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Item Fabrication of CdS/CdTe Thin Film Solar Cells via the Technique of Electrodeposition(Development of Solar Power Generation and Energy Harvesting, 2018) Atapattu, H.Y.R.; De Silva, D.S.M.; Ojo, A.A.; Dharmadasa, I.M.This study focused on fabrication of CdS/CdTe solar cells using the technique of electrodeposition as it is simple, low cost and scalable method. Initially, CdS and CdTe materials were individually deposited on fluorine doped tin oxide (FTO) glass substrates and optimum growth conditions were obtained by analyzing their structural, compositional, electrical, optical and morphological properties using the techniques of X-ray diffraction, Energy Dispersive X-ray spectroscopy, photo-electrochemical cell study, optical absorption spectroscopy and scanning electron microscopy respectively. Thereafter, final device structure ofglass/FTO/CdS/CdTe/Au was fabricated using the optimum growth conditions obtained for the two materials, CdS and CdTe. Finally the current density-voltage characteristics of the devices were obtained to assess devices. The best device structure exhibited short circuit current density (L) of 24.4 mA cm- 2, open circuit voltage (V) of 681.9 mV, Fill Factor (FF) of 0.32 and conversion efficiency of 5.4 per cent.Item An investigation into the effect of rate of stirring of bath electrolyte on the properties of electrodeposited CdTe thin film semiconductors(2018) Atapattu, H.Y.R.; De Silva, D.S.M.; Pathirane, K.A.S.; Dharmadasa, I.M.Electrodeposition (ED) has been recognized as a low cost and scalable technique available for fabrication of CdS/CdTe solar cells. Photovoltaic activity of these electrodeposited semiconductor materials drastically depends on the ED growth parameters namely; electrodeposition potential, concentrations and ratios of concentrations of precursors used to prepare the bath electrolyte, pH of the electrolyte, deposition temperature and rate of stirring of the electrolyte, In order to grow thin films with good photovoltaic properties, it is essential to maintain these variables at their optimum ranges of values during electpcKlepositions. Hence, this study was conducted to investigate the dependence of the properties of electrodeposited CdTe thin film material on the rate of stirring of the bath electrolyte. The CdTe material was grown on glassfFTO (2 x3 cm2) and glassIFTO/CclS (2 x 3 cm2) surfaces in bath electrolytes containing 1.0 motIL Cd504 and 1.0 mmolit TeO, solutions at differ¬ent rates of stirring within the range of 0-350 rpm while keeping the values of pH of the electrolyte, deposition temperature and cathodic deposition potential with respect to the saturated calomel electrode at 2.3, 65 0and 650 mV respectively. After the heat treatment at 400 c'C in air atmosphere, the deposited samples with a good visual appearance were selected and evaluated based on their morphological, elemental, structural, optical and electrical properties in order to identify the optimum range of rate of stirring for electrodeposition of CdTe thin film semiconductors. Results revealed that, rates of stirring in the range of 60-85 rpm in a 100 mG volume of electrolyte containing the substrate and the counter electrodes in the center of the bath with a separation of 2.0 cm between them can ekctrodeposit CdTe layers exhibiting required levels of morphological, structural, optical and electrical properties on both glass/FTO and glasslFTO/CdS surfaces.Item Post deposition surface treatments to enhance the quality of polycrystalline CdTe thin films for photovoltaic applications(Nit teria1s Chemi stry and Physics 213 (201S) 4065113, 2018) Atapattu, H.Y.R.; De Silva, D.S.M.; Pathirane, K.A.S.Cadmium telluride (CdTe) is one of the topmost thin film polycrystalline materials used in the photo¬voltaics (PV) industry today and post deposition surface treatment has been a major step used in the production process for improving the photovoltaic quality of the CdTe material. In the present study, several post deposition surface treatment processes including CdCl2 treatment were carried out on CdTe material and the properties of the materials were then analyzed with the intension of gaining an un¬derstanding of the effect of the post deposition process on the material properties and identifying better post deposition treatment processes that can be used to improve the PV quality of the material. In this study, CdTe thin films were potentiostatically electrodeposited using the typical three electrode elec¬trolytic cell consisted of a saturated calomel reference electrode and a high purity graphite counter electrode. 