ABSTRACT
The perovskite solar cells (PSCs) are still facing the two main challenges of stability and scalability to meet the requirements for their potential commercialization. Therefore, developing a uniform, efficient, high quality and cost-effective electron transport layer (ETL) thin film to achieve a stable PSC is one of the key factors to address these main issues. Magnetron sputtering deposition has been widely used for its high quality thin film deposition as well as its ability to deposit films uniformly on large area at the industrial scale. In this work, we report on the composition, structural, chemical state, and electronic properties of moderate temperature radio frequency (RF) sputtered SnO2. Ar and O2 are employed as plasma-sputtering and reactive gases, respectively. We demonstrate the possibility to grow a high quality and stable SnO2 thin films with high transport properties by reactive RF magnetron sputtering. Our findings show that PSC devices based on the sputtered SnO2 ETL have reached a power conversion efficiency up to 17.10% and an average operational lifetime over 200 h. These uniform sputtered SnO2 thin films with improved characteristics are promising for large photovoltaic modules and advanced optoelectronic devices.
ABSTRACT
In the present work, we report on the microstructural and optoelectronic properties of SnOx thin films deposited by a reactive radio frequency magnetron sputtering. After SnOx growth by sputtering under O2/Ar flow, we have used three different treatment methods, namely (1) as deposited films under O2/Ar, (2) vacuum annealed films ex-situ, and (3) air annealed films ex-situ. Effects of the O2/Ar ratios and the growth temperature were investigated for each treatment method. We have thoroughly investigated the structural, optical, electrical and morphology of the different films by several advanced techniques. The best compromise between electrical conductivity and optical transmission for the use of these SnOx films as an n-type TCO was the conditions O2/Ar = 1.5% during the growth process, at 250 °C, followed by a vacuum post thermal annealing performed at 5 × 10-4 Torr. Our results pointed out clear correlations between the growth conditions, the microstructural and optoelectronic properties, where highly electrically conductive films were found to be associated to larger grains size microstructure. Effects of O2/Ar flow and the thermal annealing process were also analysed and discussed thoroughly.
ABSTRACT
An approximate solution for n-point correlation functions is developed in this study. In the approximate solution, weight functions are used to connect subsets of (n-1)-point correlation functions to estimate the full set of n-point correlation functions. In previous related studies, simple weight functions were introduced for the approximation of three and four-point correlation functions. In this work, the general framework of the weight functions is extended and derived to achieve optimum accuracy for approximate n-point correlation functions. Such approximation can be utilized to construct global n-point correlation functions for a system when there exist limited information about these functions in a subset of space. To verify its accuracy, the new formulation is used to approximate numerically three-point correlation functions from the set of two-point functions directly evaluated from a virtually generated isotropic heterogeneous microstructure representing a particulate composite system. Similarly, three-point functions are approximated for an anisotropic glass fiber/epoxy composite system and compared to their corresponding reference values calculated from an experimental dataset acquired by computational tomography. Results from both virtual and experimental studies confirm the accuracy of the new approximation. The new formulation can be utilized to attain a more accurate approximation to global n-point correlation functions for heterogeneous material systems with a hierarchy of length scales.
ABSTRACT
The tensile yield stress of plasticized starch filled with montmorillonite has been studied as a function of the temperature and the strain rate and has been compared to the yield behavior of the original matrix. Aggregated/intercalated and exfoliated nano-biocomposites, obtained from different nanofillers, have been produced and tested under uniaxial tension (tensile test). To model the nanocomposite tensile yield stress behavior, a preexisting micro-mechanically based cooperative model, which describes properly the yield of semi-crystalline polymers has been modified. According to our development, the yield behavior of nano-biocomposites is strongly dependant on the clay concentration and exfoliation ratio. Based on the thermodynamics properties, an effective activation volume and effective activation energy are computed through the Takayanagi homogenization model. The predicted results for the yield stress at low strain rates and at different temperatures are in agreement with our experimental results.
