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

Now showing 1 - 20 of 42

A low cost electro-deposition procedure for growth of n- type cds semiconductor material used in fabrication of cds/cdte thin film solar cells
(Book of Abstracts, Annual Research Symposium 2014, 2014) Chaturangi, R.A.; Kumarasinghe, K.D.M.S.P.K.; Pathiratne, K.A.S.; de Silva, D.S.M.
CdS/CdTe thin film solar cells have exceeded the efficiencies of nearly 20% and 16% in laboratory and industrial scale devices respectively. Owing to the large band gap of 2.42 eV of CdS semiconductor, it is used as the window material in these devices. A low cost electro-deposition experimental procedure which utilizes electro-purified analytical grade chemicals and a method which does not produce wastes need to be discarded into the environment is described here. CdS thin films with thickness <100 nm was potentiostasticaly electro-deposited utilizing EG & G Princeton Applied Research Model 366 A bipotentiostat on fluorine doped tin oxide(FTO) conducting glasses which function as working electrodes in three electrode cells comprising of silver/silver chloride reference electrodes and graphite counter electrodes. Prior to use, conducting glasses were mechanically cleaned in a dust free environment. Electro-purified CdCl2 and Na2S2O3 were used as the Cd and S sources for depositing thin films of CdS on FTO glasses. Ranges of working electrode potentials, relative proportions of the two salts and the pH in the electroplating baths which could yield CdS thin films that showed satisfactory photovoltaic activities were estimated. Bath temperature and deposition time were kept at previously established values of 470C and 1 hour for all depositions. Also all CdS thin films were annealed at 400 0C for 10 minutes in air prior to estimation of their photovoltaic properties. It was found that, deposition potentials in the range of -1300 to �1500 mV with respect to silver/silver chloride electrode, concentration ratios of [Cd]/[S] = 10:1 to 15:1 having [Cd] concentrations in the range of 10 to 15 mmol dm-3 in solution and pH in the range of (1.2�1.4) in the plating bath could produce CdS thin films with optical band gaps lying in the range of (2.3 � 0.1) eV. X-ray diffraction studies showed that all CdS deposits were to consist of cubic lattice structure. Current- Voltage measurements indicated that, the thin films grown were of n-type in electrical conductivity. Photo-electrochemical cell experiments produced open circuit voltages and short circuit current densities in the ranges of -150 to -250 mV and 3.75 to 20 ?A cm-2 respectively indicating the level of photovoltaic activity that the deposits of CdS could demonstrate. Studies are in progress for further improvements of the electro-deposition procedure.
Chain tilt and surface disorder in lamellar crystals. A FTIR and SAXS study of labeled long alkanes
(Macromolecules, 2002) de Silva, D.S.M.; Zeng, X.; Ungar, G.; Spells, S.J.
Small-angle X-ray scattering (SAXS) and infrared spectroscopy (IR) are employed in a study of chain tilt and disorder in solution-crystallized long alkanes C198H398 and C12D25C192H384C12HD24 in extended and once-folded conformations. The as-grown crystals have chains perpendicular to the lamellar surface, but around 90 °C they start tilting relative to the layer normal. The tilt increases gradually to reach 35° just below melting point. The end-labeled alkane allows independent IR probing of molecular disorder at the deuterated surface layer and in the hydrogenous interior of the crystals. The initially small splitting of the CD2 bending mode doublet and the presence of a singlet component indicated a rough surface in as-grown crystals, with considerable translational disorder. The increase in splitting and decrease in absorbance of the singlet which occur on annealing at progressively higher temperatures showed a steady improvement in translational surface order, concomitant with an increase in chain tilt angle. Thus, it is concluded that the absence of tilt in as-grown crystals is not due to high surface order, as in the case of shorter odd n-alkanes, but rather to high nonequilibrium surface disorder with chain ends or folds protruding out of or sunk beneath the surface. It is also concluded that chain tilt only becomes necessary as the crystal surface becomes translationally more ordered and the crystal-amorphous interface sharpens. IR also demonstrated the reversible increase in conformational disorder in the surface layer with increasing temperature and an almost negligible increase in the crystal interior. The gradual change in tilt angle and the existence of noncrystallographic basal planes is interpreted in terms of translational molecular disorder at the surface. The increased central SAXS scatter during the tilting process indicates the creation of voids associated with ridge formation and corrugation of the lamellae.
