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In this paper, we employed a quadruple-layer antireflection coating structure with Al2O3 deposited by DC reactive magnetron sputtering and SiO2 deposited by PECVD (plasma enhanced chemical vapor) deposition as the bottom layer, and proposed an optical optimization program for quadruple-layer antireflection coatings to obtain the structure parameters. In the experiment, two types of optimization quadruple-layer antireflection coatings and typical SiNx:H double-layer antireflection coatings were deposited on the crystalline silicon solar cells. The reflectance of the silicon solar cell with quadruple-layer antireflection coatings was lower than that of the solar cell with SiNx:H double-layer antireflection coatings. These results demonstrated the possibility of substituting quadruple-layer antireflection coatings for double-layer antireflection coatings, as well as the feasibility of the application in photovoltaic.

Here we show that when the temperature exceeded 1200 &deg, C, the tensile strength drops sharply with change of fracture mode from fiber pull-out to fiber-break. Theoretical analysis indicates that the reduction of tensile strength and change of fracture mode is due to the variation of residual radial stress on the fiber&ndash, matrix interface coating. When the temperature exceeds the preparation temperature of the composites, the residual radial stress on the fiber&ndash, matrix interface coating changes from tensile to compressive, leading to the increase of the interface strength with increasing temperature. The fracture behavior of SiC&ndash, SiC composites changes from ductile to brittle when the strength of fiber&ndash, matrix interface coating exceeds the critical value. Theoretical analysis predicts that the high temperature tensile strength can increase with a decrease in fiber&ndash, matrix interface thickness, which is verified by experiments.

Here, we show that when the oxidation treatment temperature exceeded 600°C, the tensile strength of SiC/SiC begins to decrease. Oxidation leads to the damages on the PyC fiber/matrix interface, which is replaced by SiO2 at higher temperature. The fracture mode converts from fiber pull-out to fiber-break as the fiber/matrix interface is filled with SiO2. Oxidation time also plays an important role in affecting the tensile strength of SiC/SiC. The tensile modulus decreases with temperature from RT to 800°C, then increases above 800°C due to the decomposition of remaining CSi x O y and crystallization of the SiC matrix. A special surface densification treatment performed in this study is confirmed to be an effective approach to reduce the oxidation damages and improve the tensile strength of SiC/SiC after oxidation.

Continuous silicon carbide fiber-reinforced silicon carbide ceramic matrix composites (SiCf/SiC) are promising as thermal structural materials. In this work, the microstructure and static mechanical properties of 3D-SiCf/SiC with PyC, SiC, and PyC/SiC and without an interface prepared via polymer infiltration and pyrolysis (PIP) were investigated systematically in this paper. The results show that the microstructure and static mechanical properties of SiCf/SiC with an interphase layer were superior to the composites without an interlayer, and the interface debondings are existing in the composite without an interphase, resulting in a weak interface bonding. When the interphase is introduced, the interfacial shear strength is improved, the crack can be deflected, and the fracture energy can be absorbed. Meanwhile, the shear strength of the composites with PyC and PyC/SiC interfaces was 118 MPa and 124 MPa, respectively, and showing little difference in bending properties. This indicates that the sublayer SiC of the PyC/SiC multilayer interface limits the binding state and the plastic deformation of PyC interphase, and it is helpful to improve the mechanical properties of SiCf/SiC.

In this paper, the two-step sequential deposition method was used to prepare the CH3NH3PbBrXI3-X films by introducing CH3NH3Br in the precursors. The surface morphology of the PbI2 films was controlled by anti-solvent extraction (ASE) to improve the microstructure and photo-physical properties of the perovskite films. It was noteworthy that, compared to the compact PbI2 films, the porous PbI2 films facilitated the growth of crystals and bromine incorporation in films, and the prepared perovskite films exhibited enlarged grain size, increased light absorption, enhanced Br incorporation and prolonged carrier lifetime, which resulted in excellent photo-electrical properties of the CH3NH3PbBrXI3-X films. With porous PbI2 templates, the inverted planar perovskite solar cells based on films with appropriate Br incorporation (CH3NH3Br/CH3NH3I mole ratio = 3/7) showed a photovoltaic conversion efficiency (PCE) of 14.9%, and the stability of the devices in air was elevated. Consequently, the high-quality CH3NH3PbBrXI3-X films can be obtained with porous PbI2 templates for improving the performance of the perovskite solar cells.

