Browsing by Author "Seneviratne, V.A."

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    Effect of Seed Layer on Opto-Electronic Properties of CdS Thin Film
    (Uva Wellassa University of Sri Lanka, 2019) Kumarage, W.G.C.; Kumarasinghe, R.K.K.G.R.G.; Wijesundera, L.D.B.R.P.; Seneviratne, V.A.; Jayalath, C.P.; Dassanayake, B.S.
    Among different methods used to grow CdS films, chemical bath deposition (CBD) and electrochemical deposition (ED) are two of the most commonly used techniques. A novel method of growing chemical bath deposited CdS thin films (CBD-CdS) by using electrodeposited CdS (ED-CdS) as a seed layer is reported and compared with conventional ED-CdS and CBD-CdS films in this work. Conventional ED-CdS films were deposited for a duration of 60 min under potentiostatic conditions of -600 mV against the Ag/AgCl electrode at a bath temperature of 60 °C in a reaction solution of 0.05 mol dm-3 cadmium chloride, 0.05 mol dm-3 sodium thiosulfate and diluted H2SO4. Conventional CBD-CdS films were grown using 0.001 mol dm-3 cadmium sulfate, 0.002 mol dm-3 thiourea and 1.1 ml of ammonia solution for a period of 60 min. The seedassisted CBD-CdS films (ED/CBD-CdS) were grown by depositing CBD-CdS on top on an ED-CdS layer deposited for 3 min under the same conditions mentioned above. When compared, the ED/CBD-CdS system showed superior ISC (19.4 µA) performance in PEC cell (CdS/0.1 mol dm-3 Na2S2O3/Pt) compared to other two systems due to its homogeneity, enhanced majority carrier concentration, high surface roughness, and improved inter-particle connections. The ED/CBD-CdS system also showed a significant improvement in VOC (198 mV) over CBD-CdS (169 mV) and ED-CdS (168 mV) systems potentially due to higher flat band potential. Additionally, comparatively high Eg value of 2.45 eV was obtained for the ED/CBD-CdS due to lower disorder value of ED/CBD-CdS system. These results suggest that the novel method of CdS deposition, seed assisted CBD-CdS thin films demonstrate better opto-electronic properties compared to both EDCdS and CBD-CdS films alone.
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    Synthesis and characterization of sodium ion conducting solid polymer electrolytes based on poly (ethylene oxide)
    (Uva Wellassa University of Sri Lanka, 2015) Wanithunga, W.A.A.E.B.; Pitawala, H.M.J.C.; Seneviratne, V.A.
    Developments of novel ion conducting materials for energy storage devices are presently receiving much attention due to demand of energy. Among different strategies, polymer based solid electrolytes have several advantages such as light weight, flexibility and absence of leakage of electrolyte, compared to the conventional liquid electrolytes (Gray, F. M., 1991). In this work, synthesis of poly (ethylene oxide) (PEO) based sodium ion conducting electrolytes and characterization them using complex impedance spectroscopy, polarization microscopy, and FTIR spectroscopy are discussed. Methodology The polymer electrolytes were synthesized using common solvent casting method. Prior to use, PEO and salt (NaClO4) were vacuum dried at 50 °C and 120 °C respectively. Appropriate quantities of PEO and NaClO4 were mixed keeping the oxygen to Na molar ratios as n:1, where n=80, 60, 50, 40, 30, 20, and 15. Mixtures were dissolved in acetonitrile and stirred well for 24hrs at room temperature and the slurry was cast on a Teflon support. Prior to take measurements, the prepared electrolyte films were vacuum dried over 24 hrs. In order to study the temperature dependence of ionic conductivity, the complex impedance measurements were carried out. The surface morphology and polymer-salt interactions of some selected samples have been studied using polarization microscopy and FTIR spectroscopy respectively. Results and Discussion The temperature dependence of ionic conductivity for the solid polymer electrolytes (PEO)n NaClO4 (n=80, 60, 50, 40, 30, 20, and 15) is shown in Figure 01(A). It is clear from this figure that the electrolyte (PEO)20NaClO4 shows the highest ionic conductivity at room temperature(25 °C). The room temperature conductivity of the sample (PEO)20 NaClO4 is S cm . The plots of the variation of conductivity versus Na /PEO molar ratios at various temperatures (conductivity isotherms) is shown in Figure 01(B). These results also indicate the highest ionic conductivity for the sample (PEO)20NaClO4 for different temperatures. A closer inspection of the curves of Figure 01(A) reveals that the semi-crystalline to amorphous phase transition occurs around 60 °C and that a much greater conductivity enhancement occurs in the crystalline phase compared to that of amorphous phase. The crystalline to amorphous phase transition of the samples (PEO)nNaClO4 (n=80, 60, 50, 40, and 30) is much more visible compared to the samples of (PEO)15NaClO4 and (PEO)20NaClO4 and transition has almost disappeared for those two samples. This is revealed that the ionic conductivity of electrolytes (PEO)15NaClO4 and (PEO)20NaClO4, does not follow the Arrhenius type but Vogel-Tamman- Fulcher (VTF) behavior indicating their amorphous nature (Pitawala et al., 2007).