Fabrication of polycrystalline silicon solar cells showing high efficiency

The paper presents a methodology for fabrication of low-costing silicon solar cells with an efficiency of 10%. A polycrystalline silicon wafer, size 100×100 mm and thickness 450 μm, was doped with phosphorus using POCl₃ as the dopant. While, the backside (p-side) of the wafer was printed with a paste of Ag+Al in the ratio of 25 : 1, the front side (n-side) was printed with a paste of silver. It was fired at 720°C for better ohmic contact. Chemical vapour deposition (CVD) method was adopted for antireflection coating. Pure oxygen gas was bubbled through a solution of TiCl₄ at 200°C. The fabricated cells gave a significant increase in efficiency in terms of open circuit voltage (V) 560 mV, short circuit current (I) of 2·7 amp, and fill factor of 0·73. The methods used are inexpensive, and suitable for production of efficient silicon solar on a commercial basis.     

Oxygen-enrichment of YBa2Cu3 YBa2Cu3O7-δ using the fluidization techniqueusing the fluidization technique

The oxygen-deficient phase of the highT _c superconductor, YBa₂Cu₃O₇, was oxygen-enriched using the fluidization technique to give good superconducting properties. The normal method of oxygen treatment at 900°C for 24 h and at 600°C for 24 h has been reduced to just one treatment at 600°C for 12 h by the fluidization technique to achieve almost the same strength of superconducting signal for the YBa₂Cu₃O₇ powder, which establishes the attractiveness of the latter route for the large-scale preparation of superconducting material. The particle sizes were in the range 0–90, 90–180 and 180–420 μm. The fluidized particles were crystalline with orthorhombic distortion.T _c ^onset , estimated using the a.c. magnetic susceptibility method, was 91·3 K. The volume fraction of superconducting material in the product was 83·7–85·3%, one of the highest values reported so far for YBa₂Cu₃O₇.     

Oxygen inhomogeneities in YBa2Cu3O7−x single crystals withx>0.5 (oxygen inhomogeneities in YBa2Cu3O7−x …)

The microstructure of HTS YBa₂Cu₃O_7−x single crystals withx⩾0.5 has been investigated by TEM and selected area diffraction. An inhomogeneous oxygen distribution over the crystal was observed. Large differences between the bulk crystal structure and the surface have been established. The bulk structure was presented by orthorhombic blocks (≈100×10×20 nm in size) embedded in tetragonal matrix withx≈1. The bulk structure was not of a superconductive type. The crystal surface was enriched by oxygen and had the usual orthorhombic twinned structure. The superconductive properties of the whole specimen were determined by surface layer about 5 μm thick.     

Growth of gallium orthophosphate single crystals in acidic hydrothermal solutions

The hydrothermal growth of GaPO₄ single crystals has been studied in several solutions. Among many solutions, H₃PO₄, HCl and H₂SO₄ solutions were found to be effective solvents for the growth of GaPO₄ single crystals. Single crystals have been hydrothermally grown at temperatures over the range 210 to 290 °C in these solutions with seed crystals. HCl solution was found to be the most effective solvent in which to grow large single crystals. Morphologies of crystals grown at temperatures below 200 °C tended to be bounded by small major rhombohedral (1 0 ˉ1 1) faces. In the temperature range from 210 to 430°C, the crystals have morphologies bounded by prism (1 0 ˉ1 0), small major rhombohedral (1 0 ˉ1 1) and minor rhombohedral (0 1 ˉ1 1) faces, and grew with well developed basal (0 0 0 1) faces with increase in the growth temperature. Single crystals of GaPO₄ with lower dislocation density have been hydrothermally grown at 210 to 290°C in 3m H₃PO₄ solution.     

