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

Now showing 1 - 20 of 22

Activation of wood biochar and red brick using natural coconut vinegar
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Malka, U.K.M.; De Silva, R.C.L.; De Silva, D.S.M.; Chandrajith, R.
Number of studies have been carried out to determine the efficiency of strong oxidizers in activating natural raw materials used in low cost water purification processes. However, rural communities find it difficult to acquire most of such chemicals. Therefore, this study was aimed to determine the ability of natural coconut vinegar, which is a common domestic acidic solution, in activating abundantly available potential water purifying materials to reduce calcium (Ca2+) ions from water, further reducing the water hardness. In this study mature barks of Glyricidia (Glyricidia sepium), Gadumba (Trema orientalis) and Ipil Ipil (Leucaena leucocephala) were collected and air dried. These were carbonized (400-450 °C) in a closed vessel (2 hours) to produce biochar. Both biochar and brick particles in the range of 2.0-5.6 mm were selected for the analysis. For the activation these samples were soaked in natural coconut vinegar (biochar/brick: vinegar, 1:2 V/V) for 24 hours and completely dried in an oven (120 °C) for 3 hours. Laboratory scale glass columns (2 cm in diameter) were used to calculate Ca2+ adsorption and retaining capacities. Filtrates were analyzed for Ca2+ using flame photometer. Ca2+ adsorption and retaining capacities of each material were calculated per unit bulk volume of the material. Each test was duplicated, and the average was recorded. Untreated red brick and biochar of Glyricidia, Gadumba, Ipil Ipil showed Ca2+ adsorption capacities of 0.44, 0.30, 0.31, 0.27 mg cm3 and retaining capacities of 0.19, 0.01, 0.02, 0.02 mg cm-3 respectively. Activated red brick and biochar of Glyricidia, Gadumba and Ipil Ipil showed Ca2+ adsorption capacities of 0.76, 0.58, 0.68 and 0.63 mg cm-3 and retaining capacities of 0.25, 0.20, 0.23 and 0.15 mg cm-3 respectively. Increase in Ca2+ adsorption and retaining capacities were observed in all the materials tested after activation with vinegar. Further studies are continued to use the vinegar activated natural materials in a low-cost domestic drinking water purification process.
Catalytically induced pyrolysis of LDPE to liquid fuel
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Wickramaarachchi, W.A.A.S.; Premachandra, B.A.J.K.; De Silva, D.S.M.
Plastics are used in a wide range of applications because of their durability, lightweight, easy fabrication, and desired chemical and physical properties. Usually, plastic products are discarded after use to the environment as solid waste. Therefore, the low degradability of plastics and the high demand for plastic products have created a serious environmental issue. Recycling is one of the methods used in plastic waste management. As a recycling method, energy recycling or producing fuel oil from plastic waste has gained a promising interest. In this study, it was expected to convert selected used plastics to fuel oils through a pyrolysis process using a catalyst. A laboratory-scale pyrolysis system was developed and a low-cost conversation process for plastics to fuel oil was investigated in an environmentally friendly manner. Initially, virgin low-density polyethylene (LDPE) was used in this conversion as the control sample. Then waste wrapping materials made of LDPE were subjected to pyrolysis. A two-neck round bottom flask was used as the reactor while the heat was supplied by a LP gas burner. To control overheating and possible heat losses, the reactor was dipped in a soil bath during heating. A constant heating rate and a constant inert gas flow rate to the reactor were maintained throughout the experiment. The gases evolved by the pyrolysis were condensed. The distillate was collected while the uncondensed fraction was trapped first in a non-polar organic solvent and further in a basic aqueous solution to prevent possible hazardous emissions. A locally abundant mineral was tested as a possible catalyst for the pyrolysis to improve the quality of the resulting products. It was observed that the purity of the resulting fuel oil had been improved with the use of the catalyst. The resultant liquid fraction was conveyed for factional distillation and the fractions were characterized with GC-MS and FTIR techniques. According to the GC-MS analysis, the major constituents in the fraction obtained from virgin LDPE through uncatalyzed pyrolysis were decane, undecane and 1-tetradecene. The major constituents obtained through the catalytic pyrolysis of virgin LDPE were cyclopropane, 1- decene, undecane and pentadecane. The pyrolysis of waste LDPE resulted in cyclopentane, decane, undecane and 1-pentadecene as fractional distillates. The mineral tested as the catalyst has given significant improvement in the purity of the oil fractions produced. The combustion characteristics and viscosities of the resultant oils are to be determined and those will be compared with the commercially available fuel oils. The study will be extended for other plastic waste types including mixed waste.
Determination of selenium content in conventional leafy green vegetables consumed by Sri Lankans.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Dayarathna, A.G.S.; De Silva, D.S.M.
