Physics
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Item Water splitting by electrodeposited cuprous oxide photoelectrodes with a flower like morphology(Annual Research Symposium-University of Kelaniya, 2011) Ranasinghe J I; Siripala WMorphology of semiconductor films plays a major role in determining the efficiency of solar cell devices. Intrinsic electronic properties of cuprous oxide (Cu2O) are important for water splitting reaction using solar energy to produce environmentally clean hydrogen fuel. Especially, the n-type cuprous oxide thin films with flower-like morphology have an added advantage for efficient water splitting. In this study electrodeposition of Cu2O thin films using an aqueous H2O2 bath was investigated for the possibility of depositing films on Ti substrates with a flower-like morphology. Direct deposition of Cu2O films on a Ti substrate using a H2O2 bath is not possible. However, it was found that if a thin Cu2O film was deposited using an acetate bath prior to the film deposition, good films with a flower-like morphology can be electrodeposited. In this study, Cu2O thin films were deposited on Ti substrates in a bath containing 0.1M CuSO4 and 0.3M H2O2 at 600C. pH value of the bath was kept at 4 by adding few drops of dilute NaOH solution. SEM pictures show the flower ?like morphology of the films. V-I characteristics and the spectral responses confirmed the n-type behavior of the deposited films. Possibility of water splitting using n-type Cu2O films without applying an external bias is demonstrated in this study. The performance of the films in a photoelectrolytic solar cell with a flower like morphology is compared with the films with normal morphology.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 Electrodeposited Cuprous oxide for low cost soalr energy Applications(International Conference on Solar Energy Materials, Solar Cells and Solar Energy Applications, Kandy, Sri Lanka, 2011) Siripala WCuprous oxide (Cu2O), one of the earliest known semiconductor materials, is attractive for solar energy applications because it is low cost, non toxic and has a direct band gap of 2 eV. It is considered as one of the candidate materials for the applications in the third generation of solar cells. Cu2O is generally a p-type semiconductor material due to the Cu vacancies exist in the crystal lattice. Earlier attempts to fabricate efficient thin film solar cells with this material were unsuccessful because the unavailability of n-type Cu2O. However, it has been reported that corrosion layers on Cu electrodes in aqueous baths produce n-type films. We have exploited this growth mechanism of n-type Cu2O films to electrodeposit n-type films on various conducting substrates. This technique of electrodeposition is attractive because it provides a low cost method for growing thin films, in addition to the n-type behavior. We found that a narrow potential window is available for the electrodeposition of Cu2O thin films. Also the conductivity type of the films is very sensitive to pH of the aqueous bath. Single phase Cu2O polycrystalline films can be obtained in the narrow potential domain and at more negative depositing potentials co-deposition of Cu is resulted. Cu2O thin films can be obtained by this method to produce n-type conductivity. This n-type behavior and the quality of the Cu2O films produced by the technique will be presented. Further, evidence for the existence of oxygen vacancies in the electrodeposited n-type Cu2O films is presented. Possibility of application of these n-type films in low cost solar cell devices is demonstrated with the n-Cu2O/p-CuxS junction obtained by sulphiding Cu2O thin films and with other junction formations.Item 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.