IRSPAS 2016
Permanent URI for this collectionhttp://repository.kln.ac.lk/handle/123456789/15651
Browse
4 results
Search Results
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 Energy efficient hybrid water heating system(2016) Piyumal, P.L.A.K.; Nagahapitiya, N.W.H.G.B.; Jayatissa, N.W.K.; de Silva, D.S.M.As the world’s energy resources are diminishing, we need to find greener solutions through renewable energy sources that can generate electricity for heating, lighting homes and for a variety of commercial and industrial uses. Among many types of renewable energy resources, such as wind and solar energy, are constantly replenished and will never run out. At present we are experiencing an electrical energy shortage in Sri Lanka. However, we are still wasting so much of electrical energy in spite of the above crisis. The University of Kelaniya has many cafeterias. The cafeteria attached to the Gymnasium is the largest food and refreshments supplier in the university. The main refreshment for the students is hot tea. Hence, every day, every hour, the canteen has to produce a large number of cups of tea by using considerable amount of electrical energy for boiling water. Hence, the purpose of this project is to minimize the electricity consumption in the boiler using freely available sunlight. Initially, the project was focused to power the boiler using a photovoltaic array. Even though this method was straight forward, investigations have shown that this method was not financially viable. Hence, the next approach was to utilize solar thermal energy to heat the make-up water to the boiler which is significantly cheaper to implement than the previous. Fresh water is circulating through the heat exchanger unit placed on the top of the roof of the cafeteria. Heated water is fed to the boiler as make-up water. Although the heating system is unable to produce boiling water. It is capable of producing nearly half of the energy requirement for boiling the water. A temperature sensor was placed to measure the boiler temperature and the output of the sensor is fed to the heating element to maintain the boiler temperature at 373 K. According to the observation it is clear that make-up water temperature in the morning is 332 K which is little lower than the temperature of make-up water in the afternoon which is 342 K due to overnight cooling of the storage tank. Therefore, morning electricity consumption of the boiler is little larger than the evening. The average daily hot water consumption for making tea is approximately 78 liters in the morning and 88 liters in the afternoon. According to the calculations, it can be shown that the hybrid system is capable of saving 50% of electrical energy of the boiler. It can be concluded that the total energy provided by the solar heating system or the saving of the system is around 2450 kWh per annum.Item Surface characterization of chemically modified biochar derived from rice straw(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Irosha, K.P.C.; de Silva, D.S.M.; Rathnaweera, D.R.Biochar produced by decomposing variety of biomass feedstock is a carbon rich product that act as an efficient material for various applications such as contaminant management in soil and water, soil amendment in agriculture etc. Biochar obtained from biomass such as wood, manure and leaves have been studied worldwide for their adsorptive capacity, but reports on use of rice straw for such applications are limited. Hence the objective of the present study is to produce biochar using locally available rice straw. Samples of rice straw were chemically decomposed at 400 °C with H3PO4. In order to find a suitable surface modifier to increase the surface porosity and acidity, the resulted biochar materials were treated separately with oxidizing agents such as HNO3, KOH and H2O2. The pore size distribution of modified and the control samples were studied using scanning electron microscopy (SEM) technique. The functional groups available on biochar prior to and after chemical modifications were analyzed using the Fourier transform infrared spectroscopic (FTIR) technique. The FTIR spectral analyses disclosed significant increase in concentrations of the functional groups (carboxylic, alcoholic hydroxyl, phenolic hydroxyl and carbonyl) available on the surface of the KOH treated sample. The SEM analysis revealed about 40% increment in pore diameter of the rice straw biochar that was modified with KOH and H2O2 in contrast to non-modified biochar. Hence, according to the present study, the surface of the decomposed rice straw can be effectively modified with KOH to increase its surface porosity and functionality.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.