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Item Growth of photoactive Cu2ZnSnS4 by single step electrodeposition(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Fernando, W. T. R. S.; Jayathileka, 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 bandgap (1.4 - 1.5 eV). Among the CZTS preparation techniques, single step electrodeposition is an attractive because of its simplicity, low cost and easy to control stoichiometry. In this study, CZTS thin films on Mo substrate were potentiostatically electrodeposited 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:Na3-citrate) was used as complexing agent and tartaric acid (C4H6O6) was used as pH control solution. pH of the bath was maintained at 5.0 Ag/AgCl and platinum electrodes were used as reference and counter electrodes respectively. Mo substrate with a deposition area of 1×2 cm2 was used as the working electrode. Electrodeposition was carried out at -1.05 V vs Ag/AgCl using a Hokuto Denko model HZ-5000 Potentiostat/Galvanostat. CZTS samples were prepared using different deposition durations (5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 min). Optimum bath conditions were explored using cyclic voltammetry. Samples were characterized using XRD, optical absorption, dark and light I-V measurements and spectral response measurements in a PEC containing 0.1 M sodium acetate. XRD measurements evidenced that the formation of single phase polycrystalline CZTS. Reflectance measurements has revealed that the band gap energy of the films is 1.5 eV and I-V measurements revealed that CZTS thin films were photoactive and p-type. To enhance the photoactive properties films were annealed at different temperatures (500, 550, 6000C) and durations (15, 30, 45 min) in H2S surrounding. As the results, photoactive performance of the films enhance with the annealing treatment in H2S. In conclusion, it can be mentioned that the highest photoactive p-CZTS thin films can be grown by annealing the 40 min deposited samples at 5500C for 30 min in H2S. The methodology developed in this study will be further investigated, in order to develop the material for wider applications.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 Photoelectrolysis of water using electrodeposited Cu2O electrodes.(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Silva, A. G. T. D.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.; Siripala, W.At present, fossil fuels are the main energy contributor of the world’s energy needs but gradually depletion of fossil fuels is heading towards an energy crisis. Therefore it is very important for us to find out a renewable clean energy source to minimize the use of fossil fuels and environmental problems created by the burning fossil fuels. Among the suggested alternative fuels, hydrogen is one of the best and it can be produced by photoelectrolysis of water. Finding correct semiconducting materials and techniques are the key areas of research in the development of an efficient photoelectrolysis device. Ultra low cost electrodeposited cuprous oxide (Cu2O) is a good candidate material because it has required semiconductor properties for the process. p-Cu2O electrode electrolyte system requires external bias to produce photocurrent and this can be overcome by using n-Cu2O. However, in our previous studies, we have observed the possibility of enhancement of photocurrent at zero bias using double electrode system (electrodeposted n-Cu2O, thermally grown p-Cu2O, electrolyte system). In this investigation it was studied the possibility of photoelectrolysis of water using electrodeposited n- and p-Cu2O thin film electrodes as a double photoelectrode system in a 0.1 M sodium acetate photoelectrochemcal cell. n-Cu2O thin films on Ti substrates were potentiostatically electrodeposited at −200 mV Vs Ag/AgCl for 60 minutes in an aqueous solution containing 0.1 M sodium acetate and 0.01 M cupric acetate. The initial pH of the deposition bath was adjusted to 6.1. The temperature of the electrolyte was maintained at 55 °C and counter and reference electrodes were a platinum plate and a Ag/AgCl electrode, respectively. p-Cu2O thin films were electrodeposited on Ti substrate at -400 mV Vs Ag/AgCl for 40 min in a three-electrode electrochemical cell containing a 3 M sodium lactate and 0.4 M CuSO4 solution at pH 11. During the electrodeposition, the baths were continuously stirred using a magnetic stirrer. Prior to the film deposition, substrates were cleaned with detergent, dilute HCl, distilled water, and finally ultrasonicated in distilled water. Electrolytic solutions were prepared with distilled water and reagent-grade chemicals. n-Cu2O thin films are annealed at 150 oC for 10 min in air. Possibility of photoelectolysis using electrodeposited Cu2O has been investigated using dark and light current–voltage measurements in a three-electrode electrochemical cell containing 0.1 M aqueous sodium acetate solution. Results reveal that photoelectrolysis process is enhanced by 380% when n- and p-Cu2O double electrode system was operated compared to the n-Cu2O single electrode system.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.