Physics
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Item Electrodeposition of n-type Cuprous Oxide Thin Films(Electrochemical Society Meeting, Washington DC, 1, 2002) Siripala WItem Growth and Characterization of Copper Indium Diselenide(Proceedings of the Technical Session of Institute of Physics, Sri Lanka, 1996) Chithrani, B.D.; de Silva, K.T.L.; Jayanetti, J.K.D.S.; Siripala, W.CuInSe2 thin films were prepared on Ti plates by electrodeposition from an aqueous solution containing CuCl2, InCl3 and SeO2. The deposition was carried out at -0.5V Vs SCE. X-ray diffraction and Scanning electron microscopy have been used to study the crystallographic and morphological properties of the samples. Effects of annealing in air have also been monitored. Apparent bulk structure changes have been observed during annealing. Annealing of films at 350 0C was found to result in the formation of CuInSe2 films having a chalcopyrite structure, indicating that the samples are of good quality.Item Observation of n-type Photoconductivty in Electrodeposited Copper Oxide Film Electrodes in a Photoelectrochemical cell(Solar Energy Materials, 1986) Siripala, W.; Jayakody, J.R.P.Copper oxide films were cathodically deposited on various metal substrates (Cu, Ti and Pt) using a basic solution of CuSO4, and it is found that they produce n-type photoconductivity in a photoelectrochemical cell. The photoresponse of these films is more pronounced than the previously known thermally grown p-Cu2O films, and the n-type behaviour could be converted to p-type by heating the samples in air. It is tentatively proposed that oxygen ion vacancies in the electrodeposited copper oxide films would result in n-Cu2O.Item Ammonium sulfide surface treatment of electrodeposited p-type cuprous oxide thin films(Electronic Materials Letters, 2014) Jayathileke, K.M.D.C.; Kapaklis, V.; Siripala, W.; Jayanetti, J.K.D.S.The effects of ammonium sulfide surface treatment on electrodeposited p-type polycrystalline cuprous oxide (Cu2O) thin films deposited on Ti substrates were studied. The structural and morphological properties of the films were investigated using scanning electron microscopy, x-ray diffraction, and energy-dispersive x-ray spectroscopy. The changes in the conductivities and photocurrents of the films after the ammonium sulfide treatment were determined. Films that had undergone the ammonium sulfide treatment showed reduced resistivities, enhanced spectral photoresponses, and enhanced current-voltage characteristics. The results showed that ammonium sulfide treatment improved the peak output current of the p-type Cu2O films by about 400% compared with those of bare Cu2O films. This improvement is attributed to the passivation of defects in the films by sulfur, showing that sulfur passivation provides a good method for improving of Cu2O-based devices.Item Sulfidation of electrodeposited microcrystalline/nanocrystalline cuprous oxide thin films for solar energy applications(Semiconductor Science and Technology, 2012) Jayathileke, K.M.D.C.; Kapaklis, V.; Siripala, W.; Jayanetti, J.K.D.S.Grain size of polycrystalline semiconductor thin films in solar cells is optimized to enhance the efficiency of solar cells. This paper reports results on an investigation carried out on electrodeposited n-type cuprous oxide (Cu2O) thin films on Ti substrates with small crystallites and sulfidation of them to produce a thin-film solar cell. During electrodeposition of Cu2O films, pH of an aqueous acetate bath was optimized to obtain films of grain size of about 100 nm, that were then used as templates to grow thicker n-type nanocrystalline Cu2O films. XRD and SEM analysis revealed that the films were of single phase and the substrates were well covered by the films. A junction of Cu2O/CuxS was formed by partially sulfiding the Cu2O films using an aqueous sodium sulfide solution. It was observed that the photovoltaic properties of nano Cu2O/CuxS heterojunction structures are better than micro Cu2O/CuxS heterojunction solar cells. Resulting Ti/nano Cu2O/CuxS/Au solar cell structure produced an energy conversion efficiency of 0.54%, Voc = 610 mV and Jsc = 3.4 mA cm?2, under AM 1.5 illumination. This is a significant improvement compared to the use of microcrystalline thin film Cu2O in the solar cell structure where the efficiency of the cell was limited to 0.11%. This improvement is attributed mainly to the increased film surface area associated with nanocrystalline Cu2O films.Item Study of Annealing Effects of Cuprous Oxide Grown by Electrodepostion Technique(Solar Energy Materials and Solar Cells, 1996) Siripala, W.; Perera, L.D.R.D.; de Silva, K.T.L.; Jayanetti, J.K.D.S.; Dharmadasa, I.M.Low temperature electrochemical deposition of cuprous oxide from aqueous solutions has been investigated. X-ray diffraction, scanning electron microscopy, optical absorption, and photo-response of liquid/cuprous oxide junctions have been used to study the deposits' crystallographic, morphological, optical, and electrical properties. Effects of annealing in air have been studied using the above mentioned methods. As-deposited cuprous oxide exhibits a direct band gap of 2.0 eV, and shows an n-type behaviour when used in an liquid/solid junction. Annealing below 300�C enhances the n-type photocurrent produced by the junction. Type conversion occurs after heat treatments in air at temperatures above 300�C. No apparent bulk structure changes have been observed during annealing below this temperature, but heat treatments above this temperature produce darker films containing cupric oxide and its complexes with water.Item 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.