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Item Effect of Concentration of Cd2+ on the Material Properties of CdTe Thin Films Electrodeposited via a Two Electrode Electrolytic Cell(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Wedisinghe, K.C.; Atapattu, H.Y.R.; de Silva, D.S.M.Cadmium telluride (CdTe) is a vital semiconductor material which can absorb most of the electromagnetic radiation of solar energy spectrum to yield more efficient solar cells. Among the thin film fabrication methods, electrodeposition is an emerging technique to produce good quality CdTe materials using either two or three electrode system. This study was performed using the two electrode electrolytic system to investigate the effect of Cd2+ concentration on the material properties of CdTe thin films to enhance its photovoltaic activities. Electrodepositions of CdTe were carried out in an aqueous electrolyte which was prepared utilizing analytical grade CdSO4 as the cadmium and TeO2 as the tellurium precursors. Fluorine doped tin oxide coated conducting glass (1×3 cm2) and high purity carbon electrode were used as the working (cathode) and counter electrodes (anode) respectively in the electrolytic cell used for the depositions. The concentration of TeO2 was maintained around 1 mmol/L throughout while varying the CdSO4 concentration from 1.00 mol/L to 1.50 mol/L. pH of the electrolyte was initially adjusted to 2.2 and depositions were carried out in the cathodic potential range of (1.33 - 1.37) V at 65 °C while stirring at continuous stirring rate of 60 rpm. The resulting electrodeposited CdTe layers were heat treated for 10 minutes at 400 °C in air and subsequently, their optical, electrical morphological and structural properties were studied using UV-visible spectrophotometry, photo-electrochemical cell, scanning electron microscopy and X-ray diffraction spectroscopy. As elucidated by the results, at the deposition potentials of 1.34 V and 1.35 V, the short circuit current and open circuit voltage values were increased with the increasing of concentration of Cd2+ from 1.00 mol/L to 1.25 mol/L while the band gap energy reached to its theoretical value of 1.50 eV.Item Effect of Thermal Annealing on Electrodeposited CdS and CdS/CdTe Heterojunction(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Atapattu, H.Y.R.; de Silva, D.S.M.; Pathiratne, K.A.S.At present CdS/CdTe based solar cells have a significant commercial impression due to its lowcost, scalability, manufacturability and simplicity. Nevertheless, it is essential to elevate the optoelectronic qualities of CdS and CdTe materials and the interface properties of CdS/CdTe heterojunction and ultimately the efficiency of the solar cells. In this regard thermal annealing is one of the key steps to be considered in order to enhance the material and heterojunction properties. Hence, in this study, the effect of thermal annealing on electrodeposited CdS and CdS/CdTe heterojunction was investigated. CdS and CdTe semiconductor layers were potentiostatically electrodeposited on bare fluorine doped tin oxide (FTO) glass substrates and FTO/CdS respectively using the typical three electrode electrolytic cell. For both layers, saturated calomel electrode and high purity (99%) graphite rod were used as reference and counter electrodes respectively. 0.10 mol/L CdCl2 and 0.01 mol/L Na2S2O3 were used as Cd and S precursors respectively to produce CdS thin films while 1.35 mol/L CdSO4 and 1.0 mmol/L TeO2 were used as Cd and Te precursors respectively for CdTe. CdS layers were grown at cathodic deposition potential of 660 mV at pH 1.6 and temperature of 55 °C. Afterwards, one set of electrodeposited CdS samples was conveyed for fabrication of CdS/CdTe heterojunction. CdTe layers were grown on CdS layers at cathodic deposition potential of 650 mV at pH 2.3 and temperature of 65 °C. Subsequently, thermal annealing was carried out for both CdS and CdS/CdTe at three different temperatures; 390, 400 and 410 °C, for each annealing three different time periods; 10, 15, 20 min were considered. After the process of annealing all the samples were inspected for their optical, electrical and morphological properties using the techniques of optical absorption spectroscopy, photoelectrochemical cell and scanning electron microscopy respectively. According to the results, the optimum annealing conditions which yielded good optoelectronic qualities for CdS and CdS/CdTe were found to be 400 °C, 15 min and 390 °C, 15 min respectively.