Browsing by Author "Siripala, W."

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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 Cu2O/TiO2 heterojunction thin film cathode for photoelectrocatalysis
(Solar Energy Materials and Solar Cells, 2003) Siripala, W.; Ivanovskaya, A.; Jaramillo, T.F.; Baeck Sung-Hyeon; McFarland, E.W.
A thin film heterojunction photocathode was developed consisting of 100nm of n-type titanium dioxide (TiO2) cathode surface deposited on p-type cuprous oxide (Cu2O). The cuprous oxide was deposited electrochemically on Ti foil. A photocurrent of 0.7mA/cm2(at -1V bias) and an open circuit photovoltage of 460mV were obtained under an illumination of 700W/m2. The photoresponse as a function of pH demonstrated that the TiO2 film protected the Cu2O underlayer against corrosion. These results suggest that using a simple and inexpensive heterostucture configuration, the corrosion limitations of Cu2O alone may be overcome while maintaining a relatively high efficiency for photoelectrolysis.
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.
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.
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.
A Comparative Study: Sequential and Single-Step-Electrodeposited CZTS Thin Films
(Physica Status Solidi, 2022) Fernando, W. T. R. S.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.; Siripala, W.
CZTS (Cu2ZnSnS4) is a relatively new and promising semiconductor material suitable for photovoltaic applications due to its favorable optoelectronic properties. Of the many techniques available for growing these films, a comparative study on sequential and single-step electrodeposition methods to grow CZTS films is carried out in this investigation to explore the possibility of improving the quality of the films using the inexpensive electrodeposition technique. Mainly in both methods, potentiostatic electrodeposition technique is adopted for growing CZTS thin films. In both methods, growth conditions of the CZTS films are optimized after measuring the photoresponses in a photoelectrochemical (PEC) cell of the films that resulted at the end of each deposition step. The observed structural and optoelectronic properties of the films reveal that, in general, structurally good and photoactive CZTS films can be prepared using both methods. Moreover, photoresponse and Mott–Schottky measurements on CZTS films in a PEC reveal that CZTS films prepared using the single-step electrodeposition have better photoactive properties and improved doping densities. This important finding shows that when developing CZTS-based solar cells using the inexpensive electrodeposition technique, single-step electrodeposition is more advantageous.
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.
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.
Computational Study of I-V characteristics of ITO/Cu2/Metal junctions
(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.
Construction of Cu2O Thin Film based Light Detector
(Proc. 28th Technical Sess. of Institute of Physics, Sri Lanka, 2012) Kalubowila, K.D.R.N.; Jayathilaka, K.M.D.S.; Siripala, W.; Jayanetti, J.K.D.S.
Cu2O homojunction solar cell
(HETC Symposium, 2014) Gunawardena, L.K.A.D.D.S.; Wijesundera, R.P.; Siripala, W.
Cu2O Homojunction Solar Cells: Efficiency Enhancement with a High Short Circuit Current
(2024) Thejasiri, S. A. A. B.; Jayathilaka, K. M. D. C.; Kafi, F. S. B.; Kumara, L. S. R.; Seo, O.; Yasuno, S.; Sakata, O.; Siripala, W.; Wijesundera, R. P.
Cu2O homojunction solar cells were fabricated using potentiostatic electrodeposition technique. n-Cu2O thin films were grown in an acetate bath while p-Cu2O thin films were grown in a lactate bath. In the growth of n-Cu2O films, cupric acetate concentration, pH and temperature of the bath, deposition potential and duration (film thickness) and annealing temperature were investigated. In the growth of p-Cu2O on n-Cu2O, concentration of copper sulphate and lactic acid solutions, pH and temperature of the bath, deposition potential and duration were investigated. In addition, the procedure of sulfidation of p-Cu2O film surface using (NH4)2S vapor, before depositing Au front contact, was also optimized to enhance the photoactive performance. The structural, morphological and optoelectronic properties of the Cu2O films were investigated using scanning electron microscopy (SEMs), high energy X-ray diffraction (HEXRD), hard X-ray photoelectron spectroscopy (HAXPES), spectral response and current–voltage (J-V) measurements. The best Cu2O homojunction solar cell exhibited Voc = 460 mV, Jsc = 12.99 mA·cm−2, FF = 42% and η = 2.51%, under AM 1.5 illumination. Efficiency enhancement with the record high Jsc value for the Cu2O homojunction solar cell has mainly been due to the optimization of pH of the n-Cu2O deposition bath and lactic acid concentration of the p-Cu2O deposition bath.
Donor and Acceptor Density Variations in Electrodeposited Cuprous Oxide Thin Films
(2007) Jayathileke, K.M.D.C.; Siripala, W.; Jayanetti, J.K.D.S.
Cuprous oxide thin films were electrodeposited in a cupric acetate bath and resulting films were investigated in a photoelectrochemical cell for determining the intrinsic defects density variations. Depth profiles of the current carrier generation in the thin films were studied using the variation in the absorption depths of incident photons. Magnitudes and sign reversal of the photocurrents generated by the incident monochromatic light were used for this purpose. It was observed that by controlling the pH value of the deposition bath density of both Cu and O vacancies, which are responsible for acceptor and donor levels respectively, can be controlled and thereby it is possible to electrodeposit either n-type or p-type cuprous oxide thin films.
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.
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)