Selenium is an essential micro-nutrient for both humans and animals, specially incorporated in the form of amino acids. It is an important trace element required for humans for proper thyroid functioning and to promote their immune system. Most of the South Asian communities, especially Sri Lankans frequently have plant-derived food as the main component in their diet. Since it is widely believed that conventional leafy vegetables are a rich nutrient source, this study was carried out to determine the selenium content in seven selected types of abundant conventional leafy green vegetables that are consumed by Sri Lankans. Centella asiatica (Sin. Gotukola), Alternanthra sessilis (Sin. Mukunuwenna), Basella alba (Sin. Nivithi / Spinach), Boerhavia diffusa (Sin. Sarana), Ipomoea aquatica (Sin. Kankun), Amaranthus spinosus (Sin. Thampala) and Hygrophila schulli (Sin. Neeramulliya) are the leafy vegetable samples that were selected for the evaluation of selenium content. The samples were collected from five districts, (Gampaha, Kandy, Kurunegala, Anuradhapura and Puttalam) which have different environmental and climatic conditions. Soil samples corresponding to each leafy vegetable sample were also collected, and analyzed to identify the relationship between the selenium content in plants and soil. The sample analysis was carried out using Hydride Generation Atomic Absorption Spectrometer (HGAAS). Prior to the analysis, cleaned leafy vegetable samples and corresponding soil samples were subjected to acid digestion with nitric acid. Selenium concentrations in leafy vegetable samples analyzed were found to be in the range of 31.2 -103.2 μg kg-1 on dry weight basis. Centella asiatica (84.1 μg kg-1) and Hygrophila schulli (103.2 μg kg-1) varieties showed relatively high selenium concentrations, highest value of Selenium (103.2 μg kg-1) was reported from Hygrophila schulli and the lowest was from Boerhavia diffusa (31.2 μg kg-1). The selenium content in corresponding soil samples ranged from 96.4 to 133.9 μg kg-1 in dry weight basis. The measured soil selenium content was always higher than the corresponding plant selenium content; however the plants that were grown in selenium rich soils have not shown greater absorption of selenium. Hence, there may be no positive correlation between the uptake of selenium by leafy vegetables and the selenium content in soil.
Determination of selenium content in selected edible green leaves
(Ceylon Journal of Science, 2019) De Silva, D.S.M.; Dayarathna, A.G.S.
The selenium (Se) contents in seven conventional Edible Green Leaves (EGL) that consumed by Sri Lankans were determined using Hydride Generation Atomic Absorption Spectrometric method (HGAAS). The EGLs that were grown in five districts under different climatic conditions in Sri Lanka were collected from Gampaha, Kandy, Kurunegala, Anuradhapura and Puttalam areas. The EGL that were subjected to current study are Centella asiatica (Sin. Gotukola), Alternanthra sessilis (Sin. Mukunuwenna), Basella alba (Sin. Nivithi/ Spinach), Boerhavia diffusa (Sin. Sarana), Ipomoea aquatica (Sin. Kankun), Amaranthus spinosus (Sin. Thampala) and Hygrophila schulli (Sin. Neeramulliya). Soil samples corresponding to each EGL sample were also collected from Gampaha, Kandy and Anuradhapura districts in order identify a relationship between the Se content in plants and soils. Prior to the analysis EGL samples and corresponding soil samples were subjected to acid digestion with nitric acid. Se contents in the EGL were in the range of 31.2 – 103.2 μg kg-1on dry weight basis. According to the results, Centella asiatica and Hygrophila schulli varieties showed relatively higher Se content, while Hygrophila schulli shown the highest value and the lowest was reported in Boerhavia diffusa. The Se content in corresponding soil samples were ranged from 96.4 to 133.9 μg kg-1on dry weight basis. The Se content in soil was higher than that in plants, but there was no significant correlation between the Se content in soil and EGLs.
Development of ZnO Thin Films for Gas Sensing Applications
(International Research Conference (IRCUWU 2019),”Sustainable Business Transition through Technology and Innovation”, Uva Wellassa University of Badulla, Sri Lanka, 2019) Tharangika, M.O.; Atapattu, H.Y.R.; De Silva, D.S.M.
In recent decades' gas sensing technology has become significant due to its widespread and common applications in the areas of industrial production, automotive industry, medical applications, indoor air quality supervision and environmental studies. Currently, there is an increasing interest in finding nanostructured materials to develop high performance solid-state sensors for in-house and outdoor hazardous gas monitoring. Among the available gas sensing materials, metal oxide semiconductors typically maintain a leading role owing to their high sensitivity, low cost, small dimensions and simple integration. This study, focused on developing ZnO semiconductor thin films via the technique of electrodeposition followed by a heat treatment for detecting LP (Liquid Petroleum) and H2S gases. A three electrode electrolytic cell containing of 0.1 mol ZnSO4 was used to carry out the electrodepositions. A FTO glass substrate (1x3 cm2) was used as the working electrode against an Ag/AgC1 reference electrode while using a high purity carbon rod as the counter electrode. The Zn.electrodepositions were carried out in the cathodic deposition potential (CDP) range of 0.70-1.10 V and pH range of 4.0-1.0 at a temperature of 55 °C. Subsequently, samples were heat treated at 400 °C for 1 hour in order to form ZnO thin films and samples were then characterized for their crystalline structure, surface morphology and elemental composition using the techniques of X-ray diffraction spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy respectively. The sample grown at CDP of 0.80 V at pH of 1.5 for 20 minutes was found to have average sensitivity of 6% and 38% while exposing to LP and H2S gases respectively for 2 minutes at 30 °C. Further, it revealed that, the sensitivity of the ZnO material could be enhanced by controlling the electrodeposition and the heat treatment conditions applied for the formation of ZnO nanomaterials
Effect of CdTe nucleation layer on the performance of CdS/CdTe thin film solar cells
(J Mater Sci, 2023) Gajanayake, G.K.U.P.; Lakmal, A.A.I.; De Silva, D.S.M.; Dassanayake, B. S.
