Browsing by Author "Wickramasinghe, G. C."

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Development of interdigitated electrodes on polyimide substrate using laser reduction of graphene oxide
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Wickramaarachchi, S. H.; Madurawala, K. H.; Wickramasinghe, G. C.; Jayasundara, D. R.; Weerawarne, D. L.
Graphene-based interdigitated electrodes (IDEs) provide a unique and chemically inert platform for various sensing applications. Fabricating such electrodes on flexible polymer substrates offers significant advantages over rigid electrodes due to their conformability and versatility. However, the process of coating graphene oxide (GO) and subsequently reducing it to reduced graphene oxide (rGO) on such heat-sensitive substrates presents substantial challenges. This study focuses on utilizing a laser reduction technique to transform GO coated on polyimide (PI) substrates into laser-reduced graphene oxide (L-rGO) using a 785 nm Cobalt continuous wave laser. This research aimed to optimize the laser reduction process to achieve minimal electrical resistance, enhancing the performance of the electrodes. The optimisation was conducted using a design of experiments (DoE) method, examining the effects of three key variables: laser power, scanning speed, and the number of scans. The optimal parameters were identified as a power of 500 mW, a scanning speed of 17.5 mm s-1, and 10 scans. Under these conditions, the resulting L-rGO lines exhibited a resistance of 4.4 ± 0.8 kΩ per centimetre, indicating an order of 105 reduction in resistance. The effective reduction of GO to rGO was confirmed through a combination of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). These characterization techniques provided detailed insights into the surface morphology and chemical changes occurring during the laser reduction process. The developed L-rGO IDEs were employed to detect sodium chloride (NaCl) in an aqueous solution using the electrochemical impedance spectroscopy (EIS) method. These IDE sensors showed excellent sensitivity and responsiveness to varying concentrations of NaCl, showing their potential for salinity sensing in water bodies. The optimised flexible rGO IDEs on PI substrates using a laser reduction technique, emphasise their scalability, cost-effectiveness, and suitability for advanced sensor technologies. This advancement opens new possibilities for the integration of flexible sensors in diverse fields, from environmental science to wearable technology, driving innovation in monitoring and detection systems.
Enhancement of dye sensitized solar cells by introduction of L-Ascorbic acid to the natural dye extraction of Carissa carandas fruit
(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Wickramasinghe, G. C.; Nupearachchi, C. N.; Perera, V. P. S.
Dye sensitized solar cells are categorized under third generation solar cells where a standard cell consists of nanocrystalline semiconductor photo anode which is very often titanium dioxide (TiO2), a dye sensitizer, a redox electrolyte and a counter electrode. Replacement of inorganic dye with natural organic dye as the sensitizer in these cells has gained both academic and commercial interest because it provides low cost, easy fabrication and non-toxic alternatives to inorganic dyes of dye sensitized solar cells. In this investigation, the dye extracted from Carissa carandas (Jamson) fruit was used as the dye sensitizer modified using L-ascorbic acid. The optical characteristics of dye and L-ascorbic acid were investigated separately by UV-visible spectroscopy. The maximum absorption wavelength of ascorbic acid was at 239 nm which is in the UV region and it was at 541nm in the visible region for the dye extraction. The TiO2 working electrodes were prepared by doctor blade method. Sintered TiO2 films were coated with extracted dye and L-ascorbic acid to explore the attachment of ascorbic acid molecules with dye molecules on the TiO2 photoanodes using three methods. The three methods of treatment of photo anodes with ascorbic acid were as follows; (1) TiO2 films were soaked in dye solution mixed with the ascorbic acid, (2) dye coated TiO2 films were soaked in L-ascorbic acid solution and (3) ascorbic acid coated TiO2 film were soaked in dye solution. The soaking time of TiO2 films in each solution was restricted to one hour. By varying the concentration of L-ascorbic acid in the solutions, series of cells were prepared to investigate the optimum concentration of ascorbic acid which gives the highest efficiency in each method. Platinum electrode was used as the counter electrode to assemble the dye sensitized solar cell and the space between photo anode and counter electrode was filled with a liquid electrolyte containing I-/I3- redox couple. Photovoltaic characterizations were done under 100mWcm-2 of light source. The highest efficiencies of dye sensitized solar cells for each three methods were 1.498%, 1.151% and 0.3078% at the optimum concentrations of ascorbic acid 0.14 M, 0.28M and 0.14M respectively. The observations support the idea of suppression of dye quenching by the ascorbic acid attached in between dye molecules to enhance the efficiency of the dye sensitized solar cells.