaxially grown in pure single-oriented perovskite phases for both samples, and an enhanced crystallization effect in the BST film was obtained by the addition of Mn, which were confirmed by X-ray diffraction (XRD) and in situ reflective high energy electron diffraction (RHEED) analyses. The dielectric properties of the BST thin films were measured at 100 kHz and 300 K with a parallel-plate capacitor configuration. The results have revealed that an appropriate concentration acceptor doping is very effective to increase dielectric tunability, and to reduce loss tangent and leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 11 (undoped) to 40 (Mn doped) under an applied electric field of 200 kV/cm. The leakage current density of the BST thin films at a negative bias field of 200 kV/cm decreases from 2.5 × 10^− 4 A/cm² to 1.1 × 10^− 6 A/cm² by Mn doping. Furthermore, a scanning-tip microwave near-field microscope has been employed to study the local microwave dielectric properties of the BST thin films at 2.48 GHz. The Mn doped BST film is more homogeneous, demonstrating its more potential applications in tunable microwave devices.     

P-type tin–indium oxide films prepared by thermal oxidation of metallic InSn alloy films

P-type transparent conducting tin–indium oxide (TIO) films were successfully fabricated on quartz substrates by thermal oxidation of InSn alloy (In / Sn = 0.2) films that were deposited by magnetron sputtering at room temperature (R.T.). Structural and electrical properties of TIO films were investigated. X-ray diffraction studies showed that all TIO films were polycrystalline with an orthorhombic structure. The surface morphology of TIO films viewed by field emission scanning electron microscope (SEM) revealed that the films are composed of uniformly distributed submicron grains. Hall effect measurement results indicated that hole concentration as high as 9.61 × 10¹⁸ cm^− 3 was achieved. It's found that 600 °C was the optimum thermal oxidation temperature to get p-type TIO films with highest hole concentration.     

Formation of F-doped ZnO transparent conductive films by sputtering of ZnF2

Fluorine-doped ZnO transparent conductive thin films were successfully deposited on glass substrate by radio frequency magnetron sputtering of ZnF₂. The effects of rapid thermal annealing in vacuum on the optical and electrical properties of fluorine-doped ZnO thin films have been investigated. X-ray diffraction spectra indicate that no fluorine compounds, such as ZnF₂, except ZnO were observed. The specimen annealed at 500 °C has the lowest resistivity of 6.65 × 10^? 4 Ω cm, the highest carrier concentration of 1.95 × 10²¹ cm^? 3, and the highest energy band gap of 3.46 eV. The average transmittance in the visible region of the F-doped ZnO thin films as-deposited and annealed is over 90%.     

Spray pyrolysis deposition of lanthanum telluride thin films and their characterizations

Spray pyrolysis method is used to deposit lanthanum telluride (La₂Te₃) thin films on glass substrates. The films are deposited by pyrolysis of sprayed solutions of LaCl₃ and Te metal dissolved in concentrated HCl and HNO₃ along with hydrazine hydrate as a reducing agent. X-ray diffraction analyses show that the films are polycrystalline with La₂Te₃ phase. The films have a direct optical band gap of 2.2 eV. The films are p-type semiconductors with an electrical resistivity of the order of 10⁴ Ω cm at ambient temperature (27 °C).     

Spray pyrolysed bismuth oxide thin films and their characterization

Uniform, adherent and reproducible bismuth oxide thin films have been deposited on glass substrates from aqueous Bi(NO₃)₃ solution, using the solution spray technique. Their structural, surface morphological, optical, and electrical properties were investigated by XRD, AFM, optical absorption, electrical resistivity and thermo-emf measurements. The structural analysis from XRD pattern showed the formation of mixed phases of monoclinic Bi₂O₃ (predominant), tetragonal β-Bi₂O₃ and nonstiochiometric Bi₂O_2.33. The surface morphological studies on atomic force micrographs revealed round grain morphology of bismuth oxide crystallites. The optical studies showed a direct band gap of 2.90 eV for as-prepared bismuth oxide films. The electrical resistivity measurements of bismuth oxide films indicated a semiconducting behavior with the room temperature electrical resistivity of the order of 10⁷ Ω cm. From thermo-emf measurements, the electrical conductivity was found to be of n-type.     

Thickness and temperature effects on electrical resistivity of (Bi0.5Sb0.5)2Te3 thin films

Thin films of (Bi_0.5Sb_0.5)₂Te₃ of different thickness were deposited on glass substrate by the flash evaporation method in a vacuum of 1 × 10^− 5 Torr. X-ray diffraction and transmission electron microscope analysis indicates that these films are polycrystalline even in the as-deposited state and the post-deposition annealing leads to grain growth. Electrical resistivity studies were carried out on these films as a function of temperature (300– 450 K) and film thickness (450–2000 Å). Temperature dependence of electrical resistivity shows that (Bi_0.5Sb_0.5)₂Te₃ films are semiconducting. It is found that electrical conduction activation energy decreases with increase of film thickness and this observation is explained based on the Slater model. Thickness dependence of electrical resistivity is analyzed using the effective mean free path model of size effect with perfect diffuse scattering. This analysis leads to the evaluation of the important physical parameters i.e., mean free path and bulk resistivity of hypothetical bulk.     