In this study, an electrodeposited CdTe nucleation layer (ED-CdTe*) was introduced on a chemical bath deposited (CBD) CdS layer prior to close-spaced sublimation (CSS) of the CdTe absorber layer to improve the efficiency of the CdS/CdTe solar cell by reducing the recombination mechanism in the depletion region. The ED-CdTe* nucleation layer grown in 40 s produced the highest efficiency of 9.12% with an open-circuit voltage (VOC) of 640 mV, while the CBD-CdS/CSS-CdTe solar cell delivered 8.07% efficiency, with a VOC of 596 mV. The ideality factor and the reverse saturate current density of the CBD-CdS/ED-CdTe*/CSS-CdTe solar cell were 2.28 and 6.65 × 10–5 mA/cm2, respectively. After being treated with CdCl2, the efficiency of the device with the nucleation layer (40 s) was elevated to 15.6% with a VOC of 761 mV, and that of the device with no nucleation layer was raised up to 14.6% with a VOC of 737 mV. Further, the solar cell with optimal ED-CdTe* nucleation layer showed the highest spectral response within the 400–900 nm wavelength range. The SEM and AFM analysis verified the formation of an ultrathin ED-CdTe* nucleation layer that can catalyse the film formation of CdTe by the CSS method while reducing the interface incongruity between CdS and CdTe layers.
THE EFFECT OF CONCENTRATION AND PH OF CdC12 SOLUTION USED IN CdC12 TREATMENT ON THE PROPERTIES OF CdS THIN FILMS
(Solar Asia 2018 Int. Conf. National Institute of Fundamental Studies, Kandy, Sri Lanka., 2018) Atapattu, I I.Y.R.; De Silva, D.S.M.; Pathiratne, K.A.S.; Dharmadasa, I.M.
Among the post deposition treatments available for development of CdS/CdTe solar cells, CdCl2 treatment has been identified as one of the key processing steps that can be effectively used for improving power conversion efficiency of the CdS/CdTe solar cell. This method was identified in late 1970s and currently is used for the CdS layers as well. The present study focuses on the effect of the concentration and pH of the CdCl2 solution used for the CdCl2 treatment on the quality of CdS layers based on their electrical, optical and morphological properties. In this study, CdS layers were potentiostatically electrodeposited on glass/FTO substrates at cathodic deposition potential of 660 mV verses a saturated calomel electrode at pH of 1.80 for 30 minutes in electrolytic baths containing 0.10 mol/L CdCl2 and 0.01 mol/L Na2S2O3. The temperature and the stirring rate of electrolytic baths were maintained constant at 55 °C and 60 rpm respectively. After the depositions, the samples were rinsed in de-ionized water and dried under a high purity N2 gas flow and conveyed for the CdCl2 treatment. Nine sets of samples with two replicates in each were treated separately with aqueous CdCl2 solutions having concentrations of 1.0, 0.5 and 0.1 mol/L and for each concentration three different pH values; as-prepared (5.60, 6.30 and 7.10 respectively), 2.00 and 6.50 were used. To perform the treatment, CdCl2 solutions were sprayed for 1 minute on the CdS layer until the layers were fully covered by the solution, allowed to dry and the samples were transferred for the process of annealing at 400 °C for 15 minutes in air. Subsequently, samples were rinsed in de-ionized water and dried under a high purity N2 gas flow. The electrical, optical and morphological properties of the CdS layers were then studied using photo-electrochemical cell measurements, UV-Vis absorption spectroscopy and scanning electron microscopy respectively. As results revealed, the CdCl2 solution with the concentration of 1.0 mol/L and the pH of 2.00 is suitable for achieving good material properties in the CdS layers.
EFFECT OF THE TYPE OF CONDUCTING GLASS SUBSTRATE ON ELECTRODEPOSITED CdS AND CdTe THIN FILMS
(Solar Asia 2018 Int. Conf. National Institute of Fundamental Studies, Kandy, Sri Lanka, 2018) De Alwis, A.C.S.; Atapattu, H.Y.R.; De Silva, D.S.M.