Characterisation of spinifex (Triodia pungens) resin and fibres
(Australasian Polymer Symposium, Cairns, QLD, Australia, 2009) de Silva, D.S.M.; Memmott, P.; Flutter, N.; Martin, D.
Spinifex grasses have been largely ignored as a sustainable resource despite their widespread distribution throughout Australia. This project involves an in-depth study of the structure and properties of both the leaf and resinous components of various spinifex species and an investigation into the preparation and properties of Spinifex-based composite materials. The present work is comprised of two components, analysis of the resin and mechanical testing of various fibrous components. Resin of the soft Spinifex species (Triodia pungens) was extracted from the resinous stems of Spinifex grasses into methanol by soxhlet extraction. The dried extracts were chromatographed on silica gel, eluted with the solvent mixture of hexane and methanol with increasing polarity to give ten fractions. Resin was also extracted directly by soaking the resinous stems for 8 hours in hexane and methanol in order to study the polar and non-polar volatile compounds. The chemical composition of the fractions of the resin has been studied by means of GC-MS and LC-MS. ATR-FTIR spectroscopy was used to identify the functional groups present in the resin. Thermal analysis was also performed using DSC. GC-MS chromatograms revealed
A comparison of performance between chemical bath deposited and electrochemical bath deposited CdS thin films in CdS/CdTe thin film solar cells
(The U.S. Workshop on the Physics and Chemistry of II-VI materials, 2013) Pathiratne, K.A.S.; de Silva, D.S.M.; Kumarasinghe, K.D.M.S.P.K.; Dasanayake, B.S.; Colegrove, E.; Xin Zheng, R.D.; Sivananthan, S.
Dilution wave and negative-order crystallization kinetics of chain molecules
(Physical Review Letters, 2000) Ungar, G.; Mandal, P.K.; Higgs, P.G.; de Silva, D.S.M.; Boda, E.; Chen, C.M.
We show that the crystal growth rate of a very long-chain n-alkane C198H398 from solution can decrease with increasing supersaturation and follow strongly negative order kinetics. The experimental behavior can be well represented by a theoretical model which allows the molecule to attach and detach as either extended or folded in two. The obstruction of extended-chain growth by unstable folded depositions increases disproportionately with increasing concentration. As a consequence of this abnormal kinetics, a “dilution wave” can propagate and trigger a folded-to-extended-chain transformation on its way.
Effect of Concentration of Cd2+ on the Material Properties of CdTe Thin Films Electrodeposited via a Two Electrode Electrolytic Cell
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Wedisinghe, K.C.; Atapattu, H.Y.R.; de Silva, D.S.M.
Cadmium telluride (CdTe) is a vital semiconductor material which can absorb most of the electromagnetic radiation of solar energy spectrum to yield more efficient solar cells. Among the thin film fabrication methods, electrodeposition is an emerging technique to produce good quality CdTe materials using either two or three electrode system. This study was performed using the two electrode electrolytic system to investigate the effect of Cd2+ concentration on the material properties of CdTe thin films to enhance its photovoltaic activities. Electrodepositions of CdTe were carried out in an aqueous electrolyte which was prepared utilizing analytical grade CdSO4 as the cadmium and TeO2 as the tellurium precursors. Fluorine doped tin oxide coated conducting glass (1×3 cm2) and high purity carbon electrode were used as the working (cathode) and counter electrodes (anode) respectively in the electrolytic cell used for the depositions. The concentration of TeO2 was maintained around 1 mmol/L throughout while varying the CdSO4 concentration from 1.00 mol/L to 1.50 mol/L. pH of the electrolyte was initially adjusted to 2.2 and depositions were carried out in the cathodic potential range of (1.33 - 1.37) V at 65 °C while stirring at continuous stirring rate of 60 rpm. The resulting electrodeposited CdTe layers were heat treated for 10 minutes at 400 °C in air and subsequently, their optical, electrical morphological and structural properties were studied using UV-visible spectrophotometry, photo-electrochemical cell, scanning electron microscopy and X-ray diffraction spectroscopy. As elucidated by the results, at the deposition potentials of 1.34 V and 1.35 V, the short circuit current and open circuit voltage values were increased with the increasing of concentration of Cd2+ from 1.00 mol/L to 1.25 mol/L while the band gap energy reached to its theoretical value of 1.50 eV.
