Physics
Permanent URI for this collectionhttp://repository.kln.ac.lk/handle/123456789/3750
Browse
115 results
Search Results
Item Fabrication and characterization of electrodeposited nanocrystalline/microcrystalline cuprous oxide thin films(Proc. Annual Research Symposium, University of Kelaniya, 2008) Jayathilaka, K.M.D.S.; Wanninayake, W.T.M.A.P.K.; Siripala, W.; Jayanetti, J.K.D.S.The quest and need for clean and economical energy sources have increased interest in the development of solar energy applications. In particular, direct conversion of solar energy to electrical energy and chemical energy using semiconductor photoelectrodes has attracted attention for many decades. Among the various metal oxide materials for solar energy applications, a promising material is cuprous oxide (Cu2O) and is one of the oldest known semiconductors. It is low cost and non toxic and its component elements are readily available. It has a direct band gap of about 2 eV and a high optical absorption coefficient. Nanocrystalline thin films increase the effective surface area of the films as compared with the microcrystalline thin films. Therefore preparation of nanoparticles of Cu2O is of special importance to improve the solar energy conversion efficiency. In this study, Cu2O films were deposited electrochemically on Ti substrates. In this study, a simple electrochemical technique was developed to fabricate the Cu2O/CuxS heterojunction to be used in a thin film photovoltaic solar cell. Electrodeposited Cu2O thin films on Ti substrates were sulphided by directly applying an aqueous solution of Na2S on to Cu2O films and annealed at 200 0C for a few minutes. Then the samples were exposed to NH4S gas for a few seconds. It was observed that the photovoltaic properties and the diode characteristics of nano/micro/Cu2O/CuxS structures were better than that of micro/Cu2O/CuxS structures. The maximum conversion efficiency of the micro/Cu2O/CuxS cell was 0.12% (Voc= 240 mV, and Isc= 0.86 mA/cm2) and that of the nano/micro/Cu2O/CuxS cell was 0.28% (Voc= 420 mV, and Isc= 2.1 mA/cm2) under AM1.5 illumination.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 Eelctrodeposition of Nanocrystalline Cuprous Oxide Thin Films(Asian Conference on Solar Energy Materials and Solar Cells, 2006) Weerasinghe, W.J.L.D.; Siripala, W.; Jayanetti, J.K.D.S.Cuprous oxide is an attractive material for solar energy applications because it is low cost, non toxic and has a direct band gap of 2 eV. Electrodeposition for preparing cuprous oxide thin films is important because it provides the possibility of depositing n-type Cu2O thin films on conducting substrates, compared with p-type Cu2O films resulted in many other techniques. Electrodeposition of cuprous oxide is possible in a near neutral aqueous bath containing cupric ions and in a potential domain about 0 to 300 mV vs. SCE. Structural and morphological studies reveal that single phase polycrystalline films of crystalline size 1-2 ?m to 100nm of Cu2O can be electrodeposited by controlling the deposition parameters. It is revealed that for nanostructured film deposition low temperature deposition in galavanostatic mode is more suitable. Photoresponses of the films are very sensitive to the nature of the substrates. Particularly, n-type or p-type behavior of photoresponse is determined by the relative magnitudes of the photosignals produced by the photo electrodes. This is revealed by the spectral responses of the short and the long wavelengths of the illuminated light. The general photoresponse behavior is the same whether the electrode is in contact with an electrolyte or with a metal. This study reveals the possibility of electrodepositing nanocrystalline cuprous oxide thin films on conducting substrates. These films will be very useful in applications of solar energy converting devices.Item Optical and Structural Characrerization of Electrodeposited CuInSe2 thin films(Proceeding of the Technical Session of Institute of Physics, Sri Lanka, 2001) Seneviratne, L.P.; de Silva, K.T.L.; Siripala, W.; Rosa, S.R.D.; Sonnadara, D.U.J.CuInSe2 thin films were prepared on ITO coated glass substrates by electrodeposition from aqueous solution containing 0.005 M CuCl2 0.005 SeO2 and 0.01 M InCl3 at room temperature for a period of 30 minutes. To obtain better quality films, samples were annealed at different temperatures (200 0C, 350 0C and 500 0C) in Ar. XRD, optical absorption measurements, photovoltage measurements, spectral measurements and reflectance measurements were performed to characterize the films. According to the results, CuInSe2 is a p-type semiconductor. XRD shows three sharp CuInSe2 peaks of (112), (200) and (116) reflections for the samples annealed at 200 0C and 350 oC.Photovoltage of samples annealed at 400 0C and 500 0C were negligible (alomost zero). For the sample annealed at 200 0C, photovoltage was around 10 ? 15 mV. The highest photovoltage of around 150 mV was shown by the sample annealed at 350 0C. According to optical absorption measurements and reflectance measurements, the direct band gap was around 1.1 eV for both samples annealed at 200 0C and 350 0C. Only the sample annealed at 350 0C gave spectral responses.Item 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 Computational Study of I-V characteristics of ITO/Cu2 O/Metal junctions, Technical Session of Institute of Physics(Processing of the Technical Session of Institute of Physics, 1999) Wijesinghe, W.M.P.L.; Siripala, W.; Jayasuriya, K.D.; Kalingamudali, S.R.D.A theoretical model for current-voltage (I-V) characteristics of back-to-back diode systems was developed using the ideal diode equation. A computer model was developed using the language C++ to fit the experimental data to the theoretical equation and to determine the ideality factors and reverse saturation currents of each diode. This model was tested with commercial back-to-back diode systems. The values obtained for the above parameters from the theoretical fits were in very good agreement with the standard values. The experimental I-V characteristics data obtained for fabricated ITO/Cu2O/Metal (Au, Ag and Hg) structures were fitted to the model and values for the relevent parameters were obtained. These values indicate that the fabricated systems are back to back diodes except the ITO//Cu2O/Hg structure. Using this model, a good understanding of I-V characteristics of metal-semiconductor-metal diodes can be gained and thereby the quality of junction devices can be tested.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 Study of Daytime Variation of Convective and Non-Convective Zones in Salt Pan Solar Ponds(Annual Research Symposium, Faculty of Graduate Studies, University of Kelaniya, 2002) Perera, P.A.A.; Amarasekara, C.D.; Jayakody, J.R.P.; Punyasena, M.A.Item Construction and Filling of a Large-area Deep-tank Solar Pond for Harnessing Solar Energy(Annual Research Symposium, Faculty of Graduate Studies, University of Kelaniya, 2002) Jayakody, J.R.P.; Punyasena, M.A.; Perera, P.A.A.; Amarasekara, C.D.; Kumarasinghe, M.A.S.