Thin film CdS/CdTe solar cells produced by the technique of electrodeposition (ED) on conducting glass substrates have become one of the leading applications of photovoltaics due to its high energy conversion efficiency via absorption of solar energy in a wider range within the solar spectrum. In previous studies, it has been established that the quality of CdS and CdTe thin films depends upon several growth parameters namely; the deposition potential, precursor concentrations & their ratios, pH of the electrolyte, deposition temperature and the rate of stirring of the electrolyte during the process of ED. In addition, the effect of conducting glass substrate on properties of the deposited material has been identified as a decisive consequence in achieving photoactive materials. Hence, the present study was carried out to determine the effect of the type of glass substrates on electrodeposited CdS and CdTe thin films. In this study, glass substrates coated with different transparent conducting oxide (TCO) layers namely; fluorine-doped tin oxide (FTO) and indium tin oxide (ITO) were considered and for each type of TCO layer two different sheet resistances (FTO: 7 vs. 13 Ω/sq and ITO: 7 vs. 15 Ω/sq) were taken into account. CdS thin layers were electrodeposited on these four types of glass substrates using an electrolyte consisted of CdCl2 (0.1 mol/L) and Na2S2O3 (0.01 mol/L) as Cd and S precursors respectively at pH of 1.7 and temperature of 55 °C for 30 minutes under cathodic deposition potential (CDP) of 650 mV vs. a saturated calomel electrode (SCE). Out of twelve replicates of CdS depositions on each type of glass substrate, six replicates from each type (glass/TCO/CdS) were conveyed for electrodeposition of CdTe thin films in an electrolyte consisted of CdSO4 (1.0 mol/L) and TeO2 (1.0 mmol/L) as Cd and Te precursors respectively at pH of 2.2 and temperature of 65 °C for 3 hours under CDP of 660 mV vs. SCE. The resulting CdS and CdTe thin films were heat treated at 400 °C for 10 minutes after each deposition and subsequent studies namely; UV-Vis absorption spectroscopy, photo-electrochemical cell analysis, scanning electron microscopy and X-ray diffraction spectroscopy were carried out to determine the optical, electrical, morphological and structural properties respectively of glass/TCO/CdS and glass/TCO/CdS/CdTe samples produced. As results revealed, the CdS and CdTe layers deposited on glass/FTO (7 Ω/sq) substrates have exhibited better optoelectronic qualities and the study further confirmed the dependence of material quality on type of the conducting glass substrate. Hence, the individual growth parameters optimization for each type of TCO glass substrate is an essential step in electrodeposition of good quality CdS and CdTe thin films for solar cell fabrications.
Effect of thermal annealing of CBD-CdS on the electrical properties of CBD-CdS/ED-CdTe solar cell
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Gajanayake, G.K.U.P.; De Silva, D.S.M.; Atapattu, H.Y.R.; Thivakarasarma, T.
Chemical bath deposition, Electrodeposition, Thermal annealing, CdS/CdTe solar cell Thermal annealing is one of the key steps to enhance the optoelectronic properties of the CdS/CdTe solar cells. In this study, the effects of annealing temperature and annealing time of chemical bath deposited (CBD) CdS on the electrical properties of CBD-CdS/electrodeposited (ED) CdTe solar cells were investigated. CBD-CdS layers were prepared using pre-optimized deposition conditions (90 ℃, 55 min) on fluorine doped tin oxide (FTO) glass substrates utilizing a bath consisted of 0.033 mol/L Cd(CH3COO)2, 0.667 mol/L CS(NH2)2 as cadmium and sulfur precursors, respectively and therein, 1 mol/L CH3CO2NH4 and 0.735 mol/L NH4OH were used for pH adjustment. Thereafter, a set of CBD-CdS samples prepared was annealed at different temperatures (350, 375 and 400 ℃) by varying the annealing time (10, 20, 30, and 40 min). Consequently, CdTe thin films were electrodeposited on annealed CBD-CdS substrates using an ED-bath consisted of 1.0 mol/L CdSO4 and 1.0 mmol/L TeO2 at pH of 2.3, temperature of 65 ℃, and potential of -650 mV against a saturated calomel electrode. The prepared glass/FTO/CBDCdS/ED-CdTe samples were air annealed (400 ℃, 20 min) and Cu/Au back contacts were deposited using thermal evaporation technique. The electrical properties of the CBD-CdS samples were investigated by photo-electrochemical cell (PEC) study at the CBD-CdS/electrolyte junction. As per the PEC analysis, CBD-CdS sample annealed at 375 ℃, 30 min has shown the highest short circuit current density (Jsc) of 21.5 μA/cm2 , while the sample annealed at 400 ℃, 10 min shown the highest open circuit voltage (Voc) of 499 mV. The electrical properties of the CBD-CdS/ED-CdTe/Cu/Au devices were investigated under AM 1.5 light source and therein, CBD-CdS sample annealed at 375 ℃, 30 min scored the highest Jsc (14.12 mA/cm2 ) and the one annealed at 400 ℃, 10 min displayed the highest Voc (616 mV). Also, the device annealed at 375 ℃, 30 min showed the lowest series resistance (205 Ω) while the one annealed at 400 ℃, 10 min demonstrated the highest shunt resistance (1401 Ω). Accordingly, the 375 ℃, 30 min and 400 ℃, 10 min were found to be the effective conditions for annealing CBD-CdS that can result in materials with better electrical properties for CBDCdS/ED-CdTe/Cu/Au device fabrication.
Electro-deposition of Cadmium Zinc Sulphide at High Cadmium Ion Concentration, Low Zinc Ion Concentration, High Temperature and Low pH
(Faculty of Graduate Studies, University of Kelaniya, 2015) Sarathchandra, K.A.D.M.S.; De Silva, D.S.M.; Pathiratne, K.A.S.
