Physics

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Author: search.filters.author.Wijesundera, R.P.End date: 2009

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    Characterisation of CuInS2 thin film prepared by electrodeposition and sulphurisation with photoluminescence spectroscopy
    (Solar Energy Materials and Solar Cells, 2003) Garuthara, R.; Wijesundera, R.P.; Siripala, W.
    Potentiostatic electrodeposition and sulfurization techniques were used to prepare polycrystalline CuInS2 thin films. X-ray diffraction and photoresponse measurements in a photoelectrochemical cell (PEC) revealed that photoactive polycrystalline CuInS2 films can be deposited on Ti substrate. Photoluminescence (PL) spectroscopy was used to investigate the prepared thin films and optically characterize them. PL spectra revealed the defect structure of the samples with an acceptor energy level at 109 meV above the valance band and a donor energy level at 71 meV below the conduction band. The CuInS2 thin films prepared in this investigation are observed to be In-rich material with n-type electrical conductivity.
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    ITO/n-Cu2O/p-CuxS Thin Film Solar Cell
    (Sri Lanka Association for the Advancement of Science, 1997) Perera, L.D.R.D.; Wijesundera, R.P.; Siripala, W.; Jayasuriya, K.D.; de Silva, K.T.L.; Jayanetti, J.K.D.S.
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    Ti/Cu2O photoelectrodes in photlectrolytic solar cells
    (proceedings of the Technical Session of Institute of Physics, Sri Lanka, 2003) Wijesundera, R.P.; Susantha, P.K.K.; Jayakody, J.R.P.; Siripala, W.
    Cuprous Oxide thin films deposited on Ti substrates were investigated as photoelectrodes in a photoelectrochemical cell. Electrodeposition was carried out in an electrochemical cell containing aqueous solutions of cupric acetate and sodium acetate.X-ray diffraction (XRD) and scanning electronmicrographs (SEM) confirmed that the films are polycrystaline Cu2O films. X-ray photoelectron spectroscopy (XPS) revealed that the films are pure CU2O and there are noanyother phases. The photoresponse of the films in a PEC produced a zero bias photocurrent (XBPC) with an n-type photoresponse. Comparing with the thermally grown Cu2O films, an enhanced spectral response in the long wavelength region could be obtained with electrodeposited Cu2O on Ti substrate. A charge separation mechanism at the Ti/Cu2O interface isproposed as the possible reason for the observed spectral response enhancement.
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    A Photoluminescence Study on CuInS2 Thin Films Prepared by the Sequential Deposition Technique
    (Annual Research Symposium -Faculty of Graduate Studies, University of Kelaniya, 2001) Wijesundera, R.P.; Siripala, W.
    Solar energy conversion to electrical energy using low cost solar cells contributes substantially for a solution to the present global energy crisis. In this respect, various semiconductor materials are being studied for possible applications in low cost solar cell devices. Copper Indium Di Sulphide (CuInS2) is very promising semiconductor material because of its electronic and optical properties, which are suitable for these applications. Low-cost semiconductor material growth techniques normally produce unwanted electronic states in the material producing undesired effects on the solar cell application. In this investigation, CuInS2 thin films prepared by the electrodeposition of Cu films followed by the In deposition were used to prepare Cu-In alloy. Cu-In alloy was suplherized in an H2S chamber to grow CuInS2 films. X-ray diffraction and optical characterizations suggest that the films are of good quality. The photoluminescence study at low temperature produced two peaks at 815nm and 880 nm. This result suggests the band to band transition and the sulfur vacancy transition. Our study reveals that there are no other defect electronic states in the band gap except the S vacancies, confirming the good quality of the material
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    A Study of CuInS2 Thin Films for Photovoltaic Applications
    (Proceedings of the Technical Session of Institute of Physics, 1999) Wijesundera, R.P.; Nadesalingam, M.P.; Siripala, W.; Jayasuriya, K.D.; Kalingamudali, S.R.D.; Jayanetti, J.K.D.S.; de Silva, K.T.L.
    Thin films of copper indium disulphide (CuInS2) on Ti Substrate were prepared by annealing potentiastatically electrodeposited Cu-In alloy in H2S gas at 5500 C. Films were characteristised by X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectral response in a polysulphide electrolyte. XRD measurements revealed the formation of the polysrystaline CuInS2 thin films and the abscence of any other phases. SEM showed the formation of crystallites having the size about 0.2 ?m. Variations of spectral response, open-circuit voltage (Voc) and short circuit current (Isc) with annealing in air have been studied. As deposited CuInS2 films exhibit a direct band gap of 1.5 eV, and shows n-type behaviour when used in a Photoelectrochemical (PEC) cell. Heat treatment shows a considerable enhancement of the photoresponse.