Effect of pretreatments on extending the shelf life of minimally processed “Ela Batu” (Solanum surattense)
(Tropical Agricultural Research and Extension, 2007) Dharmabandu, P.T.S.; de Silva, D.S.M.; Wimalasena, S.; Wijesinghe, W.A.J.P.; Sarananda, S.
Due to the cumbersome nature of the cleaning process and high time consumption for the preparation, most Sri Lankan housewives are reluctant to prepare Solunum surattense (Sinh. Elabatu) as a vegetable for their diet. If S. surattense is available in „ready to cook‟ form it would become a popular vegetable among Sri Lankan housewives. Studies were carried out to identify the best conditions for minimal processing of S. surattense. As pre-treatments 2% (w/v) calcium chloride solution, 0.6% (w/v) turmeric solution, 1% (w/v) vinegar solution, 2% (w/v) calcium chloride + 0.6% (w/v) turmeric solution and 2% (w/v) calcium chloride +1% (w/v) vinegar solution were used. Low density polyethylene (LDPE) pouches (gauge 150) were used to pack pre-treated samples and stored them at 8ºC. In all the pre-treated samples stored at 8ºC, Salmonella and E. coli were absent and coliform counts were at acceptable levels. Sensory evaluation of cooked pre-treated samples showed that the sample pre-treated with 2% (w/v) calcium chloride was the best. In addition to shelf life, colour, and degree of browning of the treatments were also acceptable. Treating S. surattense cut fruits with 2% (w/v) calcium chlo-ride solution before packing in LDPE pouches and storing in 8ºC found to be the best method for extending shelf-life of the fruit. The product could be kept for seven days.
Effect of stirring rate of the electrolyte on properties of electrodeposted CdS layers
(International photovoltaic solar energy conference-Solar Asia, Pune, India, 2015) Atapattu, H.Y.R.; de Silva, D.S.M.; Pathiratne, K.A.S.; Dharmadasa, I.M.
Effect of stirring rate of the electrolyte on properties of electrodeposted CdS layers
(Springer US, 2016) Atapattu, H.Y.R.; de Silva, D.S.M.; Pathiratne, K.A.S.; Dharmadasa, I.M.
CdS is the most matching window material available for the CdTe absorber layer of CdS/CdTe solar cells and electrodeposition is a promising technique adaptable for fabrication of thin films of CdS owing to its simplicity, low cost, scalability and manufacturability. The quality of electrodeposited thin film semiconductor layers depends significantly on the electrodeposition potential, concentrations of precursor salts, pH, temperature and the rate of stirring of the electrolyte. In this study, the attention was focused on the effect of “stirring rate of electrolyte” since it has not been studied in detail in the past, despite of its strong relation to the rate of mass transport towards the working electrode where the thin film semiconductors are electrodeposited. This study was carried out via electrodepositing of CdS thin layers on fluorine doped tin oxide conducting glass working electrodes at different rates of stirring of the electrolyte while keeping the rest of the electrodeposition parameters unchanged at a previously identified set of values. The morphological, electrical and optical properties of the CdS layers grown at different stirring rates were used to determine the effect of stirring rate on the quality of CdS layers. The study revealed that, a stirring rate in the range of 60–125 rpm which produced orderly flows in the electrolyte around the working electrode (1 × 3 cm2) placed at the center of a 100 ml electrolytic bath with a distance of 2 cm apart between the graphite counter electrode and the conducting glass electrode could produce good quality CdS layers when electrodeposition was carried out at a cathodic deposition potential of 660 mV with respect to the saturated calomel electrode. The concentrations of CdCl2 and Na2S2O3 in the bath used were 0.10 and 0.01 M respectively. The temperature and pH of it were 60 °C and 1.80 respectively.
