P.J. Sebastian

Studies on the oxygen reduction catalyst for zinc-air battery electrode

Abstract In this paper, perovskite type La 0.6 Ca 0.4 CoO 3 as a catalyst of oxygen reduction was prepared, and the structure and performance of the catalysts was examined by means of IR, X-ray diffraction (XRD), and thermogravimetric (TG). Mixed catalysts doped, some metal oxides were put also used. The cathodic polarization curves for oxygen reduction on various catalytic electrodes were measured by linear sweep voltammetry (LSV). A Zn–air battery was made with various catalysts for oxygen reduction, and the performance of the battery was measured with a BS-9300SM rechargeable battery charge/discharge device. The results showed that the perovskite type catalyst (La 0.6 Ca 0.4 CoO 3 ) doped with metal oxide is an excellent catalyst for the zinc–air battery, and can effectively stimulate the reduction of oxygen and improve the properties of zinc–air batteries, such as discharge capacity, etc.

Influence of the hydrophobic material content in the gas diffusion electrodes on the performance of a PEM fuel cell

In the present study the influence of the hydrophobic material (Teflon, polytetrafluoroethylene) content in the gas diffusion electrodes (anode and cathode) on the performance of a H 2 /O 2 proton exchange membrane fuel cell is reported. The potential-current (E-I) evaluation of the fuel cell indicated that a combination of 10 and 30 wt% of Teflon, respectively, in the cathode and anode gave the best results.

Compositional and optoelectronic properties of CIS and CIGS thin films formed by electrodeposition

Abstract CuInSe2 (CIS) and Cu(In,Ga)Se2 (CIGS) thin films were prepared by electrodeposition and processing. The influence of film deposition parameters such as bath composition, pH, deposition potential and material purity on film properties was studied. The structural, morphological, compositional and opto-electronic properties of electrodeposited and selenized CIS and CIGS thin films were characterized using various techniques. As-deposited as well as selenized films exhibited a compact or a granular morphology depending on the composition. The film stoichiometry was improved after selenization at 550°C in a tubular furnace. The films are formed with a mixed phase composition of CuInSe2 and CuIn2Se3.5 ternary phases.

Optical properties of electrodeposited CdTe thin films

Abstract The absorption coefficient spectra of the elctrodeposited CdTe thin films were analyzed and compared with that of the single crystal. Pinhole-free thin films facilitated the analysis of the high-energy regions of the absorption coefficient spectra. The various allowed direct and indirect transitions were detected successively by subtracting the extrapolated values of the lower-energy transitions. The effect of heat treatment on the optical transitions were analyzed with films annealed at 300°C in air, argon and CdCl 2 .The direct band gap of the electrodeposited films decreased with increasing film thickness and approaches the value of the single crystal. The films annealed at different environments show slightly lower value for the band gap. Annealing in argon caused significant change in the optical transition spectra.

CIS and CIGS based photovoltaic structures developed from electrodeposited precursors

Abstract In the present study we report the electrodeposition and characterization of CIS and CIGS thin films and a post-deposition thermal processing in vacuum to improve the film stoichiometry by incorporating additional In, Ga and Se. Different kinds of analyses showed that CIS as well as CIGS possess a very thin In-rich surface n-layer. The formation and characterization of solar cell structures from the electrodeposited precursor with the configuration glass/Cr/Mo/CIS(CIGS)/CdS/ZnO/MgF 2 is also reported. The optoelectronic properties such as Voc, Isc, FF, η etc. of the cells are presented.

Optical, electrical and structural investigations on Cd1-xZnxSe sintered films for photovoltaic applications

II–VI polycrystalline semiconducting materials have come under increased scrutiny because of their wide use in the cost reduction of devices for photovoltaic applications. Cd1−xZnxSe is an important semiconducting alloy because of the tunability of its physical parameters such as band gap and lattice parameters by controlling its stoichiometry. Many more material characteristics of it would be altered and excellently controlled by controlling system composition x. Polycrystalline thin films of Cd1−xZnxSe with variable composition (0⩽x⩽1) have been deposited onto ultra-clean glass substrates by sintering process. The optical, structural and electrical transport properties of Cd1−xZnxSe thin films have been examined. The optical band gap and optical constants of these films were determined by using double beam spectrophotometer. The DC conductivity and activation energy of the films were measured in vacuum by two-probe technique. The Schottky junction of Cd1−xZnxSe with indium was made and the barrier height and ideality factor were determined using current–voltage characteristics. The nature of sample, crystal structure and lattice parameters were determined from X-ray diffraction patterns. The films were polycrystalline in nature having cubic zinc-blende structure over the whole range studied. Sintering is very simple and viable compared to other cost intensive methods. The results of the present investigation will be useful in characterizing the material, Cd1−xZnxSe, for its applications in photovoltaics.

Fundamental studies on large area Cu(In,Ga)Se2 films for high efficiency solar cells

This work reports the growth and characterization of thin films of Cu(In,Ga)Se2 (CIGS), which were grown by sequential sputtering, electrodeposition, and physical vapor deposition. Photovoltaic cells have been fabricated using these films with CdS heterojunction partners and the performance has been characterized. The effect of annealing conditions (temperature and duration) on the CIGS film microstructure and corresponding device performance has been investigated. Structure-property correlations were made using diffraction studies and Rietveld analysis. SEM studies were carried out to understand the effect of microstructure of the CIGS films on the solar cell efficiency. Cell efficiencies in excess of 10% have been achieved by using optimized annealing conditions. In addition, the optical properties of the sputtered CIGS films were characterized using variable angle spectroscopic ellipsometry and sputtered CIGS films were found to have optimum band gap. r 2001 Elsevier Science B.V. All rights reserved.

Electrodeposited and selenized (CuInSe2) (CIS) thin films for photovoltaic applications

Abstract In the present communication, the authors report results on the characterization of electrodeposited and selenized (CuInSe 2 ) (CIS) thin films. The selenization process was carried out using a technique called chemical vapor transport by gas (CVTG). The precursors as well as selenized films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron microprobe analysis (EPMA). The film stoichiometry improved after selenization at 550°C. The films were formed with a mixed composition of the binary as well as the ternary phases.

A CdTe/PMeT photovoltaic structure formed by electrodeposition and processing

CdTe thin films were electrodeposited from an ethylene-glyco-based bath by the galvanostatic method. As-deposited and tellurized films were characterized by structural, optoelectronic and photoelectrochemical methods. The film stoichiometry improved after tellurization of the film at 300°C by a technique called chemical vapor transport by Gas (CVTG) in a tubular furnace. Tellurized films showed near stoichiometry with p-type conductivity in the bulk and n-type surface conductivity. Schottky barrier type photovoltaic junctions were obtained using a heavily doped PMeT (poly-3(methylthiophene), prepared by electropolymerization, displaying nearly metallic behavior, and CdTe obtained by electrodeposition. A solar to electrical conversion efficiency of the order of 1% was obtained in the case of PMeT/CdTe junction.

Photoelectrochemical characterization of porous Si

Abstract The photoelectrochemical measurements of p-Si and porous silicon in 0.1 M H2SO4 were done. The band gap of Si is a bit low for efficient hydrogen production. The silicon was made porous to improve the efficiency of hydrogen production. The porous silicon photocathodes show a substantial improvement in the hydrogen production compared to that of p-Si photocathodes. Studies were done by applying different light flux on the porous silicon.