Preparation of Cu2ZnSnS4 thin films by sulfurization of stacked metallic layers

Stacked precursors of Cu, Sn, and Zn were fabricated on glass/Mo substrates by electron beam evaporation. Six kinds of precursors with different stacking sequences were prepared by sequential evaporation of Cu, Sn, and Zn with substrate heating. The precursors were sulfurized at temperatures of 560 °C for 2 h in an atmosphere of N₂ + sulfur vapor to fabricate Cu₂ZnSnS₄ (CZTS) thin films for solar cells. The sulfurized films exhibited X-ray diffraction peaks attributable to CZTS. Solar cells using CZTS thin films prepared from six kinds of precursors were fabricated. As a result, the solar cell using a CZTS thin film produced by sulfurization of the Mo/Zn/Cu/Sn precursor exhibited an open-circuit voltage of 478 mV, a short-circuit current of 9.78 mA/cm², a fill factor of 0.38, and a conversion efficiency of 1.79%.     

Spectroscopic ellipsometry study of thin film thermo-optical properties

Spectroscopic ellipsometry (SE) was employed to realize in-situ monitoring and the determination of thermo-optic coefficients (TOC) of thin films by integrating a temperature controlled hot stage to the ellipsometer and applying the empirical relationship of Cauchy between the refractive index and wavelength in the data analysis. Magnetron sputtered titanium oxide thin films of 350 nm thick both as-deposited and post-deposition annealed were prepared on silicon wafers for this investigation. Results of ellipsometric analysis show that as-deposited TiO₂ films have a negative TOC of ? 1.21 × 10^? 4 K^? 1 at 630 nm over the test temperature range 304–378 K. The post-deposition annealing at 923 K for 2 hours leads an increase in film refractive index to 2.29 from 2.17 for as-deposited TiO₂ films, and an enhancement in TOC up to ? 2.14 × 10^? 4 K^? 1. X-ray diffraction (XRD) and scanning electron microscopy (SEM) cross-sectional analysis were performed for film structure characterization.     

Influence of Ar/O2 ratio on the properties of transparent conductive ZnO:Ga films prepared by DC reactive magnetron sputtering

Ga-doped zinc oxide (ZnO:Ga) transparent conductive films with highly (002)-preferred orientation were deposited on glass substrates by DC reactive magnetron sputtering method in Ar + O₂ ambience with different Ar/O₂ ratios. The structural, electrical, and optical properties were investigated by X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The resistivity and optical transmittance of the ZnO:Ga thin films are of the order of 10^− 4 Ω cm and over 85%, respectively. The lowest electrical resistivity of the film is found to be about 3.58 × 10^− 4 Ω cm. The influences of Ar/O₂ gas ratios on the resistivity, Hall mobility, and carrier concentration were analyzed.     

Nanocrystalline sol–gel TiO2–SnO2 coatings: Preparation,characterization and photo-catalytic performance

In this study, preparation of SnO₂ (0–30 mol% SnO₂)–TiO₂ dip-coated thin films on glazed porcelain substrates via sol–gel process has been investigated. The effects of SnO₂ on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Surface topography and surface chemical state of thin films were examined by atomic force microscopy and X-ray photoelectron spectroscopy. XRD patterns showed an increase in peak intensities of the rutile crystalline phase by increasing the SnO₂ content. The prepared Sn doped TiO₂ photo-catalyst films showed optical absorption in the visible light area exhibited excellent photo-catalytic ability for the degradation of methylene blue under visible light irradiation. Best photo-catalytic activity of Sn doped TiO₂ thin films was measured in the TiO₂–15 mol% SnO₂ sample by the Sn⁴⁺ dopants presented substitution Ti⁴⁺ into the lattice of TiO₂ increasing the surface oxygen vacancies and the surface hydroxyl groups.     

Sulfurization free spray deposited kesterite Cu2ZnSnS4 absorber layer for photovoltaic applications