Effect of Thermal Annealing on Electrodeposited CdS and CdS/CdTe Heterojunction
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Atapattu, H.Y.R.; de Silva, D.S.M.; Pathiratne, K.A.S.
At present CdS/CdTe based solar cells have a significant commercial impression due to its lowcost, scalability, manufacturability and simplicity. Nevertheless, it is essential to elevate the optoelectronic qualities of CdS and CdTe materials and the interface properties of CdS/CdTe heterojunction and ultimately the efficiency of the solar cells. In this regard thermal annealing is one of the key steps to be considered in order to enhance the material and heterojunction properties. Hence, in this study, the effect of thermal annealing on electrodeposited CdS and CdS/CdTe heterojunction was investigated. CdS and CdTe semiconductor layers were potentiostatically electrodeposited on bare fluorine doped tin oxide (FTO) glass substrates and FTO/CdS respectively using the typical three electrode electrolytic cell. For both layers, saturated calomel electrode and high purity (99%) graphite rod were used as reference and counter electrodes respectively. 0.10 mol/L CdCl2 and 0.01 mol/L Na2S2O3 were used as Cd and S precursors respectively to produce CdS thin films while 1.35 mol/L CdSO4 and 1.0 mmol/L TeO2 were used as Cd and Te precursors respectively for CdTe. CdS layers were grown at cathodic deposition potential of 660 mV at pH 1.6 and temperature of 55 °C. Afterwards, one set of electrodeposited CdS samples was conveyed for fabrication of CdS/CdTe heterojunction. CdTe layers were grown on CdS layers at cathodic deposition potential of 650 mV at pH 2.3 and temperature of 65 °C. Subsequently, thermal annealing was carried out for both CdS and CdS/CdTe at three different temperatures; 390, 400 and 410 °C, for each annealing three different time periods; 10, 15, 20 min were considered. After the process of annealing all the samples were inspected for their optical, electrical and morphological properties using the techniques of optical absorption spectroscopy, photoelectrochemical cell and scanning electron microscopy respectively. According to the results, the optimum annealing conditions which yielded good optoelectronic qualities for CdS and CdS/CdTe were found to be 400 °C, 15 min and 390 °C, 15 min respectively.
Effects of pretreatments on extending the self life of minimally processed Rhisomes of Lasia spinosa
(Institute of Chemistry Ceylon, 2008) Liyanage, S.; Wimalasena, S.; de Silva, D.S.M.
The effects of self-poisoning on crystal morphology and growth rates
(Advances in Polymer Science, 2005) Ungar, G.; Putra, E.G.R.; de Silva, D.S.M.; Shcherbina, M.A.
Recent extensive experimental work and the limited theoretical studies of the phenomenon of self-poisoning of the crystal growth face are reviewed. The effect arises from incorrect but nearly stable stem attachments which obstruct productive growth. Experimental data on the temperature and concentration dependence of growth rates and the morphology of long-chain monodisperse n-alkanes from C162H326 to C390H782 are surveyed and compared to some previously established data on poly(ethylene oxide) fractions, as well as on polyethylene. The anomalous growth rate minima in both temperature and concentration dependence of growth rates are accompanied by profound changes in crystal habits, which have been analysed in terms of growth rates on different crystallographic faces, and in terms of separate rates of step nucleation and propagation. In some cases non-nucleated rough-surface growth is approached. The phenomena covered include “poisoning” minima induced by guest species, the “dilution wave” effect, autocatalytic crystallization, pre-ordering in solution, two-dimensional nucleation, and the kinetic roughening and tilt of basal surfaces.
Electrochemical deposition and characterization of CdTe thin films
(Book of Abstracts, Annual Research Symposium 2014, 2014) Kumarasinghe, K.D.M.S.P.K.; Chinthana, H.R.D.; de Silva, D.S.M.; Pathiratne, K.A.S.