3Cd504.8H20 and Te02 were used as the cadmium and the tellurium precursors respectively and CdTe layers were electrodeposited on fluorine doped tin oxide (ETD) glass substrates and glass/PTO/ CdS surfaces at pre-identified growth conditions namely; cathodic deposition potential of 650 mV, pH of 2.3 and temperature of 65'C. Subsequently, deposited samples were annealed in air with CdCl2 and thereafter, comparable samples of glass/FTO/CdTe and glass/FTO/CdS/CdTe were subjected to surface etching with diluted HCl (DH), Br2-CH3OH (BM), HNO3-H3PO4 (NP), K2Cr2D7-H2504 (DS) and K2Cr207- CH3OH (DM). Surface treated samples were then characterized for their electrical, optical, elemental, morphological and structural properties using photo-electrochemical cell measurements, optical ab¬sorption spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy and X-ray diffraction spectroscopy respectively. The study reveals that, post deposition surface treatments with BM and NP etchings enhance the material qualities of polycrystalline CdTe layers to be used for fabrication of PV devices.Item Influence of the type of conducting glass substrate on the properties of electrodeposited CdS and CdTe thin films(Journal of Materials Science: Materials in Electronics (2018) 29:12419-12428 https://doi.org/10.1007/s10854-018-9358-8, 2018) De Alwisl, A.C.S.; Atapattu, H.Y.R.; De Silva, D.S.M.Owing to the greater efficiency in energy conversion by absorbing energy in a wider range of the solar spectrum, thin film CdSICdTe solar cells have been popularized as a prominent application of photovoltaics and the technique of electrodeposi-tion (ED) is an ideal method available for producing both CdS and CdTe materials upon its outrivaled simplicity, low cost, scalability and manufacturability. Typically the quality of these deposited thin films depends on several growth parameters and amid them, the type of conducting glass substrate plays a crucial role. This study is focused on the influence of conduct-ing glass substrate on the properties of electrodeposited CdS and CdTe thin films. Two types of glass substrates coated with different transparent conducting oxide (TCO) layers namely; fluorine-doped tin oxide (FTO) and indium tin oxide (ITO) having different sheet resistances (FTO: 7 and 13 Disq and ITO: 7 and 15 Disq) were considered. CdS and CdTe materials were electrodeposited respectively on each of these types of TCO layers using a three electrode electrolytic system under a consistent set of growth parameters which has been pre-optimized with respect to FTO having sheet resistance of 7 afsq. The deposited CdS and CdTe thin layers were subsequently heat treated and characterized to understand their optical, electri-cal, morphological and structural properties. Accordingly, CdS and CdTe semiconductor materials deposited on glass+10 (7 .0./sq) substrates have exhibited better optoelectronic qualities and hence, endorse the requirement of individual growth parameter optimization for each type of TCO glass substrate for the production of good quality CdS and CdTe thin films in photovoltaic device fabrications.Item Evaluation of solution parameters for CdCl2 solutions to be used in post-deposition treatments of CdTe thin films in CdS/CdTe solar cells.(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Atapattu, H. Y. R.; Silva, D. S. M. D.; Pathiratne, K. A. S.Owing to its high absorption coefficient and the near ideal band gap, CdTe has become one of the topmost solar energy materials available for conversion of solar energy into electricity. It exhibits excellent power conversion efficiencies, when coupled with the CdS window material to form CdS/CdTe heterojunction solar cells. Further, CdCl2 treatment has been identified as one of the promising post-deposition treatments available for achieving drastic improvements in the performance of CdTe material. However, no extensive investigations have yet been carried out to identify suitable solution parameters for the CdCl2 solutions used in the post-deposition treatment process. Hence, the present study was designed to investigate the effect of concentration and pH of CdCl2 solutions used for post-deposition treatments of CdTe material grown on glass/FTO/CdS surfaces. In this study, CdTe layers were potentiostatically electrodeposited on glass/FTO/CdS substrates in electrolytic baths containing 1.0 mol/L CdSO4 and 1.0 mmol/L TeO2 at pH 2.3. A cathodic deposition potential of 650 mV with respect to saturated calomel electrode and temperature of 65 °C at a continuous stirring rate of 60 rpm were maintained through the deposition. At the end of electrodeposition process, all the glass/FTO/CdS/CdTe samples were rinsed in de-ionized water and dried under a high purity nitrogen gas stream and conveyed for the CdCl2 treatment followed by air annealing at 390 °C for 15 min. For CdCl2 treatment, three different CdCl2 concentrations (1.0, 0.5 and 0.1 mol/L) were used. For each concentration, three different pHs; as prepared (5.6, 6.3 and 7.1 for 1.0, 0.5 and 0.1 mol/L CdCl2 solutions respectively), 2.0 and 6.5 at 25 °C were selected. Hence, nine sets of samples with two replicates in each were subjected to the CdCl2 treatment. Once the treatment process was over, samples were inspected for their optical, electrical and morphological properties using the techniques of optical absorption spectroscopy, photo-electrochemical