Effect of a Mo back contact on Na diffusion in CIGS thin film solar cells

We investigated the effects of the microstructures of molybdenum (Mo) back contacts on sodium (Na) diffusion from sodalime glass into a Cu(In,Ga)Se₂ (CIGS) absorber as a function of the sputter deposition pressure during preparation of the Mo contact layer. The surface characteristics of the Mo layers more significantly affected the diffusion of Na ions into the CIGS compared with the Mo bulk. The Na ion diffusion depended strongly on the amount of oxygen adsorbed onto the Mo layer surfaces. Secondary ion mass spectroscopy results showed that Na accumulated in a layer (Na–O compound) on the Mo surface (the CIGS/Mo interface), and this layer served as a primary source of Na ions diffusing into the CIGS. A trilayered Mo back contact structure was prepared in an effort to decouple the functions of electrical conductance and Na diffusion. The ability of this surface to control the Na concentration in a CIGS absorber is discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Figure of Merit of Composite Filters with Micrometer and Nanometer Fibers

We investigate the filtration performance of composite filters composed of micrometer and nanometer fibers. The filter quality is evaluated using the figure of merit, also known as the quality factor. We use analytical expressions for the pressure drop and filtration efficiency to compute the figure of merit. The effects on the figure of merit by fiber diameter, solidity, and thickness of nanometer and micrometer fibers and face velocity are investigated. Experimental data obtained using conventional filter media and nanofiber composite filters are then used to verify the calculated results. We find that for large particles (approximately 0.1 μm and above), nanofibers can improve the figure of merit compared to conventional filters. Smaller fiber size, larger solidity, and thickness of the nanofiber layer lead to better filtration performance in this size range. For small particles (approximately below 0.1 μm), nanofibers do not improve the figure of merit compared to conventional filter media. Larger fiber size, smaller solidity, and thickness of the nanofiber layer are preferred in this size range. We demonstrate that our procedure using analytical expression is a fast and effective tool for filter media design.     

Electrical characteristics of thermally stable Ru and Ru/Au ohmic contacts to surface-treated p-type GaN

The electrical and thermal properties of Ru and Ru/Au ohmic contacts on two-step-surface-treated p-GaN have been investigated using current-voltage (I–V) measurements and Auger electron spectroscopy. It is shown that annealing at 700°C for 2 min in a flowing N₂ atmosphere improves the I–V characteristics of the contacts. For example, the annealed Ru and Ru/Au schemes produce a specific contact resistance of 3.4 (±0.9)×10⁻³ and 1.2 (±1.1)×10⁻³ Ωcm², respectively. It is also shown that annealing results in a large reduction (by ∼100 meV) in the Schottky barrier heights of the Ru and Ru/Au contacts, compared to the as-deposited ones. The electrical properties of the two-step-surface-treated Ru/Au contacts are compared with those of the conventionally treated contacts.     

Study on the soldering in partial melting state (1) analysis of surface tension and wettability

This paper introduces the partial melting process for solder application and characterization of its feasibility using Pb-Sn, Ag-Sn, Sn-Cu, Sn-In and Sn-Bi alloys. In order to show that the liquid phase in the semi-liquid state maintains the similar wettability as the single-phase liquid, the wetting balance tests are conducted with varying temperatures and compositions. The results are then compared with the surface tension of liquid, both measured and calculated, to examine the correlation. The results from this investigation indicate that the partial melting can yield satisfactory solder joints as long as the liquid phase acquires sufficient chemical activity. At a condition where the partial melting is effective, a direct correlation between the wettability and the surface tension is found to exist. All alloys except two, Sn-Bi and Sn-In, are found to show a reasonable wettability in semi-liquid state.     

Inkjet printed electronics for multifunctional composite structure

Copper nano-ink with a drop-on-demand (DOD) piezoelectric inkjet printing method was introduced. The printed electrodes were thermally sintered to ensure high-quality electrical and mechanical performances. To check the reliability of the printed electrodes on a polymer layer, resistance changes were measured under static loading. The electrodes with various widths and thicknesses were used to find the optimal dimensions. A multifunctional composite laminate which can harvest and store a solar energy was fabricated using printed electrodes. An amorphous silicon solar cell and a thin film solid state lithium-ion battery were adhesively joined and electrically connected to a thin flexible printed circuit board (PCB). Then, the passive components such as resistor and diode were electrically connected to the printed circuit board by silver pasting. The integrated PCB was co-cured with a carbon/epoxy composite laminate by the vacuum bag molding process in an autoclave. The structural and functional performance of the final energy harvesting/storage composite laminate was tested under mechanical loading.     