Deformation substructure in polycrystalline alumina

Transmission electron microscopy techniques were employed in a study of substructure in two sintered, 20μm alumina (≧99%Al₂O₃) bodies, each being examined in the as-annealed condition and after achieving 2% permanent strains in compression at 1420 and 1700° C. The as-sintered microstructures were found to contain dislocation networks which were often associated with intragranular porosity. Twinned structures of rhombohedral and basal types were also observed but were relatively infrequent. Amorphous second phases commonly located at triple points were characteristic of the less pure (99% Al₂O₃) material, and were also observed in the 99.9% purity material, but only in very limited amonts. The plastic deformation behaviour of these bodies at elevated temperatures (T ≦ 1420° C) illustrates that dislocation motion is an important mode of deformation in alumina. The observation of 〈11ˉ20〉 and 〈ˉ1011〉 glide dislocations further suggests that alumina can exhibit ductile behaviour at elevated temperatures. Grain boundary shearing was also observed to contribute to plastic deformation, being associated with either grain-boundary dislocations or interfacial impurities which can alter deformation behaviour. The author was a research associate in the Department of Engineering Research, North Carolina State University, during the course of this study. This work was sponsored by the US Atomic Energy Commission under Contract No. AT-(40-1)-3328. This paper is based on one portion of a thesis submitted for the Ph.D. degree in materials engineering at North Carolina State University, June 1970.     

SiC-ZrO2(3Y)-Al2O3纳米复相陶瓷的力学性能和显微结构

Heterogeneous precipitation methods were used to produce 5wt% SiC-15wt% ZrO₂(3Y)-Al₂O₃ nanocomposite powders. The aqueous suspension's pH controlled between 9 and 10, and the resulting gel calcined at 1000°C are two key processes for preparing nanocomposite powders. 5wt% SiC-15 wt% ZrO₂(3Y)-Al₂O₃ nanocomposites were superfast densified using spark plasma sintering (SPS) 妏rocess by heating to a sintering temperature between 1350 to 1600°C at a heating rate of 600C/min, without holding time, and then fast cooling to 600°C within 3 minutes. Bending strength of 5wt% SiC-15wt% ZrO₂(3Y)-Al₂O₃ nanocomposites sintered at 1450°C reached a value as high as 1200MPa, while the fracture toughness of the sample sintered at 1450°C was above 5MPa^1/2, which is significantly higher than that of SiC-Al₂O₃ nanocomposites and Al₂O₃ ceramics. Microstructure studies found that nano-SiC particles were mainly located within Al₂O₃ grains and the fracture mode of the nanocomposites was mainly transgranular fracture. It is the main reason why the intra-type nanocomposites show excellent mechanical properties, while in present research system, a part of contribution to high mechanical properties is from ZrO₂ phase transformation toughening.     

Electrosynthesis of conducting polyanilines in biphasic media

The electrochemical polymerization of aniline has been studied in the biphasic media. One phase comprises a polar medium containing some added electrolytes and the other a non-polar solvent containing the monomer. Ferric chloride has been used as the supporting electrolyte to catalyse the process of electropolymerization. Polyaniline was obtained in moderate yields with the highestR _p of 0·0237% per hour and a maximum polymerization efficiency of 61·65 ￠ 10⁻² mol/Faraday. The observations and experimental results suggest a cationic mechanism.     

Superconducting Bi-Sr-Ca-Cu-O films formed diffusion of metallic bismuth on Sr2Ca2Cu4O y substrates

Superconducting Bi-Sr-Ca-Cu-O films have been prepared on Sr₂Ca₂Cu₄O _y substrates by thermal evaporation of metallic Bi layer and heat-treatment at 830°C for a few minutes in air. The zero resistance temperature of Bi₂Sr₂Ca₁Cu₂O _y film of 1–μm in thickness is about 70 K. The surface diffusion process of Bi on the granular structure of Sr₂Ca₂Cu₄O _y was observed by scanning electron microscope and thermogravimetry analysis. The stripe pattern of superconducting film, typically 2μm thick and 0·3 mm wide, is formed by using a mask.     

