Chemistry
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Item 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 nanomaterialsItem 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.Item 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.Item 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.Item 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.Item 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.Item 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.Item Electrodeposition and characterization of as-deposited and annealed CdTe thin films.(Ceylon Journal of Science, 45(2), 53–59. DOI: http://doi.org/10.4038/cjs.v45i2.7388, 2016) Kumarasinghe, K. D. M. S. P. K.; De Silva, D. S. M.; Pathiratne, K. A. S.; Salim, H. I.; Abdul-Manaf, N. A.; Dharmadasa, I. M.Thin films of CdTe semiconductor materials were grown on fluorine doped tin oxide (FTO) conducting glass substrates using the technique of electrodeposition. CdSO4 at high concentrations and CdCl2, TeO2 at low concentrations were used as precursor salts for electrodeposition. The range of deposition potentials was estimated using cyclic voltammetric measurements. The electrical, optical, structural and morphological characteristics of as-deposited and annealed CdTe thin films were characterized using photo-electrochemical (PEC) cell studies, UV-Vis spectrophotometry, X-ray diffraction (XRD) and scanning electron microscopy (SEM). These particular samples were converted from n-type into p-type after heat treatment. UV-Vis spectrometric measurements for CdTe layers indicated that, the energy band gaps of 1.45±0.02 eV for both as-deposited and annealed samples which exhibited the required optical property for fabricating CdS/CdTe solar cells. Little increase in (220) and (311) peaks of XRD spectra were observed for annealed layers compared to the as-deposited material. However, annealing exhibited a small reduction of cubic phase preferential orientation (111). The optical transmission for both as-deposited and annealed CdTe samples were about 60% for wavelengths longer than about 850 nm.Item Is it possible to grow stable p-type CdS layers suitable for fabrication of electronic devices?(University of Malaya, Malaysia, 2013) Kiriarachchi, H.D.; Lamahewage, L.H.S.N.S.; Wickramasinghe, W.A.S.; de Silva, D.S.M.; Pathiratne, K.A.S.; Dharmadasa, I.M.CdS is a technologically important wide bandgap window material with some unique properties showing highest conversion efficiencies in thin film solar cells based on CdTe and CuInGaSe2 absorber materials. n-CdS/CdTe and n-CdS/CuInGaSe2 hetero-interfaces based solar cells have demonstrated 18.7% and 20.3% lab-scale solar cell efficiencies to date. Both these devices are fabricated based on n-type CdS window material. Recent work on graded bandgap devices using p-type AlGaAs window materials experimentally demonstrated highest Voc values of 1175 mV together with highest possible FF values ~0.85, and therefore if p-CdS can be grown, it provides another route to improve solar cell efficiencies and open doors for many other electronic devices. There are several attempts to grow Cu-doped p-CdS in the literature but the follow-up research work or devices based on p-CdS are scarce. In this research programme of solar energy materials development, using electrochemical growth method, p-type CdS was observed for certain layers. However, the stability of p-type CdS is found to be weak and these results are presented and discussed in this paper.