In this study, pentabasic CuInxGayAl1-x-ySe2 (CIGAS) powder was prepared by heating in ethylene diamine at 290 °C for 20 h, using a solvent thermal reaction technique. The microstructures and electrical properties of the CIGAS targets doped with different aluminum content were investigated by XRD, SEM, XPS and Hall Effect techniques. The results indicate that Al doping had an important effect on the electrical properties and microstructure of the CIGAS targets, especially at the (112) crystal orientation. It was found that the peak of (112) clearly shifted to higher 2θ values with the increase of aluminum incorporation, while the peak intensity weakened gradually, thus indicating that the crystallinity of the CIGAS targets decreased. The SEM results revealed that the sizes of the CIGAS grains could be adjusted by varying the stoichiometric ratio of In, Ga and Al, and that the Al incorporation could enhance the density of the CIGAS targets. The XRD and XPS analysis showed that some In and Ga atoms in the crystal lattice of chalcopyrite structure could be replaced with Al atoms in the CIGAS materials. Finally, the electrical properties of the targets were analyzed based on the Hall Effect measurements. The results showed that the conductivity, mobility and carrier concentration of the targets changed significantly along with the increase of the Al incorporation content, and that the mobility reducing may have been a result of Al incorporation, which prevents the grain from growing, followed by high-density target forming.

In this paper, a new fabrication method for silicon nanowires/micropillars structure is proposed. This method is using lithography and metal-assisted chemical etching to fabricate the structure of silicon nanowires/micropillars. In the experiment, to obtain the optimal light trapping properties of silicon nanowires/micropillars structure, the optimal light trapping properties of silicon nanowires were systemically investigated, including etching concentration, etching time and etching temperature. And then, a large-area uniform, controllable and optimal light trapping silicon nanowires/micropillars structure was fabricated using lithography and metal-assisted chemical etching method. This controllable and facile method for silicon nanowires/micropillars structure will expand its application in the field of optoelectronic devices and solar cells.

In this paper, the CH3NH3PbI3−xBrx films with various Br-doping contents were successfully prepared by solution processed deposition and followed by annealing process. This method simultaneously modified the morphology and composition of the CH3NH3PbI3 film. The effects of annealing treatment of CH3NH3PbI3−xBrx films under N2 and DMSO conditions on the microstructure of films and photoelectric properties of the solar cells were systematically investigated. The relationship of the component ratio of RBr/I= CH3NH3PbI3−xBrx/CH3NH3PbI3 in the resulting perovskite versus CH3NH3Br concentration also was explored. The results revealed that the CH3NH3PbI3−xBrx films annealed under DMSO exhibited increased grain sizes, enhanced crystallinity, enlarged bandgap and reduced defect density compared with that of the N2 annealing. It also was found that the RBr/I linearly increased in the resulting perovskite with the increased of CH3NH3Br concentration in the methylammonium halide mixture solutions. Furthermore, the photovoltaic performances of devices fabricated using DMSO precursor solvent were worse than that of DMF under N2 annealing atmosphere. When CH3NH3Br concentration was 7.5 mg ml−1, the planar perovskite solar cell based on CH3NH3PbI3−xBrx annealed under DMSO showed the best efficiency of 13.7%.

In this work, the fabrication of boron-doped nanocrystalline silicon (nc-Si) deposited on PET substrate at room temperature are reported. Negative substrate bias is applied during deposition for improving the crystallinity of samples. The effects of negative bias on the structural, electrical and optical properties of B-doped nc-Si thin films prepared on PET are systemically studied through various characterizations. XRD and Raman results show that a phase transition from amorphous phase to crystalline phase takes place at negative bias = 80 V. By using moderate negative bias, the crystalline volume fraction can be effectively improved. The electrical properties have been found related to the crystalline volume fraction. At negative bias = 120 V, the maximum values of dark conductivity (1.94 S/cm) and carrier concentration (7.4 × 1019 cm− 3) are obtained for the sample which has the largest crystalline volume fraction. Furthermore, the promotion mechanism on B-doping was illustrated in this paper.

It is widely known that solvent engineering has a significant effect on the growth of high quality perovskite film. However, the crystal evolution process and crystal compositions of perovskite film when applying the two-step method are multifaceted, and the effects on the photoelectrical properties for the perovskite layer still require further study. In this study, the above two issues are systematically studied. Combining the XRD and photoluminescence spectra results, it was observed that the residual PbI2 decreased with the increase of DMSO in DMSO/DMF solvents and that there were two types of local phase crystallites (disordered and ordered) in the perovskite films. The phase transitions of the crystals were investigated with the ratio of DMSO increasing in the mixed solvents. In addition, the interfacial defect states in the PbI2/perovskite interface which can act as charge carrier trapping centers were significantly affected by the photo(dark) conductivity of the perovskite film. It was also observ...

