Browsing by Author "Kumarasinghe, K.D.M.S.P.K."
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Item 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.Item 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.Item 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.Item 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.Item Growth of CdS and CdTe thin film semiconductors and fabrication of CdS/CdTe solar cells(Faculty of Graduate Studies, University of Kelaniya, 2015) Kumarasinghe, K.D.M.S.P.K.; de Silva, D.S.M.; Pathiratne, K.A.S.; Dharmadasa, I.M.; Salim, H.I.; Abdul-Manaf, N.A.; Ravirajan, P.; Balashangar, K.Thin films of CdS and CdTe semiconductor materials were electrodeposited onto glass/fluorine doped tin oxide conducting glass surfaces using a potentiostat/galvanostat equipped with a three electrode cell. Aqueous electrolytic bath containing CdCl2 and (NH4)2S2O3 was used for the electrodeposition of CdS thin films. CdTe thin films were electrodeposited onto glass/FTO/CdS substrates from aqueous solution having high concentrations of CdSO4 and low concentrations of TeO2 and CdCl2. The glass/FTO/CdS/CdTe/Cu-Au solar cell devices were prepared by thermal evaporation of Cu and Au on CdTe surface. CdS films grown were annealed at ~400 °C for 15 minutes in air and photo-electro chemical (PEC) cell measurements were performed to identify the electrical conductivity type. Both as-deposited and annealed CdS layers were identified as n-type in electrical conduction. CdS thin films were shown enhanced PEC responses upon heat treatment. The respective band gap values for as-deposited and heat treated CdS were 2.35±0.05 eV and 2.40±0.05 eV which were close to the band gap of bulk CdS. XRD analysis of as-deposited CdS layers revealed the presence of hexagonal CdS materials with the major peak arising from (002) plane. Following the CdTe deposition on glass/FTO/CdS substrate, the surface of CdTe layers were coated with a 0.1% CdCl2 solution and structures were annealed at ~400°C for 10 minutes in air. Band gaps for CdTe layers were found to be 1.45±0.02 eV for both as-deposited and annealed samples which exhibited the band gap of bulk CdTe. There was a little improvement in cubic (220) and (311) peaks of XRD spectra of annealed CdTe layers compared to the as-deposited material, but annealing exhibited a small reduction of cubic phase preferential orientation (111). SEM images showed that CdS and CdTe layers were fairly uniform. The fabricated solar cell devices showed the efficiency of 2.1% with Voc ~330 mV, Jsc~20 mA cm-2 and FF~33% under the illumination of air mass (AM) 1.5 conditions (100 mW/cm2, 1 Sun).Item Use of electro-deposition technique for growing n-type and p-type CdS and CdTe thin film semiconductor materials for fabrication of solar cells with improved performances(Sri Lanka Association for the Advancement of Science, 2013) Kumarasinghe, K.D.M.S.P.K.; Sandaruwan, K.A.I.; de Silva, D.S.M.; Pathiratne, K.A.S.; Sivananthan, S.