International Research Symposium on Pure and Applied Sciences (IRSPAS)

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Author: search.filters.author.Wijesundera, L. B. D. R. P.Has files: Yes

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    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.
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    Investigation of electrically insulating and thermally conductive materials for a Peltier module with n-Cu2O and p-Cu2O electrodeposited semiconductors.
    (International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Gajanayake, G. K. U. P.; Abeywarna, U. K.; Wijesundera, L. B. D. R. P.
    Thermoelectricity is a direct conversion of electrical energy into thermal energy and vice versa. Seebeck effect, Peltier effect and Thomson effect are thermoelectric effects observed for conductors during 1820-1920. After the development of semiconductors, a new era has begun in the field of thermoelectricity. Currently, the rare earth materials and their alloys are commonly used as semiconductors for constructing thermoelectric devices. In this research, copper based n-type Cu2O and p-type Cu2O semiconductors were used as thermoelectric materials. These semiconductors were deposited using potentiostatic electrodeposition technique in acetate bath. The study was carried out using two types of electrically insulating and thermally conductive material such as Thermal Heat Sink Transfer cooling pads (THST cooling pads) and mica. Multi stage Peltier modules were constructed using single stages assembling electrically in series and thermally in parallel. For the THST cooling pads, two stage Peltier module was assembled and a temperature gradient of 0.52 OC mm-1 at 2.0 V dc voltage was observed. However, the current through the module was higher and higher compared to the previous measurements when the data was repeated. It was found that the appearance of the semiconductor samples were changed when disassembling the module due to some fluid secreted from the THST cooling pads. The study was also done for both artificial and natural mica as electrically insulating and thermally conductive materials. For the artificial mica, a five stage Peltier module was built and it was observed 9.57 OC mm-1 temperature gradient for 2.0 V dc voltage. Having a three stage module of natural mica the temperature of the module decreases at the beginning and then increased while voltage was increased. A miniature temperature drop of 0.4 OC was able to achieve below the room temperature at 2.75-5.5 V range for the module with natural mica. In addition to that, a temperature gradient of 0.48 OC mm-1 was observed for this set up throughout the applied voltage. Present study demonstrated Peltier effect for both electrodeposited n-type Cu2O and p-type Cu2O semiconductors. The heating effect was always detected for the set ups with THST cooling pads and artificial mica as an insulating materials. However, the experimental data were not repeated for the semiconductor samples assembling with THST cooling pads due to some secretion of fluid. Therefore, THST cooling pads are not suitable for this kind of study. When considering artificial and natural mica as an insulating material, a higher temperature gradient was observed for artificial mica whereas a temperature drop was achieved using natural mica. Outcome of this study indicates that electrodeposited n-type and p-type Cu2O semiconductors along with mica as electrically insulating and thermally conductive materials can be used for a Peltier module.