Conventional Fabrication Method for TCNQ Radical Anion Salts Molecular Wires

NMP-TCNQ (NMP=N-methylphenazinium, TCNQ=7,7,8,8-tetracyanoquinodimethane) and (NEt₄)TCNQ gave molecular wires on a glass substrate by recrystallization from the acetone solution coexistence with the substrate. The width of the wires largely depends on the evaporation ratio of the solvent through recrystallization. When evaporating ratio of NMP-TCNQ solution was 167 μl/min, the width was minimized to 35 nm. Comparison of the IR spectra and XRD patterns with the corresponding single crystals clearly indicates that these wires have same crystallinity as the single crystals.     

Effect of bismuth replacement at barium site in Y-Ba-Cu-O system

X-ray diffraction, electron paramagnetic resonance, microwave absorption and resistivity measurements were carried out on YBa_2−x Bi _x Cu₃O₇ (0≤x≤0·5) superconductors in order to study the effect of bismuth on the structural and superconducting properties. A decrease in sintering temperature increased the amount of impurity phase. Transition from an orthorhombic (superconducting) phase to tetragonal structure produced no significant change in EPR zero-field signal at liquid nitrogen temperature (LNT). The non-resonance signal height decreased on higher concentration of bismuth. Sintered YBa_2−x Bi _x Cu₃O₇ superconductor had a strong EPR zero-field signal at LNT. We have evaluated particle size from XRD and EPR studies. The average particle size was about 0·4μm.     

YBa2Cu3O x superconducting thin films prepared by low temperature vacuum codeposition

Y-Ba-Cu-O films were prepared by low temperature codeposition of three components. The Y and Cu contents were evaporated from metallic sources, while Ba was vacuum-evaporated from Ba, BaO and BaF₂ sources in separate codeposition experiments. The lowest temperature at which superconducting YBa₂Cu₃O _x thin films (about 0.5μm thick) preparedin situ was near 500°C. This process enables preparation of superconducting films on various substrates (SrTiO₃, MgO, Al₂O₃, Si) without a buffer layer. Zero-resistance critical temperature was as high as 88 K and the critical current density was 10⁴ A/cm² at 4.2 K. The morphology of the films was granular with disordered grain orientation, the average grain size being typically 0.5μm.     

Preparation and Structural Characterization of Rapidly Solidified AI-Cu Alloys

Rapidly solidified Al_(100-x)—Cu_x alloys(x = 5,10,1 5,25,35 wt%) were prepared and analyzed.High cooling rate increased the Cu solubility in 9.-AI matrix.The influence of the cooling rate on Cu solubility extension in Al was experimentally simulated.Thus the pouring was performed in metallic die and by melt spinning-low pressure(MSLP) technique.Melt processing by liquid quenching was performed using a self-designed melt spinning set-up which combined the cooling technology of a melt jet on the spinning disc with the principle of the mold feeding from low pressure casting technology.The thickness of the melt-spun ribbons was in the range of30—70 μm.The cooling rate provided by MS-LP was within 10~5—10~6 K/s after the device calibration.The obtained alloys were characterized from structural,thermal and mechanical point of view.Optical microscopy and scanning electron microscopy were employed for the microstructural characterization which was followed by X-ray analysis.The thermal properties were evaluated by dilatometric and differential scanning calorimetric measurements.Vickers microhardness measurements were performed in the study.In the case of the hypereutectic alloy with 35 wt%Cu obtained by MS-LP method,the microhardness value increased by 45%compared to the same alloy obtained by gravity casting method.This was due to the extended solubility of the alloying element in the α-AI solid solution.     

Preparation, characterization and optical properties ofα-Fe2O3 films by sol-spinning process

α-Fe₂O₃ films were prepared by sol-spinning process using ferric nitrate as a precursor and 2-methoxy ethanol as the solvent. The films were grown on various substrates by spin coating and were subjected to different annealing temperatures. These were characterized using X-ray and fourier transform infrared spectroscopy (FTIR). The films showed crystallinity at about 500°C. The surface morphology of these films was studied using scanning electron microscopy (SEM) which revealed cracks for films having thickness of the order of 2 μm. The band gap of these films was observed to be 2·1 eV from UV-vis spectroscopy.     

