Browsing by Author "Wijesundera, R.P."

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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.
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
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.
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.
An inexpensive universal serial bus interfaced home automation system
(IET Sri Lanka Network-19th Annual conference, 2012) Wijesundera, R.P.; Abeyratne, M.D.G.M.; Kalupahana, I.U.; Buddhika, W.A.P.; Kumara, S.D.; Jayatissa, N.W.K.; Harambearachchi, J.C.; Kalingamudali, S.R.D.
Biodegradable Plantain Pith for Galvanic Cells
(2012) Jayashantha, N.; Jayasuriya, K.D.; Wijesundera, R.P.
A number of locally available tubers/yams were studied as an electrolytic material for low cost environment friendly Galvanic cell. The cell was fabricated by sandwiching tissues made out of different types of tubers/yams slices between parallel Zn and Cu plates. A preliminary study revealed that cells made with plantain pith show comparatively better performance among the tested electrolytic materials. The performance of the cell was investigated by varying the separation between the electrodes and also by performing various treatments to the electrolytic material such as boiling and chopping after boiling. Best battery performance was obtained for chopped plantain pith after boiling. Stability of the battery fabricated with chopped plantain pith after boiling was tested by measuring the light intensity of a normal white LED with time. Results revealed that it is possible to light up LEDs for more than 500 hours provided the electrolyte is prevented from drying.
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.
Characterization of CuInS2 thin films prepared by electrodeposition and sulfurization 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.
Comparison of the properties of CZTS semiconductor films grown by sequential and single step electrodeposition techniques
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Fernando, W.T.R.S.; Jayathilaka, K.M.D.C.; Wijesundera, R.P.; Siripala, W.
Cu2ZnSnS4 (CZTS) is a promising semiconductor material suitable for application in low-cost and environmentally friendly thin film solar cells due to its superior optoelectronics properties. It is a perfect absorber material due to its high absorption coefficient (>10-4 cm-1 ) and direct optical bandgap (1.4-1.5 eV). Among the CZTS preparation techniques, electrodeposition is an attractive technique because of its simplicity, low cost and easy process controlling capability. In this investigation, a comparative study on CZTS films grown by two different techniques, namely, sequential electrodeposition and single step electrodeposition, has been carried out. Electrodeposition of Cu, Sn and Zn stack layers followed by sulphurisation with H2S is one of CZTS growth techniques. In this study, growth parameters of sequentially electrodeposited CZTS were optimized to obtain best photoactive CZTS thin films. Electrodeposition parameters of Cu, Sn and Zn have been obtained using voltammograms. Cu thin film was electrodeposited on Mo substrate at –0.89 V vs Ag/AgCl in an electrochemical cell containing 0.4 M CuSO4, 3 M lactic acid and NaOH at pH 11. Deposition of Sn thin film on Mo/Cu electrodes was carried out at -1.2 V vs Ag/AgCl in an electrochemical cell containing 0.055 M, 2.25 M NaOH and 8 ml of sorbitol. Zn thin film was electrodeposited on Mo/Cu/Sn at -1.2 V vs Ag/AgCl in an electrochemical cell containing 0.2 M ZnSO4. In order to grow CZTS, Mo/Cu/Sn/Zn thin films were annealed at 550 oC for 60 min in H2S. In the single step electrodeposition, CZTS thin films on Mo substrate were potentiostatically electrodeposited at -1.05 V vs Ag/AgCl for 40 min in a three electrode electrochemical cell containing 0.02 M copper (II) sulfate pentahydrate (CuSO4·5H2O), 0.01 M zinc sulfate heptahydrate (ZnSO4·7H2O), 0.02 M tin sulfate (SnSO4) and 0.02 M sodium thiosulfate (Na2S2O3) at room temperature. 0.2 M tri-sodium citrate (C6H5Na3O7) was used as the complexing agent and tartaric acid (C4H6O6) was used as the pH control solution. The pH of the bath was maintained at 5. The Ag/AgCl and platinum electrodes were used as the reference and the counter electrodes respectively. Then samples prepared were annealed at 550 oC for 30 min in H2S. CZTS films grown by two techniques were characterized using X-ray diffraction, reflectance, dark and light I-V, spectral response and C-V measurements in a PEC containing 0.1 M sodium acetate. Reflectance measurements reveal that the band gap energy of the films is 1.45 eV and I-V and spectral response measurements reveal that CZTS thin films were photoactive and p-type. The results obtained revealed that high quality photoactive CZTS can be prepared using both techniques. However, I-V and spectral response characteristics revealed that photoactive properties of CZTS thin films prepared by single step electrodeposition technique are superior in comparison to sequentially electrodeposited thin films.
