Browsing by Author "Silva, D. S. M. De"

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Fabrication of FTO/CBD-CdS/ED-CdTe/Cu/Au solar cells and boosting its performance by CdCl2 treatment
(Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Gajanayake, G. K. U. P.; Silva, D. S. M. De; Atapattu, H. Y. R.; Lakmal, A. A. I.
The thin film CdS/CdTe solar cells are promising cost-effective clean energy generating devices against the global energy crisis. Chemical bath deposition (CBD) and electrodeposition (ED) were recognized as being simple and low-cost techniques over a range of growth techniques available for development of CdS and CdTe thin films respectively. The use of aforesaid two techniques successively in fabrication of glass/FTO/CBD-CdS/ED-CdTe solar cells was not reported. This attempt is to do so and moreover, to assess the effect of CdCl2 treatment in performance enhancement of the device produced. In preparation of thin CBD-CdS layers on FTO glass substrate, a bath consisted of Cd(CH3COO)2 (0.033 mol/L), CS(NH2)2 (0.667 mol/L), CH3CO2NH4 (1.0 mol/L) and NH4OH (25%) was employed at 90 ℃. Annealed (375 ℃ for 30 min) CBD-CdS samples were subjected to CdTe deposition by ED system equipped with a three electrodes system. Herein, the CdS thin films were specifically developed enabling them to withstand in a highly acidic bath during the ED process. The ED bath used consisted of CdSO4 (1.0 mol/L) and TeO2 (1.0 mmol/L) at pH 2.3 and 65 ℃. The potential of -0.650 mV was maintained between the reference and working electrodes during each deposition (3 hrs). Samples were sprayed with CdCl2 solution (1.0 mol/L) for 2 s and then annealed (390 ℃ for 15 min). Back contacts (Cu/Au) were deposited on the CdCl2 treated glass/FTO/CBD-CdS/ED-CdTe devices by thermal evaporation. The devices were characterized under the illumination of AM 1.5 (100 mW/cm2). The efficiencies of the CdCl2 treated devices were found to be higher (6.23%) than untreated ones (2.66%). A significant variation in Jsc, Voc, and FF values was observed in CdCl2 treated devices (24.68 mA/cm2, 664 mV, and 38.0%) over untreated devices (14.95 mA/cm2, 531 mV, and 33.5%). The SEM analysis revealed remarkable increment in CdTe grain sizes (~140 nm to ~591 nm) with less grain boundaries in the CdTe sample upon CdCl2 treatment, thus leading to improved photovoltaic performance. This work demonstrated that CdS and CdTe can be synthesized using cost effective methods of CBD and ED respectively and, the FTO/CBD- CdS/ED-CdTe/Cu/Au device efficiency can be significantly improved by the CdCl2 treatment.
Surface modification of Leucaena leucocephala wood biochar using coconut vinegar
(Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Udawatta, M.; Silva, R. C. L. De; Silva, D. S. M. De
Over the last few decades biochar has emerged as a popular low cost adsorbent for water treatment due to its abundance and cost-effectiveness. Number of studies have reported the efficiency of strong acids such as nitric, sulfuric, hydrogen peroxide, etc. in activating biochar. However, as these chemicals are expensive, corrosive and difficult to be handled by unskilled personnel, use of these chemicals is limited to industrial activation processes. To provide a user friendly economical activation process, this study focused to evaluate the ability of natural coconut vinegar, in activating Leucaena leucocephala wood biochar. Coconut vinegar, a common food additive, is a 4 % acetic acid solution in water (4 g acetic acid/ 100 mL vinegar, pH 2.5). Leucaena leucocephala is a common, fast-growing tree with light wood and soft foliage. It is widely used for fuelwood. In this study, air dried Leucaena leucocephala wood pieces were allowed to burn in a domestic kiln (300 ºC, 2 hours) to produce biochar. The activation of biochar was done by soaking it in coconut vinegar for 24 hours followed by oven drying (120 ºC, 3 hours). After cooling it was washed with de-ionized water and further dried in oven at 80 ºC overnight. Fourier transform infrared spectra exhibited hydration of the C-O-C bridges of the biochar surface introducing new -OH groups and the possible introduction of carbonyl/ester/carboxylic functional groups to the biochar surface after the vinegar treatment. Recently, a positive correlation has been cited among the number of Chronic Kidney Disease of Unknown Etiology patients and the levels of ground-water hardness, in Sri Lanka. Hence, the efficiency of coconut vinegar activated Leucaena leucocephala biochar in reducing calcium ions from potable water was tested. Adsorption and desorption studies carried out using column tests showed a 1.7 fold increase of calcium ion adsorption capacity and a 7 fold increase of calcium ion retaining capacity after the vinegar treatment, with compared to the non-activated biochar. Calcium content in solutions was measured using flame photometry. Calcium adsorption capacities of non-activated biochar and activated biochar determined by column tests ranged from 3.10-3.82 mg/g and 5.27-6.68 mg/g respectively while calcium retaining capacities ranged from 0.16-0.22 mg/g and 1.28-1.4 mg/g respectively. Batch studies matched with both Langmuir (R2 = 0.9761) and Freundlich (R2 = 0.9785) isotherm models. Maximum adsorption, qm was calculated as 23.8 mg/g using Langmuir equation. This study concludes that Leucaena leucocephala biochar can be activated using coconut vinegar to be used as a safe and cost-effective adsorbent for calcium ion removal from potable water.