IPRC - 2015
Permanent URI for this collectionhttp://repository.kln.ac.lk/handle/123456789/156
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Item 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.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 Electro-deposition of Cadmium Zinc Sulphide at High Cadmium Ion Concentration, Low Zinc Ion Concentration, High Temperature and Low pH(Faculty of Graduate Studies, University of Kelaniya, 2015) Sarathchandra, K.A.D.M.S.; De Silva, D.S.M.; Pathiratne, K.A.S.Thin films are nanoscale materials which are widely used for solar cells and other optoelectronic devices. Cd(1-x)ZnxS (cadmium zinc sulphide) is formed by incorporating zinc ions to CdS (cadmium sulphide). Cd(1-x)ZnxS is a n-type semiconductor material which has a wider band gap than that of n-type CdS. Therefore, Cd(1-x)ZnxS can be used as a window material when application required low absorption of light and n-type semiconductor properties. Cd(1-x)ZnxS has been electro-deposited by varying cadmium ion concentration, zinc ion concentration, pH, deposition temperature and deposition time. Results reported here were based on the depositions conditions; 0.1 mol dm-3 cadmium ion concentration, 0.01 mol dm-3 zinc concentration, 2.45 - 2.50 pH and 50 °C deposition temperature. Electro-deposition experiments were carried out by Gamry ―series G 300‖ potentiostat while, working electrode was fluorine doped tin oxide/glass substrate, reference electrode was Ag/AgCl electrode and counter electrode was a semi-spherical graphite rod. The deposition voltage was identified from the cyclic voltammograms and shapes of the deposition current vs time plots. Electrodeposition reported in here was carried out at under-deposition voltages. The best values for electro-deposition parameters; voltage, pH, temperature and time were identified by observing their influence on the band gap values of the thin films deposited and the open circuit voltages of photo-electrochemical cell consisting of 0.1 mol dm-3 sodium thiosulphate electrolyte and the thin film semiconductor. A band gap range of 2.5 eV – 2.6 eV was obtained for Cd(1-x)ZnxS layer which is higher than the band gap of CdS. The open circuit voltage varied from -48 mV to -190 mV during optimization of voltage, pH, temperature and time. An X-ray diffraction spectrum has shown that Cd(1-x)ZnxS layer has a single hexagonal crystal phase. The crystal parameter, a = 4.1264 Å and it was lower than the standard CdS (a = 4.1364 Å). The results indicate that Cd(1-x)ZnxS thin films can be produced under the given conditions as a window layer for thin film solar cells in order to harvest more light and hence to improve the efficiency.Item Electrodeposition of (n-type) cadmium zinc sulphide thin film semiconductors for photovoltaic applications(Faculty of Graduate Studies, University of Kelaniya, 2015) Herath, H.M.N.A.; Pathiratne, K.A.S.Electrodeposition of thin film semiconductors have drawn increasing attention in the fabrication of solar cells due to its low cost and easy fabrication methodologies applicable in large scale production, compared to that of conventional Si solar cells. Among different types of semiconductor thin films, cadmium zinc sulphide (CdxZn(1-x)S) thin film is one of the promising wide band-gap window materials which can be used in fabrication of heterojunction solar cells. Electrodepostion of (CdxZn(1-x)S) on fluorine doped tin oxide conducting glass working electrode was carried out using aqueous solution of electro-purified salts of CdSO4, ZnSO4 and Na2S2O3. An EG & G model 636 bipotentiostat comprising of a graphite counter electrode and Ag/AgCl reference electrode were used to control the potential of the working electrode. Taking into account of the information obtained from cyclic voltammograms for the separate precursor salts, the three voltages of -0.9, -1.0 and -1.1 V were selected for electrodeposition. Thin films were deposited at each of the above voltages, using solutions with various proportions of Cd and Zn but the same concentration of Na2S2O3for three deposition time periods of 1, 2 and 3 hours. The pH and temperatures for all solutions used for depositions were maintained at 2.5 and 27 0C respectively. Photo-electrochemical cell measurements in 0.1 mol dm-3 Na2S2O3 electrolyte and UV-visible absorption spectroscopy were used to measure the open circuit voltages (Voc), short circuit current densities (Jsc) and band gaps of the electrodeposited thin films. The thin films with the highest observed photovoltaic activity of average Voc of - 0.156 V, Jsc of 2.6 A cm-2 and a band gap in the range of 2.05 to 2.28 eV were produced from electro-deposition solutions containing CdSO4, ZnSO4:and Na2S2O3 with 0.06, 0.04 and 0.10 mol dm-3respectively when deposited over a one hour period.