The semiconductor cadmium telluride (CdTe) has been widely used in applications of photovoltaics, sensors and detectors because of its direct band gap with high atomic number and electron density. With its narrow and direct band gap, stability with high absorption coefficient and other optoelectronic properties, it is the most ideal material for photovoltaic structures. A solar cell made of polycrystalline CdTe thin film is one of the most promising low cost materials for photovoltaic applications. CdTe was grown using different techniques such as physical vapor deposition, chemical vapor deposition, molecular beam epitaxy, close space sublimation, liquid phase deposition and electrodeposition. Electrodeposition has demonstrated numerous advantages due to its simplicity, low cost and scalable manufacturing techniques. CdTe films have been electrodeposited on fluorine doped tin oxide (FTO) coated glass substrates which have sheet resistance less than 20 ?/sq. A conventional three electrode cell was used for the deposition where a high purity graphite rod and saturated calomel electrode (SCE) were presented as the counter electrode and as the reference electrode respectively. Prior to the deposition of semiconductor layers FTO glass substrates were cleaned by a sequence of steps which included wiping out with detergent, ultrasonic washing in detergent solvents and then with deionised water followed by degreasing using acetone, methanol and isopropyl alcohol. CdTe thin films have been prepared by potentiostatic electrodeposition from acidic solution containing CdSO4, CdCl2 and TeO2. The deposition mechanism was investigated by cyclic voltammetry. The thickness of the film can be controlled by the charge passed during the deposition, and it is possible to obtain p-type and n-type materials by changing the deposition potential. Photoelectrochemical (PEC) cell measurements were carried out in order to determine the electric conductivity type of electrodeposited layers.The PEC values were determined for both as deposited and heat treated materials.The electrodeposited thin films were characterized and investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible absorption spectroscopy. The CdTe thin films were found to posses a bandgap of (1.44�0.02) eV, which is in a good accordance with those reported in the literature.
Electrochemical deposition of CdS thin films using ammonium thiocynate as the sulfur source
(Book of Abstracts, Annual Research Symposium 2014, 2014) Ariyasingha, N.M.; de Silva, D.S.M.; Pathiratne, K.A.S.
Use of a complexing agent containing sulfur atoms which can form a charge complex with Cd2+ ions could provide a condition necessary to bring atoms or ions of both the elements Cd and S together in the form of a charge complex to the electrode surface thereby facilitating the formation of CdS on the electrode surface over other materials. In the present study, electrochemical conditions necessary to electrodeposits thin films of CdS using ammonium thiocynate as the complexing agent was studied.
Electrochemical deposition of CuInTe2 layers for applications in Thin Film Solar Cells
(Sri Lanka Association for the Advancement of Science, 2010) Chandima, A.M.B.; Pathiratne, K.A.S.; Dharmadasa, I.M.; Wijesundera, R.P.; de Silva, D.S.M.
Electrodeposition of CdTe thin films using a two electrode system
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Wedisinghe, K.C.; Atapattu, H.Y.R.; de Silva, D.S.M.
Cadmium telluride (CdTe) is a promising material for thin film solar cell applications due to its ideal band gap of ~1.5 eV which has the ability to absorb the maximum of the solar spectrum and higher conversion efficiency of sun light. Among the various deposition techniques available to produce CdTe semiconductor material in commercial quantities, electrodeposition has drawn more attention due to its simplicity, scalability and easy control of the material properties through growth parameters; applied potential, temperature, pH and the composition of the bath etc. Since the reference electrode could be a potential impurity source in the conventional three electrode electrolytic system, this study was mainly focused on the use of two electrode electrolytic system to determine suitable deposition potential and pH ranges for growth of CdTe thin film while avoiding the influence of impurities. The two electrode electrolytic cell consisted of, fluorine doped tin oxide coated glass substrate as the working electrode and 99.99% pure carbon electrode as counter electrode was used for the deposition of CdTe thin films. The electrolyte contained analytical grade reagents of 1.25 mol/L CdSO4 and 1.0 mmol/L TeO2 as cadmium and tellurium precursors respectively. Prior to electrodepositions, pH of the electrolytic baths were varied from 2.0 to 2.4 at 25 °C. While changing the cathodic deposition potentials in the range of (1.30 - 1.37) V, the CdTe depositions were carried out stirring the bath at 60 rpm and at the temperature of 65 °C. Following the heat treatment of the samples for 10 minutes at 400 °C in air, the characterization of CdTe thin films was carried out based on optical absorption, photo-electrochemical cell, X-ray diffraction and scanning electron microscopic studies. The results of the study indicate that, CdTe thin films can be successfully grown in the cathodic potential range of (1.34 -1.35) V and at a pH of 2.2 using two electrode electrolytic system.