ABSTRACT
The elastic modulus and yield stress behaviour of a melt intercalated Poly(methylmethacrylate)/ organoclay (PMMA/C30B and PMMA/C20A) were studied using uniaxial tensile tests at different temperatures and different strain rate. The stress-strain response was obtained for different loading rates and different test temperature. Both the stiffness and the yield stress were then clearly identified as function of strain rate and temperature. Our experimental results show that the yield stress and modulus of both PMMA/C20A and PMMA/C30B organoclay nanocomposites are very sensitive to clay concentration, strain rate and temperature. A micromechanically-based composite approach was used to predict the yield stress of both PMMA/C20A and PMMA/C30B organoclay nanocomposites. The results obtained from the model are in good agreement with our experimental results. As expected, the activation enthalpy of cooperative model increased slightly while the activation volume decreases slightly with the clay concentration.
ABSTRACT
In this paper, we report the use of the TMCVD technique for the optimisation of deposited diamond films onto Ti6Al4V substrates. A number of samples were made varying the experimental parameters. The specimen surfaces were characterised using micro Raman spectra and SEM analyses. Results show that very different surface finish (from micro to nanostructures) and film characteristics can be obtained from the experimental parameters used. The quality of deposited diamond is very dependant on the experimental settings and process. It was found that lower residual stresses are developed using the TMCVD technique than with conventional CVD but depend on the structural diamond growth during the process. The quality of the deposited film was evaluated as a function of diamond to amorphous carbon ratio but showed no direct relation with the surface finish since it characterises the quality of the deposited diamond but not the quality of the film surface.
Subject(s)
Coated Materials, Biocompatible/chemistry , Crystallization/methods , Diamond/chemistry , Membranes, Artificial , Nanostructures/chemistry , Nanostructures/ultrastructure , Titanium/chemistry , Adsorption , Alloys , Gases/chemistry , Macromolecular Substances/chemistry , Materials Testing , Molecular Conformation , Nanotechnology/methods , Particle Size , Surface PropertiesABSTRACT
The present work is concerned with the improvement of thermal properties and mechanical strength of adhesive joints consisting of an epoxy adhesive layer bonding aluminium substrates by grafted nanosilica. Epoxy resin/silica nanocomposites were prepared by using functionalized silica. Silica was functionalized by amine group (SiO2-NH2). It was identified by Raman and Fourier Transform Infrared (FTIR). Effects of silica on viscoelastic properties for epoxy resin and its assemblies with aluminium substrates were studied by Dynamical Mechanical Analysis (DMA). Particles distribution was characterized by Scanning Electron Microscope (SEM). Our experimental results showed that functionalized silica presents a better distribution in the matrix than the pure silica. Our results also showed that grafting of functionalized silica improves the glass transition temperature (Tg) and the ultimate strength of aluminium/epoxy/aluminium assembly.
ABSTRACT
Poly(methyl methacrylate) (PMMA) based nanocomposites were synthesized by melt intercalation technique using organoclays (Cloisite 30B and Cloisite 20A) as fillers. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to determine the dispersion and the morphology of the nanocomposites obtained. Thermomechanical tests including tensile test and dynamic mechanical analysis (DMA) were used to evaluate the Young's modulus, storage modulus and the glass transition temperature. Thermogravimetric analysis (TGA) is conducted on the poly(methyl methacrylate) based nanocomposites to determine their thermal stability. The effect of filler content is studied by considering samples with filler contents varying from 1 to 5 wt%. The mechanical properties obtained from the tensile tests show an increase in the Young's modulus and a decrease in the strain to failure as function of the nanoclays concentration. Relative to the pure poly(methyl methacrylate), the dynamic mechanical analyses show an increase in the storage modulus and the glass transition temperature of both nanocomposites. The thermogravimetric analysis shows an increase of the thermal stability of both nanocomposites.
ABSTRACT
In this work carbon nanotubes (CNTs) were used to increase the strength and toughness of the hydroxyapatite (HA) and consequently to reduce its brittleness. The combination of CNT, HA and polymethyl methacrylate (PMMA) has led to a new composite material, which has mechanical properties superior to those of conventional HA/PMMA for biomedical scaffold in tissue engineering. PMMA is a well known bone cement which is highly compatible with HA and also it can act as a functionalizing/linking material with HA. The mechanical properties of the new nanocomposite were predicted with a self-consistent computational model taking into account the structure morphology and the orientation of the CNTs. CNT reinforced HA composite is shown to be a promising coating material for high-load-bearing metal implants. The development of this new nanocomposite based on HA/PMMA and CNTs, may significantly contribute to the bond strength of the HA/PMMA metal interface and the overall mechanical properties of the HA/PMMA coating.
