Browsing by Author "Atapattu, H.Y.R."

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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 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 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 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 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.
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.
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 ℃.
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.
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.
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.