Electrical properties and microstructural characterization of single ZnO nanowire sensor manufactured by FIB

The devices using individual ZnO nanowire have been manufactured by FIB. Its specific resistance and microstructural characterization has been investigated using nano manipulator and transmission electron microscopy (TEM) observations. The specific resistance was 0.2-0.4 Ω cm. With increasing the RTA temperature, the specific resistance began to be decreased and was abruptly decreased at the RTA temperature above 500 °C. The Pt junction of as-manufactured device consisted of the Pt nanoparticles of 5 nm and the amorphous carbon of 9.1 wt.%. After RTA, the size of Pt nanoparticles grew up to 100 nm, the contents of carbon were decreased within the Pt junction, and the conductivity was enhanced due to Au diffusion into the Pt junction. It was strongly suggested that the contents of carbon is the most important factor for the electrical enhancement.     

Effects of maleination and heat treatment on morphology and dynamic mechanical thermal behavior of polypropylene/organoclay nanocomposites

Effects of maleinated compatibilizer and heat treatment on the internal structure and physical properties of PP/organoclay nanocomposites were investigated by using various measurements, e.g., SAXS, TEM, DSC and DMTA, and rotational rheometer. Experimental results showed that maleination and heat treatment affected the internal structure and dynamic mechanical properties of PP/organoclay nanocomposites. Storage modulus and loss tangent of PP/organoclay nanocomposites were strongly related to the compatibilizer loadings and heat treatment conditions because the interfacial structure between PP molecular chains and organoclay particles had been changed by the addition of compatibilizer to PP/organoclay nanocomposites. DSC and DMTA results of the compatibilized nanocomposites and effects of heat treatment on crystallization and dynamic mechanical thermal properties demonstrated that there is a small change in the glass transition temperature because the chain mobility and free volume in the amorphous region are increased by heat treatment. It was found that heat treatment imposed influence on both amorphous and crystalline regions of PP/organoclay nanocomposites.     

Adsorption of urokinase by polypropylene films with various amine groups

Polypropylene films with various amine groups were prepared by radiation‐induced grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) films and the subsequent amination of poly‐GMA graft chains were examined. The physical and chemical properties of the GMA‐grafted PP film and the aminated PP film were investigated by IR, SEM, XPS, and TGA. The adsorption of urokinase for the PP films modified with various amine groups was examined under various conditions of different amine group contents and pH values. The adsorption of urokinase increased by increasing the amine group content. In the range of amine group content from 1.0 to 2.7 mmol/g, the adsorption of urokinase by the PP films modified with six kinds of amines was in the following order: trimethylamine > diethylenetriamine > triethylenetetraamine > ethylenediamine > dimethylamine > diethyleneamine. The adsorption amounts of urokinase by the PP film with the trimethylamine and triethylenetetraamine groups at pH 7.4 were higher than those at pH 9. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2851–2858, 2001     

Improved surface characteristics and the conductivity of polyaniline–nylon 6 fabrics by plasma treatment

The effect of plasma treatment on the surface characteristics and conductivity of polyaniline–nylon 6 composite fabrics was investigated. Plasma surface modifications with oxygen, ammonia, and argon were performed on the nylon 6 fabrics to improve the adhesion and rate of polymerization. The surface morphology of the fiber was observed with scanning electron microscopy, and functional groups introduced onto the surface of nylon 6 fibers by various plasma treatments were characterized by X‐ray photoelectron spectroscopy. With oxygen plasma treatment, the fiber surface was effectively etched; polar groups such as ? OH and ? OOH were introduced onto the surface of nylon 6 fiber, and they increased surface activity, promoted oxidation polymerization, and resulted in higher add‐on and electrical conductivity. However, the introduced amine and amide groups with ammonia treatment caused a reduction in conductivity. Argon did not significantly alter the surface characteristics of the nylon 6 fibers. In addition, to control fabric conductivity and cover as wide a range of conductivity as possible, we observed the effects of the monomer concentration and number of deposits on the fabric conductivity. The results showed that fabric conductivity increased as the monomer concentration increased up to 0.5M and then leveled off, and further increases were achieved with an increase in the number of multiple deposits. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 684–694, 2001