In this study, the phosphorus doped silicon nanocrystals embedded in silicon-rich SiNx:H thin films were fabricated using a radio frequency plasma enhanced chemical vapor deposition technique, from a SiH4, pH3, H2 and NH3 mixture. The effects of nitrogen incorporation on the microstructure and photoelectric properties of the nc-Si:H film were systematically investigated. Raman and transmission electron microscope observation revealed the fact that nitrogen incorporation inhibited the growth of Si nanocrystals, and their sizes and densities of them could be adjusted by varying the incorporation flow ratio NH3/(SiH4 + H2 + pH3). The reduction of refractive index and improvement of conductivity of the prepared films were observed with increasing nitrogen impurity, and a maximal conductivity was obtained when the flow ratio was 0.02. In addition, the P-doped nc-SiNx:H film was used as an n-type layer for the amorphous silicon thin film solar cells to optimize its efficiency, and the solar cell with high fill factor (0.624) and efficiency (9.26%) has been obtained when the flow ratio was 0.02. As a result, the P-doped nc-SiNx:H film with proper nitrogen incorporation was able to efficiently improve the performance of the thin film solar cells.

In this study, a SiOx:H/bi-SiNx:H/SiOx:H quadruple-layer anti-reflective coatings embedded by silicon nanocrystals (Si-NC ARCs) was deposited on an n-type monocrystalline silicon base solar cell with nanowire texturing, by means of plasma enhancing chemical vapor deposition. The average reflection of the Si-NC ARCs on the polished silicon wafer was 4.97% (300–1000 nm). The minority carrier lifetime of the silicon wafer with nanowire texturing was boosted by nearly 39 times after the Si-NC ARCs were deposited. Moreover, the Si-NC ARCs showed a significant luminescent down shifting effect (LDS), with strong absorbing at the blue-ultraviolet region, followed by re-emitting at the red-near-infrared region, thereby modifying the sunlight spectrum before they reached the solar cell, and thus obtaining a better spectrum response. After depositing the Si-NC ARCs without a significant increase in the cell cost, the external quantum efficiencies, short circuit current density and photo-conversion efficiency of the solar cell with nanowire texturing were significantly improved.

Phosphorus doped Si nanocrystals (SNCs) emebedded in silicon-rich SiNx:H films were prepared using plasma enhanced chemical vapor deposition technique, and the effects of nitrogen incorporation on the microstructure and electronic properties of the thin films have been systematically studied. Transmission electron microscope and Raman observation revealed that nitrogen incorporation prevents the growth of Si nanocrystals, and that their sizes can be adjusted by varying the flow rate of NH3. The reduction of photoluminescence (PL) intensity in the range of 2.1–2.6 eV of photon energy was observed with increasing nitrogen impurity, and a maximal PL intensity in the range 1.6–2.0 eV was obtained when the incorporation flow ratio NH3/(SiH4+H2+PH3) was 0.02. The conductivity of the films is improved by means of proper nitrogen impurity doping, and proper doping causes the interface charge density of the heterojunction (H-J) device to be lower than the nc-Si:H/c-Si H-J device. As a result, the proper incorporation of nitrogen could not only reduce the silicon banding bond density, but also fill some carrier capture centers, and suppress the nonradiative recombination of electrons.

Drilling is important for back contact solar cells, which form a good ohmic contact between a front surface and a rear surface. However, drilling causes increases of breakages and cracks in a back contact solar cell when the silicon wafer is thinner and larger than that of conventional cells. In the present paper, the node value method of finite element post-processing, including a stress concentration factor, a Von Mises stress and a sub-model, is used to achieve a quantitative analysis involving the stress concentration of a silicon wafer with multiple holes under thin film residual stress. The results show that drilling which changes the stress field distribution in a silicon wafer generates a stress concentration around the holes. This stress concentration can be reduced by increasing the thickness of a silicon wafer, decreasing the drilling ratio and replacing the morphologies of trapezoidal holes with those of cylindrical holes. The results of the simulation are in accordance with the experimental results adopted by Raman spectra and three-point bending tests. Our results provide a beneficial reference for decreasing stress concentration in back contact solar cells. Display Omitted The stress distributions in silicon wafers with multiple holes are analyzed.A Raman spectrum and three-point bending test are used for characterization the stress distributions.The influence of drillings ratio, hole morphology and wafer thickness on the stress distributions is discussed.