Thin films are nanoscale materials which are widely used for solar cells and other optoelectronic devices. Cd(1-x)ZnxS (cadmium zinc sulphide) is formed by incorporating zinc ions to CdS (cadmium sulphide). Cd(1-x)ZnxS is a n-type semiconductor material which has a wider band gap than that of n-type CdS. Therefore, Cd(1-x)ZnxS can be used as a window material when application required low absorption of light and n-type semiconductor properties. Cd(1-x)ZnxS has been electro-deposited by varying cadmium ion concentration, zinc ion concentration, pH, deposition temperature and deposition time. Results reported here were based on the depositions conditions; 0.1 mol dm-3 cadmium ion concentration, 0.01 mol dm-3 zinc concentration, 2.45 - 2.50 pH and 50 °C deposition temperature. Electro-deposition experiments were carried out by Gamry ―series G 300‖ potentiostat while, working electrode was fluorine doped tin oxide/glass substrate, reference electrode was Ag/AgCl electrode and counter electrode was a semi-spherical graphite rod. The deposition voltage was identified from the cyclic voltammograms and shapes of the deposition current vs time plots. Electrodeposition reported in here was carried out at under-deposition voltages. The best values for electro-deposition parameters; voltage, pH, temperature and time were identified by observing their influence on the band gap values of the thin films deposited and the open circuit voltages of photo-electrochemical cell consisting of 0.1 mol dm-3 sodium thiosulphate electrolyte and the thin film semiconductor. A band gap range of 2.5 eV – 2.6 eV was obtained for Cd(1-x)ZnxS layer which is higher than the band gap of CdS. The open circuit voltage varied from -48 mV to -190 mV during optimization of voltage, pH, temperature and time. An X-ray diffraction spectrum has shown that Cd(1-x)ZnxS layer has a single hexagonal crystal phase. The crystal parameter, a = 4.1264 Å and it was lower than the standard CdS (a = 4.1364 Å). The results indicate that Cd(1-x)ZnxS thin films can be produced under the given conditions as a window layer for thin film solar cells in order to harvest more light and hence to improve the efficiency.
Electrochemical conversion of graphite to graphene oxide: A preliminary study
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Gunarathna, M.D.; De Silva, D.S.M.
Graphene-based materials are two-dimensional atomic crystals composed of sp2 hybridized carbon atoms. The family includes graphene, graphene oxide (GO), reduced graphene oxide, and graphene quantum dots. Graphene is an allotrope of carbon with hexagonal lattice and it has gained immense attention in many industries due to its exceptional applications in electronics, water purification, adsorption studies, etc. Many recent studies proposed different routes of GO synthesis. This study reports an electrochemical conversion of locally available raw graphite obtained from Bogalapathala to GO. Electrochemical conversion of graphite to graphene has great potential in the production of graphene oxide and it has gained the attention of the scientific community due to its easiness and environmentally friendly practices. The significance of the electrochemical conversion process is the minimal chemicals requirement compared to other methods developed. The local graphite powder was compressed into pellets using a pellet maker designed by the researcher with a cavity to accommodate the Pt electrode. The graphite pellet was tightly wrapped with a permeable cellulose membrane to avoid loosening of the pellet during electrochemical process. The electrochemical cell consisted of a Pt rod as the working electrode and a carbon rod is as the counter electrode. These electrodes were immersed in an (NH4)2SO4 solution and a constant potential of 10 V was applied for 2 hours. The resulted product was dissolved in deionized water and centrifuged to collect the supernatant. The supernatant was heated at 90 °C under atmospheric pressure on a hot plate to evaporate the water and the residue was characterized using FTIR, UV visible spectrophotometry, and X-ray diffraction techniques. The UV and FTIR absorption spectra and the X-ray diffraction patterns confirmed the partial transformation of graphite to GO while the maximum yield of GO obtained after the evaporation was 1% (based on the mass of graphite powder used) and further investigations need to be performed to increase the yield.
Electrodeposited ZnS Thin Films for NO2 Gas Sensing Applications
(19th Conference on Postgraduate Research, International Postgraduate Research Conference 2018, Faculty of Graduate Studies,University of Kelaniya, Sri Lanka, 2018) Wickramathilaka, P.A.K.Y.; Namawardana, D.G.K.K.; Atapattu, H.Y.R; De Silva, D.S.M.
Sensors are becoming a consequential part in human’s daily life. Typically, they are classified based on the physical parameter sensed itself namely; thermal, mechanical, magnetic, chemical, and optical. Gas sensors are chemical sensors that can be fabricated as metal-oxide or metal-sulfide semiconductor materials viz.; TiO2, ZnO, CdS and ZnS etc. Among these materials ZnS is a highly abundant and non-toxic material and can be easily adopted for gas sensing applications. Electrodeposition can be identified as an ideal fabrication method owing to its simplicity and low cost in production amid various fabrication methods that have been employed for developing ZnS thin films. This study focuses on the growth of ZnS thin films for gas sensing applications using the technique of electrodeposition. A three electrode electrolytic system consists of an Ag/AgCl reference electrode, FTO glass substrate (1×3 cm2) working electrode and high purity carbon counter electrode was used in electrodepositing ZnS material in an aqueous electrolyte containing ZnCl2 (0.10 - 0.05 mol/L) and Na2S2O3 (0.01 - 0.05 mol/L) precursors. The ZnS depositions were carried out in the cathodic deposition potential (CDP) range of 0.70 - 1.10 V and pH range of 4.0 - 3.5 at temperature of 30 °C for 90 minutes. After deposition, samples were annealed at 300 °C for 10 minutes and characterized for their crystalline structure, surface morphology and elemental composition using the techniques of X-ray diffraction spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy respectively. The sample grown at CDP of 1.05 V at pH of 3.7 were found to have notable material properties and shown 2 Ω average change in resistance with respect to the initial average resistance of 26.2 Ω while exposing to NO2 gas at 3× 104 Pa and 30 °C within a time interval of 2-3 minutes
Electrodeposition and characterization of ZnO thin films for gas sensing
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Rathnaweera, U.M.C.; De Silva, D.S.M.; Atapattu, H.Y.R.