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    A study of Peltier effect in a thermoelectric couple of n-type cuprous oxide and p-type cuprous sulfide semiconductors
    (Proceedings of the Annual Reaserch symposium, 2003) Abeywarna, U.K.; Gunawardana, E.P.P.C.; Bopege, D.N.; Rajapakse, R.R.M.; Wijesundera, R.P.; Siripala, W.
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    Construction of a Near Ideal Nanoammeter
    (1998) Wijesundera, R.P.; Kalingamudali, S.R.D.; Jayasuriya, K.D.
    A near ideal ac/dc nanoammeter was constructed using two operational amplifiers (op-amp) and a voltmeter. Small currents were converted into a voltage by the first op-amp and this was amplified into a larger voltage by the second op-amp. The amplified voltage was measuredby the voltmeter. The constructed meter has 10 and 100 nA ranges for the dc current measurements and 100 nA range for the ac current measurements.All the ranges were calibrated using a digital picoammeter. As compared to commercially available nanoammeters with similar features this meter has higher advantages such as almost zero internal resistance and negligible operating bias current. The construction cost of the meter is very low compared to a commercial ac/dc nanoammeter.
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    Study of Sulphidation of Electrodeposited Cu2O Thin Films for Solar Cell Applications
    (1998) Siripala, W.; Wijesundera, R.P.; Perera, L.D.R.D.; Jayasuriya, K.D.
    Cuprous oxide (Cu20 ) layers were potentiostatically electrodeposited on glass/ITO substrates and then they were partially sulphided using Na2S and H2S. Resulting layers were used to fabricate ITO/n-Cu20/p-CuxS thin film solar cells. Spectral response measurements showed that the cell structure exhibits both n- and p-type behavior. Sulphidation of Cu20 does not produce CuxS thick layers adequate for efficient heterojunction solar cell, but improved the photovoltaic activity. The best device fabricated shows V? = 240 mV and Isc= 1.6mA/cm2 under AM 1 artificial illumination.
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    A Correlation between activation energy and light absorption of WO3 incorporated TiO2
    (2002) Dharmaratna, W.G.D.; Roshan, P.W.C.; Siripala, W.; Wijesundera, R.P.
    The variation of electrical conductivity properties and light absorption properties are studied in W 6+ incorporated Ti02, Both conductivity and light absorption depend on the percentage of W 6+ incorporated into the crystal matrix of Ti02. The activation energy decreased by a maximum of 30% as a result of doping and the lowest activation energy was measured when the dopant concentration was 0.2%. The light reflectance decrease with the dopant percentage, but not in a monotonically decreasing passion. The variation of light reflectance as a function of dopant concentration showed a minimum when the dopant concentration was 0.2%. Both features are quite important in improving the photocatalytic properties of Ti02.
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    Photoelectrolysis of water using double-semiconductor electrodes
    (2003) Wijesundera, R.P.; Siripala, W.
    Production of hydrogen by splitting water using solar energy is an attractive method to store solar energy as chemical energy. Semiconductor material cuprous oxide (Cu20) is a candidate material for this because it possesses important semiconducting properties suitable for application in photoelectrolysis of water. In this investigation it was studied the possibility of using n- and p-type Cu20 thin film electrodes as a double photoelectrode system in a photoelctrochemical cell. In this system enhanced electron - hole potential energy available for the photoelectrolysis process eliminates the bias requirement. Therefore enhancement of zero bias photocurrent (ZBPC) is expected as compared with a single photoelectrode. The n-type Cu20 thin films were grown by potentiostatic electrodeposition . The p-type films were grown by using a thermal growth technique. Photoelectrolysis with the double- photoelectrode system was investigated in a photoelectrocehmical cell containing 0.1M Sodium acetate solution. Chopped light current-voltage measurements and phase sensitive detection method to obtain spectral responses were employed in the investigation. It was observed that when the double electrodes were operated the ZBPC is enhanced by 450% . In other words, the requirement of an external bias could be minimized in the double-photoelctrode system. Spectral response measurements revealed that the n-type photosignal is possible in the entire band gap spectral range. This investigation demonstrates that the double-semiconductor photoelectrode system where minority carriers drive the complete photoelectrolysis process could be employed with the semiconductor Cu2O to develop a photoelecrtolytic solar cell.