Solid State Phenomena Vols. 124-126

Abstract: In order to enhance the electrochemical performance of lithium metal as an anode of lithium secondary battery, we prepared DLC film coating with various morphologies using a radio-frequency chemical vapor deposition method. Raman spectroscopy and FT-IR analyses revealed that the DLC film consists of mixture of graphitic sp2 and aliphatic sp3 hybridized bonds. DLC coating on lithium metal electrode play an important role as a passive layer during electrochemical reaction. Based on experimental results, we expected that the well dispersed DLC film coating sector as small as possible on the lithium metal electrode exhibits excellent electrochemical performance such as irreversible capacity and cycling performance.

Abstract: In this work, we report on the last investigation of POP (selective Phosphorous doping and contact Opening Process) in crystalline silicon solar cells. For the industrial solar cells, it must be very highly doped to decrease the high-contact resistance and not very shallow so that it is not perforated during paste firing, which would short-circuit the junction. We made improvement involves making separate diffusions for the different regions since the requirements are so different: a heavily doped and thick region under the contacts, a thin and lowly doped region under the passivating layer. Furthermore we opened the metal contact area to make a narrow grid lines simultaneously. As a result we could increase fill factor and reduce contact resistance by industrial process.

Abstract: In this paper, we present results of an investigation on the physical, mechanical, chemical properties and processing ability of the Cr2AlC ternary carbide bulk material synthesized by hot pressing technique. The combination of excellent properties indicated that Cr2AlC ternary carbide alloy could be potential candidate materials as bipolar plates in polymer membrane fuel cell (PEMFC).

Abstract: Cu(In1-xAlx)Se2 films were prepared using a two-stage process of sputtering and selenization. Stacked elemental layer precursors of Cu, In and Al were deposited onto corning glass substrates by RF magnetron sputtering. Precursors with different Cu/(In+Al) and In/Al ratio were selenized using elemental Se-vapor at atmospheric pressure in a commercial tube furnace under constant argon gas flow. Films with good adhesion to the substrate were grown successfully. All of the films show strong (112) and (220)/(204) CIS peaks. Addition of Al, at expense of In, shifts the peaks towards higher 2θ. This paper explores the possibility to use sputtering deposition and selenization process to grow Cu(InAl)Se2 thin films for solar cells applications.

Abstract: In order to more improve the performance of the existing P3HT:C60 polymer photovoltaic cells, we adopted soluble C70 insteade of C60. The absorption spectra of soluble C70 showed a significant increase of visible range absorption, resulting in the enhanced photocurrent. To optimize the device fabrication, we controlled the solvent, concentration of polymer solution and the thickness of photo-active layer. The best power conversion efficiency obtained in our P3HT:C70 photovoltaic cells was about 3.0 % under AM 1.5G condition.

Abstract: Co1-xFexSb3 skutterudites were synthesized by encapsulated induction melting and their thermoelectric properties were investigated. Single phase δ-CoSb3 was successfully obtained by the subsequent heat treatment at 773K for 24 hours in vacuum. However, δ-CoSb3 was decomposed to FeSb2 and Sb when x≥0.3, which means that the solubility limit of Fe to Co is x<0.3. The positive signs of Seebeck coefficients for all Fe-doped specimens revealed that Fe atoms acted as p-type dopants by substituting Co atoms. Thermoelectric properties were remarkably enhanced by Fe doping and optimum composition was found to be Co0.7Fe0.3Sb3 in this study.

Abstract: Branched sulfonated poly(ether ketone sulfone) copolymer was prepared from1,1,1- tris(4-hydroxyphenyl) ethane, 4,4-difluorophenylsulfone, 3,3'-disodiumsulfonylbenzophenone (40 mol% of bisphenol A) and bisphenol A by polycondensation with the elimination of water in toluene and NMP at 160) in the presence of anhydrous potassium carbonate. Composite membranes were successfully cast from the control of organic polymer with SiO2 4-10 wt% of polymer in DMSO. The films were converted from the salt to acid forms with dilute hydrochloric acid. Organicinorganic composite membranes for operation in polymer electrolyte membrane fuel cells (PEMFCs) were characterized and cell-tested. The physico-chemical properties of all membranes were investigated their thermal properties, water uptake, DSC and thermogravimetric analyzer (TGA). Branched copolymer and nano composite membranes exhibit proton conductivities from 1.7x10-3 to 8.3x10-3 S/cm2, water uptake from 22 to 26%, IEC from 1.28 to 1.46 meq/g and methanol diffusion coefficients from 1.2x10-7 to 1.7x10-7 cm2/S.

Abstract: In this study, mixed active material electrodes, composed of an activated carbon (MSP20) and LiCoO2, were prepared as cathodes for a high-capacitive hybrid capacitor. The electrochemical properties of (MSP20+LiCoO2)/Li cells were examined in terms of the weight composition and the particle size of LiCoO2 powder in the electrodes. As adding more LiCoO2 powders in the electrode, the volumetric capacity (mAh/ml) of the electrode became higher. In order to examine the size effect on the electrochemical performance, the LiCoO2 powders were modified by ball milling. The (MSP20+LiCoO2)/Li cells using 10 and 20 wt.% of 30h-milled LiCoO2 powder exhibited the lower internal resistivities and the better capacity retentions after 100 charge-discharge cycles than those using 10 or 20 wt.% of raw LiCoO2 powders.

Abstract: Fine Ti5Si3 powder has been synthesized from a mixture of elemental Ti and Si powders using a mechanochemical method. It shows a good catalytic effect on NaAlH4 by reducing the dehydrogenation temperature and improving the dehydrogenation kinetics. Although the catalytic effect of Ti5Si3 is not better than that of TiCl3, the Ti5Si3 catalyst has an advantage over TiCl3 in terms of hydrogen capacity by releasing more hydrogen than TiCl3 during dehydrogenation. NaAlH4 catalyzed with Ti5Si3 shows reversible hydrogen storage by being hydrogenated at moderate conditions, although the hydrogenation kinetics is rather slow.

Abstract: Lithium cobalt oxide is synthesized by a novel solution combustion procedure. In this synthesis, a solution mixture of lithium nitrate, cobalt nitrate and glycine fuel is heated to 500, 600 and 700 °C for 3 hours to obtain an ordered crystalline-layered compound. Physical properties of the synthesized cathode materials were evaluated using a XRD, SEM and particle size analyzer. The charge-discharge cycling characteristics of the synthesized lithium cobalt oxide heated at 700 °C exhibited better performance than other materials.