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.
Correlation between glaze-colors and structural properties of the HIZEN celadons produced in the Edo period of Japan, by means of X-ray diffraction (?)
(Cer?mica, 2011) Hidaka, M.; Ohashi, K.; Wijesundera, R.P.; Kumara, L.S.R.; Watanabe, M.; Koga, K.; Choi Jae-Young; Sung, N.E.; Park, Y.J.
HIZEN celadons produced at Arita and Imari areas in Japan from 1630's to 1790's (Edo period) have been investigated by means of X-ray fluorescence analysis, and X-ray diffraction and X-ray absorption spectra using synchrotron radiation. It is found that, in the HIZEN celadons, the color brightness of the celadon glazes depends on the structural property of the raw basic ceramics taken at Imaizumi (Arita) and Ohkwachi (Imari), where the former is mainly Quartz-SiO2, and the later is Sanidine ((K,Na)Si3O8). It is confirmed that CaCO3 of natural wood ash added artificially into the raw celadon ceramics makes a glassy glaze on the surface of the basic body of the HIZEN celadons. Transition-metal ions (Cr, Cu, Zn) of very small amount are detected in the celadon glazes, in addition to Fe and Mn of small amount. It is considered that Cu and Cr are related to the color brightness of green-brown and blue-green in the HIZEN celadon glazes, respectively.
Correlation Between Local Structures and Partial Electronic Band States in Ferroelectric Bi4?Xlaxti3o12; 0.0?X?1.46
(Ceramics-Silik�ty, 2009) Hidaka, M.; Wijesundera, R.P.; Kumara, L.S.R.; Noguchi, Y.; Miyayama, M.; Choi Sun-Hee; Sung, N.E.; Kim, M.G.
The local structures and the partial band states near a Fermi level (EF) have been studied at room temperature in the ferroelectric phase of Bi4?XLaXTi3O12 (BLT) with 0.00?x?1.46 by means of X?ray absorption spectra (XAS) including EXAFS and XANES. The EXAFS spectra suggest that, as increasing the substituted La ions, the local structures around Ti and Bi ions in perovskite-blocks of (Bi2?XLaXTi3O10)-2 are gradually deformed till x=0.85, and are largely changed by a structural phase transition occurring between x=0.85 and 1.20. The XANES spectra suggest that there is a strong hybridization between Ti-3d(t2g) and O-2p bands and between Bi-6s and O-2p bands in the valence band states, while between Ti-3d(eg) and O-2p bands and Bi-6p and O-3s bands in the conduction band states. All of the XAS show interesting dependency on the concentration of the substituted La ions in BLT. The results suggest that, in BLT, a reducing spontaneous polarization induced by the La-substitution results from the deformation of the local structures around Ti and Bi ions and from modulation of the hybridized band states near EF.
Correlation between the green-like coloration and the structural and electronic properties of celadon glazes
(Cer�mica, 2012) Hidaka, M.; Takeuchi, K.; Wijesundera, R.P.; Kumara, L.S.R.; Watanabe, M.; Choi Jae-Young; Sung, N.E.
Correlation between the Izumiyama porcelain ceramics and the red-overglaze enamels of the Kakiemon-style porcelains
(Ceramics International, 2008) Kajihara, S.; Hidaka, M.; Wijesundera, R.P.; Kumara, L.S.R.; Kobayashi, H.; Koga, M.; Tsuru, T.; Koga, K.; Shimomura, K.; Choi Jae-Young; Sung, N.E.; Park, Y.J.