The growth of Cu₂ZnSnS₄ thin films was optimized via sulfurization free chemical spray pyrolysis technique. The sulfate based precursors were used to prepare the CZTS films with varying sulfur contents ranging from 0.08 to 0.12 M to maintain the stoichiometric and avoid sulfurization or H₂S gas. The formation of secondary phases on the CZTS films was minimized by controlling the sulfur concentrations with the 2- methoxyethanol solvent. The CZTS kesterite structure with preferential orientation along (112) plane was confirmed by X-Ray diffraction at the sulfur content of 0.12 M. From the Raman analysis, we observed that the addition of the higher sulfur concentration to the precursor solution resulted in a pure phase CZTS peak at 336 cm^?1 and reduces the secondary phase segregation. Scanning electron microscopy confirms that higher sulfur concentrations facilitate the growth of CZTS films with larger grain size and achieved Cu-poor and Zn-rich compositions for 0.12 M sulfur concentration from energy dispersive spectra. The UV analysis revealed the maximum absorption peak in the visible region with increasing sulfur concentration and the measurement of the Hall effect affirmed p-type conductivity with carrier concentrations ranging from 10¹⁴ to 10¹⁶ cm^?3 as sulfur concentration increased. The charge transport property of the deposited films was characterized by electrochemical impedance spectroscopy where higher sulfur concentrations resulted in lower internal charge transfer resistance, which is the ideal absorber layer in thin film photovoltaic cells.

     

Influence of Nd dopant amount on microstructure and photoluminescence of TiO2:Nd thin films

TiO₂ and TiO₂:Nd thin films were deposited using reactive magnetron sputtering process from mosaic Ti–Nd targets with various Nd concentration. The thin films were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and spectroscopic techniques. Photoluminescence (PL) in the near infrared obtained upon 514.5 nm excitation was also examined. The relationship between the Nd concentration, structural, optical and photoluminescence properties of prepared thin films was investigated and discussed. XRD and TEM measurements showed that an increase in the Nd concentration in the thin films hinders the crystal growth in the deposited coatings. Depending on the Nd amount in the thin films, TiO₂ with the rutile, mixed rutile–amorphous or amorphous phase was obtained. Transmittance measurements revealed that addition of Nd dopant to titania matrix did not deteriorate optical transparency of the coatings, however it influenced on the position of the fundamental absorption edge and therefore on the width of optical band gap energy. All TiO₂:Nd thin films exhibited PL emission that occurred at ca. 0.91, 1.09 and 1.38 μm. Finally, results obtained for deposited coatings showed that titania with the rutile structure and 1.0 at.% of Nd was the most efficient in VIS to NIR photon conversion.     

Cu2ZnSnS4 films by paste coating and their optoelectronic properties

Cu₂ZnSnS₄ (CZTS) thin films were prepared by a paste coating method as the absorb layer of solar cells. This method is more eco-friendly using ethanol as solvent and more convenient than traditional sol–gel method. The effects of sulfurization temperature on properties of thin film were studied. The results of X-ray diffraction and Raman spectroscopy showed the formation of kesterite structure of CZTS films. The scanning electron microscopy images revealed that CZTS thin film obtained at 550 °C were compact and uniform. The optical band gap of the CZTS film was about 1.5 eV, and the CZTS film had an obvious optoelectronic response. Moreover, CZTS solar cell was prepared with a conversion efficiency of 0.47 %.     

Preparation of ZnO:Al thin film on transparent TPT substrate at room temperature by RF magnetron sputtering technique

Aluminum doped ZnO thin films (ZnO:Al) deposited on flexible substrates are suitable to be used as transparent conductive oxide (TCO) thin films in solar cells because of the excellent optical and electrical properties. TPT films are a kind of composite materials and are usually used as encapsulation material of solar panels. In this paper, ZnO:Al film was firstly deposited on transparent TPT substrate by RF magnetron sputtering. The structural, optical, and electrical properties of the film were investigated by X-ray diffractometry (XRD), scanning electron microscope (SEM), UV–visible spectrophotometer, as well as Hall Effect Measurement System. Results revealed that the obtained film had a hexagonal structure and a highly preferred orientation with the c-axis perpendicular to the substrate. Also, the film showed a high optical transmittance over 80% in the visible region and a resistivity of about 3.03 × 10^? 1 Ω·cm.     

Investigation of structural,optical and micro-mechanical properties of (NdyTi1 − y)Ox thin films deposited by magnetron sputtering

TiO₂ and (Nd_yTi_1 − y)O_x thin films were deposited by reactive magnetron sputtering process from mosaic Ti–Nd targets and characterised by X-ray diffraction (XRD), Raman optical spectroscopy and nanoindentation technique. XRD measurements revealed that as-prepared titanium dioxide and TiO₂ thin films with 4 and 7 at.% of Nd had nanocrystalline rutile structure, while coatings with larger amount of Nd were amorphous. Raman spectroscopy investigations showed that the increase of the neodymium concentration caused amorphisation of the coatings and hindered their crystal growth. All as-prepared coatings were transparent in the visible wavelength range with a transmittance of approximately 80%. The refractive index and extinction coefficient of the thin films gradually decreased with the increase of the neodymium concentration. Micro-mechanical properties, i.e. hardness and elastic modulus, were determined using traditional load-controlled nanoindentation testing and continuous stiffness measurements. The highest hardness and elastic modulus values were obtained for thin films with 7 at.% of Nd and were approximately 14.8 GPa and 166.3 GPa, respectively.