Physics
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Item Electrolyte Electroreflectance Study of CdIn2Se4 Liquid Junction Solar cells(American Physical Soc. Meeting, Los Angeles,USA, 1983) Tomkiewicz M; Siripala WItem The Interrelation Between the Potential Distribution and the Dark Charge Transfer Across n-TiO2 - Aqueous Electrolyte Interface(Symposia on Photoelectrochemical Process and Measurements Techniques for Photoelectrochemical Solar Cells, 1981) Tomkiewicz M; Siripala WItem Surface States at CuInSe2/Aqueous Electrolyte Interface(Journal of Science of the University of Kelaniya Sri Lanka, 1997) Siripala WImpedance measurements were used to evaluate the relative band edge positions of single crystal p-CuInSej electrodes in aqueous 0.1M IQS04 solution by measuring die extrapolated flat-band potentials, Vf t . We find that Vf t can be shifted by oxidation and reduction of the electrode surface and this observation was verified by chopped light current-potentialmeasurements. The surface state density distribution responsible for this shift was evaluated and found that it islocated at 0.43 eV above the valence band with a peak density of 3x101 4 eV'1 cm' 2 and it could be removed by electrochemical reductionItem Band Edge Shifts of p-type Copper Indium Diselenide Electrodes in Aqueous Electrolytes(Applied Physics Letters, 1993) Siripala W; Vedel, J.; Lincot, D.; Cahen, D.Impedance measurements were used to evaluate the relative band edge positions of single crystalp?CuInSe2electrodes in various aqueous electrolytes, by measuring the extrapolated flatband potentials, V fb. We find that V fb can be shifted, depending on the extent of the potential scan and on the pH of the electrolyte used, over a range of up to 1.7 V (between pH 0?pH 14). In the pH range 0?6, V fb can be fixed at intermediate values, which, in their turn, are determined by the pH of the electrolyte.Item A Photoelectrochemical Investigation of n- and p-type semi�conducting behaviour of Copper Oxide Films(Semiconductor Science and Technology, 1989) Siripala W; Kumara K PCopper(I) oxide films were prepared on copper substrates by exposing them to solutions containing Cu2+ ions, and it was observed that the photoresponse of these films electrodes in a photoelectrochemical cell is both n- and p-type. However, it was observed that the n-type behaviour of these film electrodes could be enhanced and the p-type behaviour could be reduced by adjusting the pH of the solution in which the oxide films had been prepared. The simultaneous existence of spatially separated n- and p-type regions in the Cu2O film is suggested as the possible reason for these observations. The anodic oxidation of copper was considered to be the origin of the p-type regions while the n-type regions were considered to be the result of the cathodic deposition of Cu2O.Item Characterization of Surface States at a Semiconductor Electrolyte Interface by Electroreflectance Spectroscopy(Journal De Physique, 1983) Tomkiewicz M; Siripala WSupra bandgap and subband gap Electrolyte Electroreflectance is being used to characterize surface states at semiconductor liquid interfaces. The surface states can manifest themselves either through direct optical transitions as in the case of n - TiO2 - aqueous electrolyte interface or through their effect on the response of the Fermi level to small changes in the electrode potential as in the case of single crystal CdIn2Se4 in polysulfide solutions.Item Spectral responses of electrodeposited cuprous oxide thin film electrodes(Journal of the National Science Council of Sri Lanka, 1995) Siripala WPhotoresponse of the electrodeposited cuprous oxide thin film electrodes were investigated in a photoelectrochemical cell. Spectral response measurements reveal that a Schottky-type junction is formed at the junction between the substrate and cuprous oxide resulting in n-type and p-type photosignals in a photoelectrochemical cell. The electrodeposited cuprous oxide is an n-type semiconductor.Item Photovolatic properties of Cu2O/CuxS heterojunction(Journal of the National Science Council, Sri Lanka, 1990) Siripala W; Kumara K PA simple electrochemical method was developed to fabricate a Cu2O/CuxS heterojunction and it was then used in preparing a thin film photovoltaic soar cell. Cu2O was prepared by the method of electrodeposition and CuxS was coated on Cu2O by a simple dipping method. The photovoltaic properties of the cell could be improved significantly by heat treatment in air. The maximum conversion efficiency of the cell was 0.1% and V oc = 180mV and I sc = 2.0mA/cm2 under A M 1 artificial illumination.Item Optical Investigation of the Electrodeposited Cuprous Oxide Film Electrodes using Photocurrent Spectroscopy(1986) Siripala WThermally grown Cuprous Oxide has known as a p-type semiconductor and the p-type conductivity is attributed to the Copperion vacancies created in the crystal lattice during the oxide formation. However, we have observed, for the first time, that the cathodically deposited Cu2O films on various metal substrates produce n-type photoconductivity. Photoelectrodes were used in a photoelectrochemical call containing an aqueous electrolyte. Photocurrent-potential behaviour demonstrate that the photoresponse is anodic and the analysis of the spectral response measurements reveal thet Cu2O has a direct bandgap of 2.0 eV. Tenactive assignment of Oxygen ion vacancies in the electrodposited cupprous Oxide films, which would result in n-Cu2O, is proposed.Item Electrolyte electroreflectance study of surface optimization of n-CuInSeâ in photoelectrochemical solar cells(Journal of Electrochemical Society, 1986) Shen, Wu-Main; Siripala W; Tomkiewicz, M.; Cahen, D.Electrolyte electroreflectance is used to show that the main effect of Br2/MeOH etching of CuInSe2 is to remove the pinning of the Fermi level, which is due to a monolayer of states located 0.17V positive to the potential of CuInSe2 the solution. The flatband potential of in polysulfide solution was found to be ?0.62V vs. the solution potential, while in polyiodide solution it is shifted to ?0.70V vs. the potential of that solution. This shift can explain some of the improvement in performance in polyiodide compared to polysulfide. The bandgap of CuInSe2 was found to be a direct transition at 1.01 eV with a three?dimensional critical point.