The Kakiemon-style porcelains made from 17th century at Arita are famous Japanese porcelains, characterized mainly by their colored underglaze and overglaze and by their original design of coloring spatial patterns in the porcelain surface. Raw materials of the red-overglaze enamels have been investigated by means of X-ray diffraction and X-ray absorption spectra using synchrotron radiations. It is found that Izumiyama porcelain ceramics of yellow color can produce the Kakiemon red-overglaze enamels by thermal treatment and water-washing, where Izumiyama is a collecting place of the raw porcelain ceramic at Arita. The brightness of the red-overglaze enamels is related on the local structure around Fe ions and the electronic band states of Fe ions near a Fermi level in ?-Fe2O3, in addition to the spatial density of the ?-Fe2O3 fine particles. The structural and electronic properties are slightly affected by an electron-hybridization between Fe ions of ?-Fe2O3 and oxygen ions of the (SiO2?Al2O3) complexes in the red overglaze.
Cu2O homojunction solar cell
(HETC Symposium, 2014) Gunawardena, L.K.A.D.D.S.; Wijesundera, R.P.; Siripala, W.
Design of an Inexpensive Digital Watt-hour Meter
(2003) Chandana, A.W.S.; Wijesundera, R.P.; Jayasuriya, K.D.; Kalingamudali, S.R.D.
An inexpensive digital watt-hour meter has been designed and tested using MCap 7 simulation package since commercially available digital watt-hour meters are very expensive. One of the major usages of watt-hour meters is to measure the power consumption of electricity consumers for billing purposes. Although digital watt-hour meters are commercially available,all electrical power supply companies through out the world including well-developed countries like the United States ofAmerica and the United Kingdom use analogue watt-hour meters to measure the power consumption. This is probably due the expensiveness ofdigital watt-hour meters. The designed digital watt-hour meter consists with analogue multiplier, analogue to digital converters, adder, registers, digital clocks, dividers, accumulators and digital displaying unit. Basically the current and voltage will be multiplied by using a four-quadrant analogue multiplier and then converted to digital signals using analogue to digital converters, which is clocked at a frequency significantly higher than mains frequency, to produce instantaneous values. The algebraic average of the output product per second will be the power consumption per second Finally, this will continuously be added and sent to the digital displaying unit to display watt-hour output. One of the major advantageous of the digital walthour meter is that the power consumption cannot be tampered like in analogue watt-hour meters where the power consumption can be very easily disturbed by changing the rotation power ofthe rotating disk.
Effect of pre-surface treatments on p-Cu2O/Au Schottky junctions
(Journal of the National Science Foundation of Sri Lanka,, 2021) Kafi, F.S.B.; Jayathilaka, K.M.D.C.; Wijesundera, R.P.; Siripala, W.
Cuprous oxide (Cu2O) is a suitable semiconducting material in fabrication for low-cost, eco-friendly semiconductor junction devices. Besides the parameterization of the growth conditions of Cu2O, formation of metal contacts impact the overall performance of these type of devices. The existence of unavoidable dangling bonds and/or dislocated surface atoms could lead to form imperfect contacts with metals, for example in Cu2O/Au junction devices. Nevertheless, modification of the Cu2O thin film surfaces prior to make contacts with Au has shown the capability to alter the junction properties. Here we report that, the application of surface treatments; annealing and/or sulphidation on specifically the electrodeposited p-Cu2O thin film surfaces, where p-Cu2O thin films were grown in low cupric ion concentrated acetate bath, has influenced the interfacial properties of particular p-Cu2O/Au Schottky junctions compared to the untreated p-Cu2O/Au Schottky junction. This has been well-established by the results of SEM and C-V characterizations of p-Cu2O/Au Schottky junctions. The subsequent annealing and sulphidation of p-Cu2O thin film surfaces have lowered the built-in potential value by 121 mV compared to the untreated Schottky junction. This result reveals the possibility of employing surface treatments on electrodeposited Cu2O thin films in fabrication of high efficient Cu2O based junction devices.
