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    Fermi‐level pinning and effect of deposition bath pH on the flat‐band potential of electrodeposited n‐Cu2O in an aqueous electrolyte
    (Wiley Online Library, 2016) Kafi, F.S.B.; Jayathileka, K.M.D.C.; Wijesundera, R.P.; Siripala, W.
    Capacitance–voltage (C–V) and modulated light-induced current–voltage measurements were employed to investigate the Cu2O/electrolyte junction of electrodeposited n-Cu2O thin films. The Mott–Schottky plots resulting from the C–V measurements revealed that the extrapolated flat-band potential of n-Cu2O films was strongly influenced by the pH of the bath where the films were grown. The flat-band potential change was 300 mV for a pH difference of 0.8 and showed that the surface chemistry at an n-Cu2O/aqueous electrolyte interface was strongly affected by the pH of the film deposition bath. In addition, current–potential measurements revealed that at the measured flat-band potential the photocurrent did not vanish for n-Cu2O films and the Fermi level at the interface was pinned due to the presence of electrically active surface states. Information on the presence of electrically active surface states and the shift in flat-band potential will be very useful for applications of n-Cu2O films in various devices.
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    Electrodeposited Cu2O homojunction solar cells: Fabrication of a cell of high short circuit photocurrent
    (Elsevier, 2016) Wijesundera, R.P.; Gunawardhana, L.K.A.D.D.S.; Siripala, W.
    A Cu2O homojunction solar cell was fabricated using a consecutive electrodeposition method of deposition of an n-Cu2O film followed by a p-Cu2O film, in two different acetate baths. Both n-type and p-type film growth conditions were optimized separately to yield high photocurrents in a photoelctrochemical (PEC) cell. Further, the resulted bi-layer films were investigated in the PEC for the verification of the formation of the p-n homojunction. In addition, p-Cu2O film surfaces of the bi-layers were sulphided using Na2S and (NH4)2S in order to improve the photoresponse of the homojunction before depositing a Au film for the solar cell device. The structural, morphological and optoelectronic properties of the Cu2O films were investigated using X-ray diffraction (XRD), scanning electron micrographs (SEMs), dark and light current–voltage (I-V) and spectral response measurements and observed that the films are of good quality. Incident photon to current efficiency (IPCE) and I-V characteristics of the solar cell device demonstrated that the Cu2O homojunction can produce a high short circuit current density Jsc. However, the overall conversion efficiency of the device is low due to poor fill factor and Voc. The solar cell characteristics of the structure Ti/n-Cu2O/p-Cu2O/Au were Voc=287.0±0.1 mV, Jsc=12.4±0. 1 mA/cm2, FF=25±2% and η=0.89±0.02%, under AM 1.5 illumination. The record high Jsc value of the device demonstrates the prospect being improved the efficiency of Cu2O homojunction solar cells by optimizing deposition, pretreatment and post treatment processes.
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    Electrodeposited nano-crystalline cuprous oxide thin films for solar energy applications
    (Annual Research Symposium, University of Kelaniya., 2012) 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 photo-electrochemical cell to determine the intrinsic defects density variations. 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. The study reveals that not only the pH value but also the cupric ion concentration of the acetate bath determines the nature of conductivity of the films. Structural and morphological studies revealed that nano-crystalline films of size, 100 nm, can be electrodeposited by controlling the deposition parameters. These films will be very useful in applications of solar energy converting devices.
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    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.
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    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.
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    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.
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    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.
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    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.
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    Methods for improving n-type photoconductivity Cu2O thin films
    (Semiconductor Science and Technology, 2014) Kalubowila, K.D.R.N.; Gunawardena, L.K.A.D.D.S.; Wijesundera, R.P.; Siripala, W.
    Electrodeposition technique is very useful for depositing n-type Cu2O thin films on various substrates. However, most of the reported n-type Cu2O thin film electrodes exhibit not only n-type photoactivity but also p-type photoactivity in photoelectrochemical cells. In this study, current?voltage characteristics and zero bias spectral response measurements were employed to investigate the possibilities to remove/minimize this unwanted p-type behaviour of n-type Cu2O thin films electrodeposited on Ti substrate. For this, prior deposition of Cu thin films on Ti substrate, low temperature annealing of Cu2O films in air and optimization of deposition bath pH were investigated. Growth of a very thin Cu film improved the n-type photosignal significantly and reduced the p-type photoresponse of the films. Films electrodeposited using an acetate bath of pH 6.1 produced only the n-type photoresponse. Low temperature annealing of Cu2O films in air improved the n-type photoresponse and it was found that annealing at 100 �C for 24 h produces the best result. These methods will be very useful to obtain electrodeposited Cu2O thin film with improved n-type photoactivity suitable for applications in thin film solar cells and other devices.
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    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.