Growth and Solvent Effects of a Promising Nonlinear Optical Sodium Paranitrophenolate Dihydrate (NO_2-C_H_4-ONa·2H_2O) Single Crystal

Sodium paranitrophenolate dihydrate (NPNa·2H2O) is an excellent semiorganic nonlinear optical (NLO) material, crystallizes both in water and methanol with high degree of transparency. Good optical quality single crystals of dimension upto 18 mm×6 mm×3 mm are obtained by isothermal solvent evaporation technique. The solubility of the crystal in different solvents was measured gravimetrically. The single crystals of NPNa·2H2O show variation in physical properties and growth rate in different solvents. Methanol or ethanol solution yields crystals of bipyramidal shape with clear morphology. However, methanol grown crystal is exhibiting improved hardness parameters and possesses excellent thermal stability as compared to water grown crystals. The effects of solvent on hardness parameter along with thermal and optical properties of NPNa·2H2O was revealed in this paper.     

Effect of temperature on the interaction of ÉP823 steel with lead melts saturated with oxygen

We study the corrosion behavior of ferritic-martensitic éP823 steel in a static lead melt, saturated with oxygen, at 550 and 650°C. At these temperatures, a complex magnetite-base scale is formed on the surface of steel, but the mechanisms of its growth are different. At 550°C, corrosion has a cyclic character. On the surface of steel, a Fe_1+x Pb_2−x O₄−Fe_1+x Cr_2−x O₄ two-layer scale is formed periodically. Reaching the critical thickness (18 μm), it exfoliates along the interface with the matrix, to which oxygen-containing lead penetrates, whereupon this process is repeated. The corrosion rate is ∼0.08 mm/year. At 650°C, the intensification of reactions of formation of chromium spinel and plumboferrite induces the growth of a porous scale, where lead is accumulated. This scale has good adherence to the matrix and is formed as a compact conglomerate owing to the efficient mass transfer at all interfaces, which leads to a catastrophic rate of thinning of the specimen (3.82 mm/yr) in a lead melt. On the basis of experimental data, we propose schemes of the oxidation of chromium steels in a lead melt with a high oxygen activity at different temperatures. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 2, pp. 77–84, March–April, 2007.     

Shape-forming and densification of ceramic superconductors

Processing studies on varied shape-forming and densification of bulk ceramic superconductor, YBa_1·5Ca_0·5Cu₃O_7\t-\gd, are reported in this paper. Polyvinyl butyral-polyethylene glycol-trichloroethylene has been found to be the best binder-plasticizer-solvent system in plastic shape-forming. The effect of initial particle morphology on final densification has been the most sensitive single parameter as compared to compaction pressure and final sintering durations at ∼930°C. 1-2-3 powders of mean particle size ∼ 1·94 μm have yielded sintered densities ∼92% T.D. albeit with lower oxygen intake O_6·7.     

The preparation and microwave properties of Ba3ZnZCo2-ZFe24O41/SiO2 microcrystalline glass ceramics by citrate sol-gel process

A series of Ba₃Zn_ZCo_2-ZFe₂₄O₄₁/SiO₂ microcrystalline glass ceramics with Z=0.0,0.4,0.8 and 1.2 were prepared by citrate sol-gel process. The result showed that Ba₃Zn_ZCo_2-ZFe₂₄O₄₁ hexferrite crystallites could be obtained by this process at 1200 °C in the system of BaO-Fe₂O₃-CoO-ZnO-SiO₂. The complex dielectric constant and complex permeability of Ba₃Zn_ZCo_2-ZFe₂₄O₄₁/SiO₂ microcrystalline glass ceramics calcined at different temperature were measured in the range of 200MHz-6 GHz by transmission/reflection coaxial line method. The complex dielectric constant and dielectric loss exhibited insignificant variety in the whole range of measuring frequencies for all samples. The real part of the permeability decreased as the measuring frequency increasing, and calcining temperature had a clear influence on the value of μ′ for Ba₃Zn_ZCo_2-ZFe₂₄O₄₁/SiO₂ microcrystalline glass ceramics, and so did the content of Zn²⁺ and Co²⁺. The natural resonance phenomenon was observed in μ′′ spectra for all the Ba₃Zn_ZCo_2-ZFe₂₄O₄₁/SiO₂ microcrystalline glass ceramics. The substitution of Zn²⁺ ion and annealing temperature closely affect the resonance frequency, the more the Zn²⁺ ion, the higher the annealing temperature and the lower the resonance frequency. Received: 23 July 2001 / Accepted: 24 July 2001     