Effect of pre-surface treatments on p-Cu2O/Au Schottky junctions
(Journal of the National Science Foundation of Sri Lanka, 2021) Kafi, F.S.B.; Jayathilaka, K.M.D.C.; Wijesundera, R.P.; Siripala, W.
Cuprous oxide (Cu2O) is a suitable semiconducting material in fabrication for low-cost, eco-friendly semiconductor junction devices. Besides the parameterization of the growth conditions of Cu2O, formation of metal contacts impact the overall performance of these type of devices. The existence of unavoidable dangling bonds and/or dislocated surface atoms could lead to form imperfect contacts with metals, for example in Cu2O/Au junction devices. Nevertheless, modification of the Cu2O thin film surfaces prior to make contacts with Au has shown the capability to alter the junction properties. Here we report that, the application of surface treatments; annealing and/or sulphidation on specifically the electrodeposited p-Cu2O thin film surfaces, where p-Cu2O thin films were grown in low cupric ion concentrated acetate bath, has influenced the interfacial properties of particular p-Cu2O/Au Schottky junctions compared to the untreated p-Cu2O/Au Schottky junction. This has been well-established by the results of SEM and C-V characterizations of p-Cu2O/Au Schottky junctions. The subsequent annealing and sulphidation of p-Cu2O thin film surfaces have lowered the built-in potential value by 121 mV compared to the untreated Schottky junction. This result reveals the possibility of employing surface treatments on electrodeposited Cu2O thin films in fabrication of high efficient Cu2O based junction devices.
Effects of annealing on the properties and structure of electrodeposited semiconducting Cu?O thin films
(Physica Status Solidi (basic solid state physics), 2007) Wijesundera, R.P.; Hidaka, M.; Koga, K.; Sakai, M.; Siripala, W.; Choi Jae-Young; Sung, N.E.
The structures and the electronic states in electrodeposited semiconductor Cu?O thin films have been investigated for each annealing temperature (TA) by X-ray diffraction (XD) and X-ray absorption spectroscopy (XAS) near the Cu K edge using synchrotron radiation. The thin films prepared as grown and annealed at TA ? 175 �C, 200 �C ? TA ? 300 �C, TA = 400 �C are characterized mainly by the pure Cu2O-type structure, the pseudo-Cu2O-type having a superlattice structure, and two phases of Cu2O-type and CuO-type structures, respectively, while the film annealed at TA = 500 �C is single-phase CuO-type. The XAS spectra suggest that there is a structural phase transition occurring at about 400 �C, which induces a modulation of the local structure around Cu ions observed in the extended X-ray absorption fine structure (EXAFS) and the occupational electronic band states of Cu-4p localized just above the Fermi level, taken from X-ray absorption near edge structure (XANES). The open-circuit voltage suggests that the photosensitivity of the Cu?O thin films strongly depends on the annealing treatment and shows a crossover from an n-type to a p-type semiconductor. (? 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of Indium-Phosphide-Oxide on Photon Absorption of Multijunction Photovoltaic Cells
(2011) Abdulla-Al-Galib, M.; Barua, S.; Salam, K.M.A.; Wijesundera, R.P.
The objective of the anti-reflective coating on the solar cell has been to reduce the photon reflectance and increase the photon absorption. This increase in light trapping ability of the solar cell increases the maximum photocurrent of the incident solar spectrum. This increase of photon absorption of the cell increases the efficiency of the solar cell. In this paper we have worked on multi-junction solar cell and has shown how the photon absorption changes when we have an anti-reflective coating on top of the cell. The effect of using an anti-reflective coating on the photon absorption of multi-junction photovoltaic cell has been shown with simulation results. Our result shows that with the inclusion of an anti-reflective coating, Indium-Phosphide-Oxide, the photon absorption of the photovoltaic cell increases in the range of 528nm ? 710nm of solar spectrum over other current high efficient solar cell.