The gas sensor is a sensing device that measures target gas molecules in a given atmosphere specially in the monitoring of environmental contaminants in air, water, and soil. Sensors based on semiconducting metal oxides are being widely used for gas or vapour sensing owing to their properties such as non-toxicity, biocompatibility, compact device structure, high sensitivity and stability and ease of syntheses. The most popular semiconducting metal oxides-based gas sensing materials are ZnO, SnO2, WO3 and TiO2. Among them, ZnO is attracted more due to its other properties such as chemical and photochemical stability and high-electron mobility. Hence, ZnO is one of the most propitious materials in developing sensors in electronic and optical technologies. In this study, characterization and fabrication of ZnO for gas sensing applications using a simple and cost-effective electrodeposition method is discussed. Aqueous electrolytic solutions of Zn (NO3)2 and ZnSO4 were used as the Zn precursors to find the best suited precursor to electrodeposit ZnO. The deposition was performed under a three-electrode electrochemical cell consisted of FTO coated glass (1×3 cm2 , 7 Ω/m2 ), graphite rod (99.995%) and a saturated Ag/AgCl electrode as the working, counter, and reference electrodes respectively. The gas sensing ability of the ZnO films, developed under different deposition parameters (cathodic deposition potential, pH of the electrolyte, precursor concentration), was studied. By obtaining the workable cathodic deposition potentials (CDP) by cyclic voltammetry, the k best suited bath pH and the temperature to develop uniform ZnO thin films were found to be 3.5 - 4.5 and 55 ℃ respectively. Subsequently, the heat treated (425 ℃ for 1 hour) samples were characterized with UV/Vis spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray techniques to investigate the bandgap energy, crystal structure, surface morphology and the material’s composition respectively. The band gap energy of the material grown was fallen within 3.00 – 3.30 eV, while the crystals were found to be preferably grown along the [101] or [002] planes possessing hexagonal wurtzite structure in samples grown using two Zn precursors. SEM micrographs evidenced compact morphology with coral/rod-shaped appearance. According to the EDX analysis, Zn:O atomic ratio was revealed to be 1:1. The gas sensing ability of deposited films was examined against NO2 and H2S gases that causes due to electronic interactions between the crystallographic plane and the subjected gas molecules. The samples grown in 0.10 mol/L ZnSO4 at CDP 1.00 V in pH 4.50 at 55 ℃ was found to have an average sensitivity of 5% and 11% while the samples grown in 0.10 mol /L Zn (NO3)2 at CDP 1.10 V in pH 3.70 at 55 ℃ were found to have an average sensitivity of 2% and 5% after exposing to NO2 and H2S gases respectively for 5 minutes at 30 ℃.
Fabrication of CdS/CdTe Thin Film Solar Cells via the Technique of Electrodeposition
(Development of Solar Power Generation and Energy Harvesting, 2018) Atapattu, H.Y.R.; De Silva, D.S.M.; Ojo, A.A.; Dharmadasa, I.M.
This study focused on fabrication of CdS/CdTe solar cells using the technique of electrodeposition as it is simple, low cost and scalable method. Initially, CdS and CdTe materials were individually deposited on fluorine doped tin oxide (FTO) glass substrates and optimum growth conditions were obtained by analyzing their structural, compositional, electrical, optical and morphological properties using the techniques of X-ray diffraction, Energy Dispersive X-ray spectroscopy, photo-electrochemical cell study, optical absorption spectroscopy and scanning electron microscopy respectively. Thereafter, final device structure ofglass/FTO/CdS/CdTe/Au was fabricated using the optimum growth conditions obtained for the two materials, CdS and CdTe. Finally the current density-voltage characteristics of the devices were obtained to assess devices. The best device structure exhibited short circuit current density (L) of 24.4 mA cm- 2, open circuit voltage (V) of 681.9 mV, Fill Factor (FF) of 0.32 and conversion efficiency of 5.4 per cent.
Influence of the type of conducting glass substrate on the properties of electrodeposited CdS and CdTe thin films
(Journal of Materials Science: Materials in Electronics (2018) 29:12419-12428 https://doi.org/10.1007/s10854-018-9358-8, 2018) De Alwisl, A.C.S.; Atapattu, H.Y.R.; De Silva, D.S.M.
Owing to the greater efficiency in energy conversion by absorbing energy in a wider range of the solar spectrum, thin film CdSICdTe solar cells have been popularized as a prominent application of photovoltaics and the technique of electrodeposi-tion (ED) is an ideal method available for producing both CdS and CdTe materials upon its outrivaled simplicity, low cost, scalability and manufacturability. Typically the quality of these deposited thin films depends on several growth parameters and amid them, the type of conducting glass substrate plays a crucial role. This study is focused on the influence of conduct-ing glass substrate on the properties of electrodeposited CdS and CdTe thin films. Two types of glass substrates coated with different transparent conducting oxide (TCO) layers namely; fluorine-doped tin oxide (FTO) and indium tin oxide (ITO) having different sheet resistances (FTO: 7 and 13 Disq and ITO: 7 and 15 Disq) were considered. CdS and CdTe materials were electrodeposited respectively on each of these types of TCO layers using a three electrode electrolytic system under a consistent set of growth parameters which has been pre-optimized with respect to FTO having sheet resistance of 7 afsq. The deposited CdS and CdTe thin layers were subsequently heat treated and characterized to understand their optical, electri-cal, morphological and structural properties. Accordingly, CdS and CdTe semiconductor materials deposited on glass+10 (7 .0./sq) substrates have exhibited better optoelectronic qualities and hence, endorse the requirement of individual growth parameter optimization for each type of TCO glass substrate for the production of good quality CdS and CdTe thin films in photovoltaic device fabrications.