Electrodeposition of well-adhered CdTe thin films for solar cell applications
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Atapattu, H.Y.R.; de Silva, D.S.M.; Pathiratne, K.A.S.
Among the second generation thin film photovoltaics, CdS/CdTe based solar cell device is one of the leading contenders for large scale commercialization. Since the CdTe is the crucial absorber material of the foregoing device, it is essential to maintain a well-adhered CdTe layer to obtain high photovoltaic activities. If not, loosened CdTe layers with numerous pinholes can reduce the electrical, optical, structural and morphological properties of the material and hence extinguish the entire activities of CdS/CdTe solar cells. In the present study, an electrodeposition procedure was developed to fabricate welladherent CdTe layers to the substrate using the typical three electrode electrolytic cell. A fluorine doped tin oxide conducting glass substrate (7Ω/sq.) with dimensions of (1×3) cm2 was used as the working electrode in the cell. A saturated calomel electrode and a high purity graphite rod served as reference and counter electrodes respectively. All the electrodepositions were carried out using an aqueous solution containing 1.0 mol/L CdSO4, 1.0 mmol/L TeO2 and 5.5 mmol/L CdCl2. Based on the cyclic voltammetry studies and the stoichiometry of the proposed chemical reaction which forms CdTe material, the possible cathodic deposition potential (CDP) and pH ranges were identified to be in the ranges of 550-710 mV and 1.4-2.4 respectively. Henceforth, CdTe layers were electrodeposited at above mentioned conditions at temperature of 65 °C and subsequently annealed in air at 400 °C for 10 min. Thereafter, by considering the physical appearance of deposited CdTe layers and their adhesiveness upon a high pressure N2 flow, the feasible values for CDP and pH were found to be in the ranges of 590-660 mV and 2.0-2.4 respectively. To further fine-tune the values for CDP and pH, a series of CdTe layers were deposited at above feasible growth conditions and inspected for their electrical, optical, structural and morphological properties using the methods of photo-electrochemical cell, optical absorption spectroscopy, X-ray diffraction and scanning electron microscopy respectively. Results revealed that, the optimum CDP is in the range of 620-660 mV and pH is in the range of 2.1-2.3 to exhibit good photovoltaic qualities.
Electrodeposition of ZnS Thin Films by Complexing Agent‑Free Electrolyte Containing Sodium Thiosulfate as the Sulfur Precursor
(Journal of Electronic Materials, 2021) Madhuwanthi, H.M.L.U.; Mahanama, G.D.K.; de Silva, D.S.M.
Thin films of zinc sulphide (ZnS) were prepared by a facile, economical, and scalable electrochemical method as a buffer layer for a CdS/CdTe based solar cell. Herein, a three-electrode cell in a complexing agent-free electrolyte containing 0.1 mol/L Na2S2O3 and 0.1 mol/L ZnSO4 was employed for the deposition of ZnS. The electrodeposition conditions (temperature: 30°C, pH: 4.2, cathodic potential: −1.10 V and deposition time: 90 min) were identified to grow an ideal thin film of ZnS on fluorine-doped tin oxide (FTO)-coated glass substrate, applying moderate stirring of 60 rpm. In material characterization of heat-treated samples (300°C, 10 min), the optical absorption measurement depicted a direct energy bandgap of 3.64 eV with low light absorbance and a blueshift from bulk ZnS. Scanning electron microscopy and atomic force microscopy studies demonstrated the uniform distribution of ZnS grains over the FTO glass substrate, and x-ray diffraction analysis revealed an amorphous structural nature of ZnS. The charge carrier density and flat-band potential of the ZnS material were determined as 1.19 × 10− 19 cm− 3 and −0.59 V, respectively, by Mott–Schottky analysis.
Eletrodeposition of CdS thin films using different sulfur sources for CdS/CdTe solar cells
(Book of Abstracts, Annual Research Symposium 2014, 2014) Kumarasinghe, K.D.M.S.P.K.; Chinthana, H.R.D.; de Silva, D.S.M.; Pathiratne, K.A.S.
