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Item Electrodeposited homojunction Cu2O solar cell on FTO substrate(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Kafi, F. S. B.; Jayathilaka, K. M. D. C.; Wijesundera, L. B. D. R. P.; Siripala, W.Cuprous oxide (Cu2O), an abundant photoactive semiconducting material has optimum optoelectronic properties to develop efficient, inexpensive and eco-friendly solar cells. Even though, it is possible to fabricate Cu2O based hetero or Schottky junction solar cells, it is believed that the reduction of interface strains via application of surface treatments can produce best efficient homojunction Cu2O solar cell. Apart from the homogeneity of a p-n junction, reduction of contact resistances of a solar cell also has a great impact on its overall performance. Previous studies have shown that, annealing and/or sulphidation of thin film Cu2O enhances the surface properties while sulphided p-Cu2O/Au junction exhibits ohmic behavior as well. Thus, in this study possibility of developing efficient thin film homojunction Cu2O solar cell on FTO substrate was tested by improving the surface properties of n- and p-Cu2O thin film layers. n-Cu2O thin film was potentiostatically electrodeposited in a three electrode photoelectrochemical cell, contained 0.1 M sodium acetate and 0.01 M cupric acetate, acetic acid at bath pH value of 6.1 and then, this thin film FTO/n-Cu2O photoelectrode was annealed at temperature of 4000C to form very thin p-Cu2O layer with lower surface defects. Subsequently, for a thicker absorber layer a thin film ptype Cu2O was electrodeposited on annealed FTO/n-Cu2O photoelectrode using a lactate bath, consisted 3 M lactic acid, 0.4 M copper(II) sulphate and 4 M sodium hydroxide at bath pH value of 13.0. Finally, to form ohmic back contact this bi-layer is directly exposed to ammonium sulphide vapor for 8s and sputtered thin film of Au on it. Photoresponses and modulated light induced current-voltage characterization of this final thin film Cu2O homojunction is given the highest VOC and JSC values of 154 mV and 3.905 mA/cm-2 respectively. This result revealed that application of surface treatments to the thin film n-Cu2O and the bi-layers ameliorates surface properties, thereby the optoelectronic properties. Parameterization of surface treatments and improvements in the front contact will further improve this homojunction solar cell.Item Optimization of growth parameters of photoactive Cu2ZnSnS4.(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Fernando, W. T. R. S.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.; Siripala, W.Cu2ZnSnS4 (CZTS) is a promising candidate for application in low-cost and environmentally friendly thin film solar cells due to its optoelectronics properties. It is a perfect absorber material for photovoltaic applications due to its high absorption coefficient (>10-4 cm-1) and direct optical band gap (1.4 - 1.5 eV). Among the CZTS preparation techniques, electrodeposition of Cu, Sn and Zn stack layers followed by sulphurisation in H2S is an attractive technique because of its simplicity, low cost and easy to control stoichiometry. In this investigation, optimization of growth parameters in order to obtain photoactive CZTS thin films by sulphurisation of electrodeposited Cu, Sn and Zn stack layers has been investigated. Cu thin film was electrodeposited on Mo substrate at –0.89 V Vs Ag/AgCl electrode 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 electrode 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. Deposition parameters of Cu, Sn and Zn have been obtained by voltammograms. In order to grow CZTS, Mo/Cu/Sn/Zn thin film electrodes were annealed at 550 oC for 60 min in H2S. Sulphurisation process was carried out at different temperatures and durations using set of identical Mo/Cu/Sn/Zn thin film electrodes and thereby optimized temperature and duration of the sulpurisation. Atomic ratios of initial Cu, Sn and Zn layers could be crucial parameters in determining properties of CZTS thin films. Therefore, atomic ratios of Cu/Sn/Zn layers were optimized by changing Cu, Sn and Zn deposition duration. Various combinations of deposition durations were carried out and optimized by monitoring the dark and light I-V measurements in a PEC containing 0.1 M sodium acetate. Dark and light I-V characteristics revealed that the best photoactive CZTS films can be grown by depositing Cu for 20 min, Sn for 10 sec and Zn for 10 sec. Results further showed that photoconductivity of CZTS thin films is p-type. It is evident from reflectance measurements that the band gap of the CZTS films is 1.5 eV. In conclusion, it is found that the highest photoactive p-CZTS thin films can be grown by sulphurisation of electrodeposited Cu, Sn and Zn stack layers on Mo substrate using H2S at 550 oC for 60 min. Cu: Sn: Zn ratios of the stack layers are the crucial parameters in determining photoactive CZTS thin films. The methodology developed in this study will be further investigated in order to develop the materials for wider applications.Item Improvement of p-Cu2O/Au interface by controlling the pH of the electrodeposition bath of Cu2O(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Kafi, F.S.B.; Jayathilekea, K.M.D.C.; Wijesundera, R.P.; Siripala, W.Metal-Semiconductor junction studies play a very important role in discovering new junction properties leading to improved electronic devices. Indeed, Schottky junction is among the fundamental structures used in modern optoelectronics and microwave devices. In this regard, low cost and eco-friendly metal-semiconductor devices with inexpensive materials and fabrication techniques are extremely important. Among other materials, p-Cu2O thin films grown by electrodeposition method have attracted as potential candidates for developing Cu2O based low cost Schottky junction devices. In this study, dependence of the p-Cu2O/Au junction properties on the pH of the Cu2O film deposition