Using fibre web/copper mesh integrated fabric as the preform, carbon fibre and copper fibre fabric reinforced carbon matrix (Cf/Cu/C) composites with different types of carbon matrix were prepared by chemical vapor infiltration (CVI) technique with C3H6 + N2 and impregnation/carbonization (I/C) technique with furan resin. The microstructures, mechanical and tribological properties of Cf/Cu/C composites with resin carbon, pyrolytic carbon (PyC) and PyC/resin carbon matrix were characterized. The results show that Cf/Cu/C composites with PyC matrix possess the highest flexural strength and the lowest hardness. Cf/Cu/C composites with resin carbon matrix have the highest wear rate and friction coefficient, and the failure mechanism includes both abrasive wear and delamination wear. For Cf/Cu/C composites with PyC matrix, the wear process is mainly controlled by abrasive wear. It is easier for PyC matrix to form a lubricant film.

A carbon/carbon–Al–Cu composite reinforced with carbon fiber 2.5D-polyacrylonitrile-based preforms was fabricated using the pressureless infiltration technique. The Al–Cu alloy liquids were successfully infiltrated into the C/C composites at high temperature and under vacuum. The mechanical and metallographic properties, scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS) of the C/C–Al–Cu composites were analyzed. The results showed that the bending property of the C/C–Al–Cu composites was 189 MPa, whereas that of the pure carbon slide material was only 85 MPa. The compressive strength of C/C–Al–Cu was 213 MPa, whereas that of the pure carbon slide material was only 102 MPa. The resistivity of C/C–Al–Cu was only 1.94 μΩm, which was lower than that of the pure carbon slide material (29.5 μΩm). This finding can be attributed to the “network conduction” structure. Excellent wettability was observed between Al and the carbon matrix at high temperature due to the existence of Al4C3. The friction coefficients of the C/C, C/C–Al–Cu, and pure carbon slide composites were 0.152, 0.175, and 0.121, respectively. The wear rate of the C/C–Al–Cu composites reached a minimum value of 2.56 × 10−7 mm3/Nm. The C/C–Al–Cu composite can be appropriately used as railway current collectors for locomotives.

The fine-grained target categories/types are very critical for improving the performance of entity search because they can be used for retrieving relevant entities by filtering irrelevant entities with a high confidence. However, most solutions of entity search face an urgent problem, i.e., the lack of fine-grained target categories of queries, which are hard for users to explicitly specify. In this paper, we try to interpret fine-grained categories from natural language based queries of entity search. We observe that entity search queries often contain terms specifying the contexts of the desired entities, as well as a topic of the desired entities. Accordingly, we propose to interpret fine-grained categories of entity search queries from the context perspective and the topic perspective. Therefore, we propose an approach by formalizing both context-based category model and topic-based category model, to tackle the category interpreting task. Extensive experiments on two widely-used test sets: INEX-XER 2009 and SemSearch-LS, indicate significant performance improvement achieved by our proposed method over the state-of-the-art baselines.

Ad-hoc entity search, which is to retrieve a ranked list of relevant entities in response to a query of natural language question, has been widely studied. It has been shown that category matching of entities, especially when matching to fine-grained entity types/categories, is critical to the performance of entity search. However, the potentials of the fine-grained Wikipedia entity categories, has not been well exploited by existing studies. Based on the observation of how people describe entities of a specific type, we propose a headword-and-modifier model to deeply interpret both queries and fine-grained entity types/categories. Probabilistic generative models are designed to effectively estimate the relevance of headwords and modifiers as a pattern-based matching problem, taking the Wikipedia type taxonomy as an important input to address the ad-hoc representations of concepts/entities in queries. Extensive experimental results on three widely-used test sets: INEX-XER 2009, SemSearch-LS and TREC-Entity, show that our method achieves a significant improvement of the entity search performance over the state-of-the-art methods.