Thick film adherence fracture energy: influence of alumina substrates

The adherence of a glass bonded Pt-Au thick film conductor to various alumina substrates is degraded by changes in the surface composition of and by the presence of (0001) crystallographic texture in the substrate. Using the critical fracture energy (γ_IC) required to separate the thick film from the substrate, it was found that γ_IC was reduced from a maximum of 3.7 J m⁻² using an as-received 96+ wt% alumina substrate to ∼2J m⁻² using an as-received 99+ wt% alumina. In addition, the thick film adherence γ_IC using (0001) sapphire substrates was less than that using (11ˉ23) sapphire. The 96 wt% substate exhibited essentially a random crystallographic surface texture and a considerable amount of surface silicates. The as-received 99+ wt% Al₂O₃ substrate was charactarized by a high (0001) surface texture and, while exhibiting a similar composition silicate layer as that of the as-received 96 wt% alumina, the total amount of the glass layer is greatly diminished. Fractographic analysis of the separated thick films and substrates showed that changes in the substrate crystallographic texture and the glass layer diminish the interpenetrating nature of the glass—metal interface and weaken the glass—substrate interface. Such changes in thick film microstructure lead to poorer thick film adherence.     

Interface reactions between titanium thin films and (1¯1 2) sapphire substrates

We have studied the reactivity of Ti with the R-plane (1ˉ1 2) of sapphire from room temperature to 1250 °C by X-ray photoemission spectroscopy (XPS), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Rutherford backscattering spectroscopy (RBS). The combination of these techniques allowed the interface reactions to be studied from the monolayer regime up to the bulk regime. XPS showed that at room temperature, monolayer coverages of Ti reduced the sapphire surface to form Ti-O and Ti-Al bonds. TEM, XRD, and RBS showed that annealing of room-temperature deposited Ti resulted in an interfacial region consisting of two layers, a Ti₃Al[O] layer adjacent to the sapphire and a Ti_0.67 [O_0.33] layer at the free surface. The growth of the Ti₃Al[O] layer had an activation energy of 103.4±25 kJ deg-mole. The nature of the interfacial reaction between Ti and sapphire was similar for Ti coverages from the monolayer to the bulk regime.     

Preparation of Gd2O2S:Pr Scintillation Ceramics by Pressureless Reaction Sintering Method

Fabrication of Gd₂O₂S:Pr scintillation ceramics by pressureless reaction sintering was investigated. The 2Gd₂O _3˙(Gd,Pr)2(SO ₄)_3˙mH₂O precursor was made by hydrothermal reaction using commercially available Gd₂O₃, Pr₆O₁₁ and H₂SO₄ as the starting materials. Then single phase Gd₂O₂SO₄:Pr powder was obtained by calcining the precursor at 750°C for 2 h. The Gd₂O₂SO₄:Pr powder compacts can be sintered to single phase Gd₂O₂S:Pr ceramics with a relative density of 99% and mean grain size of 30 μm at 1750°C for 2 h in flowing hydrogen atmosphere. Densification and microstructural development of the Gd₂O₂S:Pr ceramics were examined. Luminescence spectra of the Gd₂O₂S:Pr ceramic under 309 nm UV excitation and X-ray excitation show a green emission at 511 nm as the most prominent peak, which corresponds to the ³P₀-³H₄ transition of Pr³⁺ ions.