Influence of ZnS buffer layer on CdS/CdTe based solar cells
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Madhuwanthi, H.M.L.U.,; Mahanama, G.D.K.; De Silva, D.S.M.
Among thin film materials, cadmium sulfide (CdS) is the best suited window material as a heterojunction partner in cadmium telluride (CdTe) based solar cells due to its wide and direct band gap. In order to enhance the solar cell efficiency, a buffer layer such as zinc sulfide (ZnS) having a relatively wider band gap can be introduced into the conventional CdS/CdTe heterojunction solar cell by reducing the thickness of CdS thin layer. ZnS/CdS is an alternative to the conventional CdS window layer since it admits and transmits the maximum amount of photons to the junction to increase the short circuit current density (Jsc) and the efficiency of the solar cell. The electrodeposition of ZnS on fluorine doped SnO2 glass (FTO) has been previously reported and this work focuses on the electrodeposition of intrinsic CdS layers on both FTO substrate and FTO/ZnS substrate, using a three electrode cell. The electrolyte used was consisted of 0.01 mol/L Na2S2O3 and 0.1 mol/L CdCl2 at pH of 1.7 at 55 °C and the deposition potential was varied between -0.68 to -0.72 V. The samples prepared were annealed at 400 °C for 15 minutes. Both thin film structures, FTO/CdS and FTO/ZnS/CdS were analyzed by the UV-Visible spectrophotometry and photoelectrochemical (PEC) cell performance to investigate the optical absorbance and its electrical properties. The optical absorption of the samples was fallen within 2.30-2.46 eV that agree with the typical band gap energy of CdS. Among the two structures, FTO/ZnS/CdS shows lower optical absorbance in 300-900 nm region, which has been recognized as a characteristic feature for a window layer in a solar cell. For the PEC cells, made with FTO/CdS, the Jsc and Jsc×Voc values were between (18.0-1.60) ×10-6 A cm-2 and (5.94-0.38) ×10-6 AVcm-2 respectively, while for the cells made with FTO/ZnS/CdS, these values were (14.8-2.50) ×10-6 A cm-2 and (6.66-0.90) ×10-6 AVcm-2 . Although the Jsc of the FTO/ZnS/CdS based cell was relatively low, the product of Jsc×Voc was high due to its high Voc. The ZnS buffer layer facilitated the electrodeposition of well adhered, compact and pinhole free CdS window layer compared to the deposition of CdS on bare FTO. Hence, the implanting of a ZnS buffer layer on CdS/CdTe based solar cell can enhance the optoelectronic properties of the final solar cell device.
An investigation into the effect of rate of stirring of bath electrolyte on the properties of electrodeposited CdTe thin film semiconductors
(2018) Atapattu, H.Y.R.; De Silva, D.S.M.; Pathirane, K.A.S.; Dharmadasa, I.M.
Electrodeposition (ED) has been recognized as a low cost and scalable technique available for fabrication of CdS/CdTe solar cells. Photovoltaic activity of these electrodeposited semiconductor materials drastically depends on the ED growth parameters namely; electrodeposition potential, concentrations and ratios of concentrations of precursors used to prepare the bath electrolyte, pH of the electrolyte, deposition temperature and rate of stirring of the electrolyte, In order to grow thin films with good photovoltaic properties, it is essential to maintain these variables at their optimum ranges of values during electpcKlepositions. Hence, this study was conducted to investigate the dependence of the properties of electrodeposited CdTe thin film material on the rate of stirring of the bath electrolyte. The CdTe material was grown on glassfFTO (2 x3 cm2) and glassIFTO/CclS (2 x 3 cm2) surfaces in bath electrolytes containing 1.0 motIL Cd504 and 1.0 mmolit TeO, solutions at differ¬ent rates of stirring within the range of 0-350 rpm while keeping the values of pH of the electrolyte, deposition temperature and cathodic deposition potential with respect to the saturated calomel electrode at 2.3, 65 0and 650 mV respectively. After the heat treatment at 400 c'C in air atmosphere, the deposited samples with a good visual appearance were selected and evaluated based on their morphological, elemental, structural, optical and electrical properties in order to identify the optimum range of rate of stirring for electrodeposition of CdTe thin film semiconductors. Results revealed that, rates of stirring in the range of 60-85 rpm in a 100 mG volume of electrolyte containing the substrate and the counter electrodes in the center of the bath with a separation of 2.0 cm between them can ekctrodeposit CdTe layers exhibiting required levels of morphological, structural, optical and electrical properties on both glass/FTO and glasslFTO/CdS surfaces.
Necessity and relevance of precipitate free clear electrolytes for electrodeposition of CdS semiconductor materials with enhanced photovoltaic properties
(. Journal of Materials Science: Materials in Electronics, 2018) Atapattu, H.Y.R.; De Silva, D.S.M.; Pathirane, K.A.S.; Olusola, O.I.; Dharmadasa, I.M.