The paper introduces an open domain entity search system called ESearch, which aims at finding a list of relevant entities to an open domain entity search query (a natural language question). The system is built on top of a Wikipedia text corpus, as well as the structured DBPedia knowledge base. Entities are initially ranked by a model which effectively associates context matching (based on the contexts of entities in the unstructured text corpus) and category matching (based on the types of entities in the structured knowledge base). They are ranked further by a re-ranking component supported by blind feedback or user feedback on entities. We show that category matching is critical for the search performance and the re-ranking component can boost the performance largely. Category matching therefore needs some query entity types (especially specific entity types) as input. However, it is often hard for systems to detect specific entity types because users may not be familiar with how the types of desired entities are defined in the structured knowledge base. In ESearch, we design an effective ranking model of entity types to facilitate blind feedback and user feedback on desired entity types for category matching, so that users can effectively perform entity search without the need of explicitly providing any query entity types as inputs.

High performance silicon combined structure (micropillar with Cu nanoparticles) solar cell has been synthesized from N-type silicon substrates based on the micropillar array. The combined structure solar cell exhibited higher short circuit current rather than the silicon miropillar solar cell, which the parameters of micropillar array are the same. Due to the Cu nanoparticles were decorated on the surface of silicon micropillar array, the photovoltaic properties of cells have been improved. In addition, the optimal efficiency of 11.5% was measured for the combined structure solar cell, which is better than the silicon micropillar cell.High performance silicon combined structure (micropillar with Cu nanoparticles) solar cell has been synthesized from N-type silicon substrates based on the micropillar array. The combined structure solar cell exhibited higher short circuit current rather than the silicon miropillar solar cell, which the parameters of micropillar array are the same. Due to the Cu nanoparticles were decorated on the surface of silicon micropillar array, the photovoltaic properties of cells have been improved. In addition, the optimal efficiency of 11.5% was measured for the combined structure solar cell, which is better than the silicon micropillar cell.

In this paper, a method to obtain the CuInGaSe2 (CIGS) absorber layer with an appropriate selenium content is put forward, in which a Se-rich target is used to deposit a CIGS thin-film and this film is annealed in a Se-free inert atmosphere. The key issue of this method is the preparation of a Se-rich target with a homogeneous composition and a high-density. The formation mechanism of CuInSe2 and CuGaSe2 is investigated and the results point to the intermediate phase Cu2−xSe playing a role of a nucleation core. The sintering densification trajectory of the target with the addition of extra selenium is researched. Additionally, an effective way to avoid the sintering defects is proposed. Finally, a conversion efficiency of 11.2% for the CIGS solar cell is reached by sputtering from the obtained Se-rich target.

Preference queries serve for retrieving a small set of tuples with top aggregated scores over multiple features, from a large set of tuples. We consider the problem of maintaining the ranking lists of items for preference queries in dynamic virtual environments, which is very useful for avatars in virtual environments to continuously monitor interesting items surrounding them. Traditional solutions on preference queries utilize the pre-computed materialized ranking lists to efficiently find top items by only retrieving a prefix of the ranking lists. However, for preference queries in virtual environments, items (tuples) to be ranked change frequently due to the movements and updates of avatars. Creating and maintaining materialized ranking lists in such dynamic scenarios will be extremely expensive. In this paper, we address the problem by proposing a solution as a marriage of continuous range query and continuous top-k query. A preference query is continuously processed by dynamically adding and removing the perceived items of an avatar. Extensive experimental studies show that the proposed techniques are very efficient in handling the continuous updates of ranking lists.

CuInxGayAl1-x-ySe2 powders were prepared using a solvothermal reaction technique in ethylenediamine at 290°C for 20 hours. The microstructure and optical absorption properties of the powders were investigated by XRD, SEM, TEM, XPS and UV-Vis-NIR spectra. The results indicated that the Al atom was successfully incorporated into the CuInxGa1-xSe2 lattices, and Al doping had a significant effect on the microstructure, especially at the (112) crystal orientation. It was found that the peak of (112) shifted obviously to higher 2θ values with the increasing aluminum content. Transmission electron microscope observation revealed that the size of the CuInxGayAl1-x-ySe2 nanoparticles could be adjusted by varying the stoichiometric ratio of the In, Ga and Al, and the proper Al incorporation could reduce the density of the stacking faults and nanotwins in the CuInxGayAl1-x-ySe2 materials. XRD analysis indicated that the Al incorporation could effectively substitute In and Ga atoms. Finally, the band gap was obtained by UV-Vis-NIR spectra, and the results implied that the optical absorption value decreased and optical band gap increased significantly with the incorporation of Al, and it is close to the optimal band gap (1.37 eV) of solar cells when the stoichiometric ratio of the Al was between 0.2 and 0.3.