bath has been investigated for the development of low cost devices. p-Cu2O thin films were potentiostatically electrodeposited in a three electrode electrochemical cell containing 3M lactic acid, 0.4M CuSO4 and NaOH at different pH values. p-Cu2O/Au Schottky junctions were fabricated by sputtering Au on masked Cu2O samples. Dark Capacitance – Voltage measurements (Mott- Schottky plots) of the fabricated devices revealed that a positive shift of 620 mV of the flat band potential against Au for the change in pH of the film deposition bath from 7.0 to 13.0. This positive shift is significant when compared to the positive shift of 350 mV at the p-Cu2O/electrolyte interface observed earlier. The interaction of surface atoms with the electrolyte species at the Cu2O/electrolyte interface and the presence of bare surface atoms at the Cu2O/Au interface might have led to this improvement. The positive shift of the flat band potential manifests that the positive shift in the valence band edge of p-Cu2O relative to the Fermi level of Au increases the barrier height at the p-Cu2O/Au interface. Thus, the study reveals that the barrier height at the p-Cu2O/Au interface can be controlled with the pH of the film deposition both. As observed, dark Current-Voltage measurements on p-Cu2O/Au devices resulted nearly ohmic behavior for low pH values and non ohmic diode behavior for high pH values. This suggests that for high pH values of the film deposition bath of p-Cu2O improved Schottky junctions can be in fabricated with Au, suitable for various device applications such as rectifying circuits, photovoltaics, etc.Item Growth of CuZnS thin films by sequential electrodeposition and sulphurisation(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Fernando, W.T.R.S.; Jayathilekea, K.M.D.C.; Wijesundera, R.P.; Siripala, W.Copper Zinc Sulphide (CuZnS) is a promising new absorber material for solar cell applications. Indeed, this material is very attractive for low cost device applications due to abundance and low cost of the staring materials. Very recently, a CuZnS based solar cell with In2S3 window material has been reported having Voc of 0.41 V, Jsc of 10.6 mA/cm2, FF of 45% and of 1.94%. This initial finding has proven the possibility of developing this material as a solar energy material. Among the CuZnS preparation techniques, electrodeposition is an attractive technique because of its simplicity, low cost and possibility of making large area thin films. In this study, possibility of growth of CuZnS thin films by sulphurisation of electrodeposited Cu and Zn stack layers using S powder has been investigated. Cu thin film was electrodeposited on Ti substrate at –700 mV Vs Ag/AgCl for 15 min in an electrochemical cell containing 0.05 M sodium acetate and 0.005 M cupric acetate. Deposition of Zn thin film on Ti/Cu electrodes was carried out at -1.2 V Vs Ag/AgCl for 1 min in an electrochemical cell containing 0.2 M ZnSO4. Deposition parameters of Cu and Zn have been obtained by voltammograms. Set of identical Ti/Cu/Zn thin film electrodes having Cu/Zn ratio of 3.2 were prepared by maintaining the respective Cu and Zn thin film deposition durations for studying the sulphurisation process. In order to grow CuZnS, Ti/Cu/Zn thin film electrodes were annealed at different temperatures (400 oC, 450 oC, 500 oC, 550 oC and 600 oC) with different S contents (10 mg, 20 mg, 30 mg, 40 mg and 50 mg) for a duration of 60 min. CuZnS thin films were characterized using dark and light current voltage measurements in a PEC containing 0.1 M sodium acetate to obtain the best sulphurisation condition. Dark and light I-V characteristics revealed that the films annealed at 600 oC with the S content between 10 to 20 mg exhibits photoactivity. Further, photocurrent was always cathodic confirming the formation of p-CuZnS thin films. It was revealed in this preliminary investigation that the best photoactive films could be produced when films are annealed at 600 oC for 60 min in 20 mg S content. We have found, that photoactive p-CuZnS thin films can be grown by employing the technique of annealing electrodeposited Cu and Zn stack layers using S powder. Cu/Zn ratio of the stack layers could be the crucial parameter in determining the structure, conductivity type and resistivity of CuZnS films and therefore the methodology developed in this study could be further investigated, in order to develop the material for wider applications.Item 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.Item Sulphurisation of sequentially electrodeposited Cu-In alloy for the preparation of semiconductor thin films(2000) Wijesundera, R.P.; Siripala, W.; Jayasuriya, K.D.; Kalingamudali, S.R.D.Copper indium disulphide thin films were fabricated by suiphurisation of CuIn alloy prepared by a sequential electrodeposition method. Thin film layers of copper and indium were sequentially electrodeposited on a well-cleaned Ti substrate and on Ti/Cu thin film respectively. The Ti/Cu/In films were then heated at 130�C for 4 hours in air to form Cu-In alloy. Sulphurisation of Cu-In alloy was carried out at 550�C for 30 minutes in 1000/0 HzS gas with a constant flow rate. XRD measurement revealed that the chalcopyrite structure of single phase CulnS2 can be obtained by adopting a proper In concentration in Cu-In alloy. The photoresponse of the CulnS2 films in polysulphide showed the n-type behavior of the films. A p-type ZnSe thin film was deposited on CulnS2, by electrodeposition to produce Ti/CuInS2/ZnSe heterostructure. XRD measurement also revealed that the ZnSe films were amorphous. Spectral response of Ti/CulnS2/ZnSe structure in a PEC cell containing sodium acetate showed the photoactivity of both interfaces n-CulnS2/p-ZnSe and p-ZnSe electrolyte, This study reveals that the thin film solar cell structure Ti/CulnS2/ZnSe/metal may be developed to an efficient solar cell device. The solar cell parameters that we have observed so far are V? =330mV and Isc=2mA/cm2