Cadmium sulfide (CdS) is a well-known window material used for fabrication of second generation thin film solar cells including CdS/CdTe and CdS/CuInGaSe2. Among the CdS fabrication techniques, electrodeposition is a simple, cost effective and scalable method that has been stepped towards large scale commercialization. However, the presence of precipitates in baths used for electrodeposition of CdS has been found to be a persistent problem which had produced CdS thin films with poor photovoltaic properties. Hence, an investigation was carried out to identify a set of optimum physiochemical conditions that can produce clear stable electrolyte for electrodeposition of CdS thin film semiconductors using CdCl2 and Na2S2O3 precursor salts. The study revealed that, electrolytes containing 0.10 mol/L CdCl2 and 0.01 mol/L Na2S2O3, within the pH range of 1.50-2.00 and the temperature range of 55-65 ºC can provide clear and stable electrolytes for electrodeposition of CdS thin films. Further, the results showed that, the electrical, optical, morphological and structural properties of CdS layers electrodeposited from electrolytes within above physiochemical conditions were remarkably better to those electrodeposited from the turbid electrolytic baths formed beyond the ranges of predetermined optimum physiochemical conditions.
Optimization of three growth parameters for electrodeposition of CdS thin film semiconductor; pH, deposition temperature and deposition voltage in a stable electrolyte
(Faculty of Graduate Studies, University of Kelaniya, 2015) Atapattu, H.Y.R.; De Silva, D.S.M.; Pathiratne, K.A.S.
Cadmium sulfide has been identified as the most promising window material for fabrication of CdS/CdTe and CdS/CuInGaSe2 thin film solar cells. Among vast variety of commercially available CdS fabrication methods electrodeposition (ED) is a viable technique due to its low cost and simplicity. This study focuses a procedure followed for optimization of the three growth parameters; pH of the bath solution, deposition temperature and deposition voltage for ED-CdS thin films with high photovoltaic activities utilizing CdCl2 and Na2S2O3 as cadmium and sulfur precursors respectively. Based on the two initial leading experiments, feasible pH and deposition temperature ranges for a stable electrolyte which does not promote chemical bath formation of CdS were identified to be in the ranges of 1.5-2.0 and 50-70 °C respectively. Also, using cyclic voltammetry the feasible cathodic deposition voltage was identified to be in the range of 640- 720 mV with respect to saturated calomel electrode. Consequently, the technique of the design of experiment (DOE) was carried out to establish random combinations of levels of the three electrodeposition parameters amid the previously identified parameter ranges for deposition of CdS layers via the ED technique. Finally, the electrical, optical, structural and morphological properties of the CdS thin films electrodeposited under different combinations of parameter values were investigated using photo-electrochemical cell study, optical absorption spectroscopy, x-ray diffraction method and scanning electron microscopy respectively. The results indicated that, aqueous solutions in the pH range of 1.6 to 1.8 containing 0.10 M CdCl2 and 0.01 M Na2S2O3 at 55-65 °C can successfully be used for electrodeposition of thin film CdS semiconductor materials over a cathodic deposition voltage range of 650 to 680 mV with a deposition period of 20 to 40 min.
Post deposition surface treatments to enhance the quality of polycrystalline CdTe thin films for photovoltaic applications
(Nit teria1s Chemi stry and Physics 213 (201S) 4065113, 2018) Atapattu, H.Y.R.; De Silva, D.S.M.; Pathirane, K.A.S.
Cadmium telluride (CdTe) is one of the topmost thin film polycrystalline materials used in the photo¬voltaics (PV) industry today and post deposition surface treatment has been a major step used in the production process for improving the photovoltaic quality of the CdTe material. In the present study, several post deposition surface treatment processes including CdCl2 treatment were carried out on CdTe material and the properties of the materials were then analyzed with the intension of gaining an un¬derstanding of the effect of the post deposition process on the material properties and identifying better post deposition treatment processes that can be used to improve the PV quality of the material. In this study, CdTe thin films were potentiostatically electrodeposited using the typical three electrode elec¬trolytic cell consisted of a saturated calomel reference electrode and a high purity graphite counter electrode. 3Cd504.8H20 and Te02 were used as the cadmium and the tellurium precursors respectively and CdTe layers were electrodeposited on fluorine doped tin oxide (ETD) glass substrates and glass/PTO/ CdS surfaces at pre-identified growth conditions namely; cathodic deposition potential of 650 mV, pH of 2.3 and temperature of 65'C. Subsequently, deposited samples were annealed in air with CdCl2 and thereafter, comparable samples of glass/FTO/CdTe and glass/FTO/CdS/CdTe were subjected to surface etching with diluted HCl (DH), Br2-CH3OH (BM), HNO3-H3PO4 (NP), K2Cr2D7-H2504 (DS) and K2Cr207- CH3OH (DM). Surface treated samples were then characterized for their electrical, optical, elemental, morphological and structural properties using photo-electrochemical cell measurements, optical ab¬sorption spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy and X-ray diffraction spectroscopy respectively. The study reveals that, post deposition surface treatments with BM and NP etchings enhance the material qualities of polycrystalline CdTe layers to be used for fabrication of PV devices.