Cadmium Sulphide (CdS) and Cadmium Telluride (CdTe) are two promising photovoltaic materials for thin film solar cells. CdS is a wide band gap n-type semiconductor, which can act as a window layer. The function of CdS is to allow energetic shorter wavelength photons to pass for the incidence at the hetero-interface with minimum absorption loss. The high optical band gap of CdS (~2.42 eV) assists this function. Among the different techniques, electrodeposition is one of the most suitable low cost methods, because the material can be deposited on the desired area of the substrate thus providing a film of reproducible quality. CdS films were prepared by electrodeposition technique from CdCl2 as cadmium precursor and Na2S2O3 or (NH4)2S2O3 as sulfur precursor in aqueous medium. For the electrodeposition of CdS three electrode system was employed using glass/FTO as the working electrode (cathode), saturated calomel electrode as a reference electrode and high purity graphite rod as a counter electrode (anode). Electrochemical deposition method through the influence of the concentration of precursor species, deposition potential, deposition temperature and pH offers excellent control over the properties of thin CdS layers using a potentiostatic approach. The changes in the morphology and properties of the films prepared from different sulfur sources were studied. The CdS layers grown using Na2S2O3 as sulfur precursor show thickness below 100 nm. Voc and Jsc obtained for initial solar cells with CdS films grown using Na2S2O3 as sulfur precursor had higher values compared to that of CdS semiconductor layers grown using (NH4)2S2O3. The photoelectrochemical (PEC) cell measurements were used to identify the electrical conductivity type of the layers and it was found that as grown and heat treated material layers were of n-type for both CdS layers which were grown using different sulfur sources. Upon heat treatment, the material layers show enhanced PEC signal indicating improved optical properties. The optical absorption measurements were carried out in order to evaluate the band gap of the resulting materials. All samples exhibit a band gap value of 2.42 0.08 eV without any noticeable differences as expected. Electrodeposited CdS films were characterized by XRD for determination of bulk structure and SEM for surface analysis.
Energy efficient hybrid water heating system
(2016) Piyumal, P.L.A.K.; Nagahapitiya, N.W.H.G.B.; Jayatissa, N.W.K.; de Silva, D.S.M.
As the world’s energy resources are diminishing, we need to find greener solutions through renewable energy sources that can generate electricity for heating, lighting homes and for a variety of commercial and industrial uses. Among many types of renewable energy resources, such as wind and solar energy, are constantly replenished and will never run out. At present we are experiencing an electrical energy shortage in Sri Lanka. However, we are still wasting so much of electrical energy in spite of the above crisis. The University of Kelaniya has many cafeterias. The cafeteria attached to the Gymnasium is the largest food and refreshments supplier in the university. The main refreshment for the students is hot tea. Hence, every day, every hour, the canteen has to produce a large number of cups of tea by using considerable amount of electrical energy for boiling water. Hence, the purpose of this project is to minimize the electricity consumption in the boiler using freely available sunlight. Initially, the project was focused to power the boiler using a photovoltaic array. Even though this method was straight forward, investigations have shown that this method was not financially viable. Hence, the next approach was to utilize solar thermal energy to heat the make-up water to the boiler which is significantly cheaper to implement than the previous. Fresh water is circulating through the heat exchanger unit placed on the top of the roof of the cafeteria. Heated water is fed to the boiler as make-up water. Although the heating system is unable to produce boiling water. It is capable of producing nearly half of the energy requirement for boiling the water. A temperature sensor was placed to measure the boiler temperature and the output of the sensor is fed to the heating element to maintain the boiler temperature at 373 K. According to the observation it is clear that make-up water temperature in the morning is 332 K which is little lower than the temperature of make-up water in the afternoon which is 342 K due to overnight cooling of the storage tank. Therefore, morning electricity consumption of the boiler is little larger than the evening. The average daily hot water consumption for making tea is approximately 78 liters in the morning and 88 liters in the afternoon. According to the calculations, it can be shown that the hybrid system is capable of saving 50% of electrical energy of the boiler. It can be concluded that the total energy provided by the solar heating system or the saving of the system is around 2450 kWh per annum.