cell studies and scanning electron microscopy. The results revealed that, two solutions; one with 1.0 mol/L CdCl2 solution at pH of 5.6 and the other with 0.1 mol/L CdCl2 solution at pH of 2.0 can be effectively used for the post-deposition treatment of CdTe material for improving its properties and eventually to produce power efficient CdS/CdTe based solar cells with ~80 % efficiency improvement compared to the untreated devices.Item Electrodeposition of CdTe thin films using a two electrode system(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Wedisinghe, K.C.; Atapattu, H.Y.R.; de Silva, D.S.M.Cadmium telluride (CdTe) is a promising material for thin film solar cell applications due to its ideal band gap of ~1.5 eV which has the ability to absorb the maximum of the solar spectrum and higher conversion efficiency of sun light. Among the various deposition techniques available to produce CdTe semiconductor material in commercial quantities, electrodeposition has drawn more attention due to its simplicity, scalability and easy control of the material properties through growth parameters; applied potential, temperature, pH and the composition of the bath etc. Since the reference electrode could be a potential impurity source in the conventional three electrode electrolytic system, this study was mainly focused on the use of two electrode electrolytic system to determine suitable deposition potential and pH ranges for growth of CdTe thin film while avoiding the influence of impurities. The two electrode electrolytic cell consisted of, fluorine doped tin oxide coated glass substrate as the working electrode and 99.99% pure carbon electrode as counter electrode was used for the deposition of CdTe thin films. The electrolyte contained analytical grade reagents of 1.25 mol/L CdSO4 and 1.0 mmol/L TeO2 as cadmium and tellurium precursors respectively. Prior to electrodepositions, pH of the electrolytic baths were varied from 2.0 to 2.4 at 25 °C. While changing the cathodic deposition potentials in the range of (1.30 - 1.37) V, the CdTe depositions were carried out stirring the bath at 60 rpm and at the temperature of 65 °C. Following the heat treatment of the samples for 10 minutes at 400 °C in air, the characterization of CdTe thin films was carried out based on optical absorption, photo-electrochemical cell, X-ray diffraction and scanning electron microscopic studies. The results of the study indicate that, CdTe thin films can be successfully grown in the cathodic potential range of (1.34 -1.35) V and at a pH of 2.2 using two electrode electrolytic system.Item Electrodeposition of well-adhered CdTe thin films for solar cell applications(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Atapattu, H.Y.R.; de Silva, D.S.M.; Pathiratne, K.A.S.Among the second generation thin film photovoltaics, CdS/CdTe based solar cell device is one of the leading contenders for large scale commercialization. Since the CdTe is the crucial absorber material of the foregoing device, it is essential to maintain a well-adhered CdTe layer to obtain high photovoltaic activities. If not, loosened CdTe layers with numerous pinholes can reduce the electrical, optical, structural and morphological properties of the material and hence extinguish the entire activities of CdS/CdTe solar cells. In the present study, an electrodeposition procedure was developed to fabricate welladherent CdTe layers to the substrate using the typical three electrode electrolytic cell. A fluorine doped tin oxide conducting glass substrate (7Ω/sq.) with dimensions of (1×3) cm2 was used as the working electrode in the cell. A saturated calomel electrode and a high purity graphite rod served as reference and counter electrodes respectively. All the electrodepositions were carried out using an aqueous solution containing 1.0 mol/L CdSO4, 1.0 mmol/L TeO2 and 5.5 mmol/L CdCl2. Based on the cyclic voltammetry studies and the stoichiometry of the proposed chemical reaction which forms CdTe material, the possible cathodic deposition potential (CDP) and pH ranges were identified to be in the ranges of 550-710 mV and 1.4-2.4 respectively. Henceforth, CdTe layers were electrodeposited at above mentioned conditions at temperature of 65 °C and subsequently annealed in air at 400 °C for 10 min. Thereafter, by considering the physical appearance of deposited CdTe layers and their adhesiveness upon a high pressure N2 flow, the feasible values for CDP and pH were found to be in the ranges of 590-660 mV and 2.0-2.4 respectively. To further fine-tune the values for CDP and pH, a series of CdTe layers were deposited at above feasible growth conditions and inspected for their electrical, optical, structural and morphological properties using the methods of photo-electrochemical cell, optical absorption spectroscopy, X-ray diffraction and scanning electron microscopy respectively. Results revealed that, the optimum CDP is in the range of 620-660 mV and pH is in the range of 2.1-2.3 to exhibit good photovoltaic qualities.