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 Observation of interface modification of electrodeposited p-Cu2O thin films in an aqueous electrolyte(Faculty of Graduate Studies, University of Kelaniya, 2015) Kafi, F.S.B.; Jayathilekea, K.M.D.C.; Wijesundera, R.P.; Siripala, W.Interface engineering via modification of semiconductor surfaces of junction devices is a powerful technique to improve the performance of devices. In addition, semiconductor material Cu2O has recently gained a considerable attention as a low cost semiconductor material suitable for developing thin film solar cells, water splitting in photoelectrochemical cells and gas sensors. Indeed, the possibility of relative band edge shifts of Cu2O with suitable interfacing materials will pave the way for interface engineering to improve the efficiency of those devices. In this study we have investigated this possibility of using electrodeposited p-type cuprous oxide thin films deposited using a lactate bath containing 3 M sodium lactate and 0.4 M CuSO4 at various pH values. These Cu2O films were used in a photolectrochemical cell to form semiconductor/electrolyte junctions in a 0.1 M sodium acetate aqueous solution and then to measure the flat band potential variations with the pH of the Cu2O film deposition baths. It was observed that pH value of the Cu2O film deposition bath is very sensitive to the flat band potential. This result gives a direct evidence that the surface of Cu2O film is modified at the Cu2O/electrolyte interface producing a relative band edge shift yielding the observed flat band shifts. We observed a general trend of flat band potential shift of about 350 mV in the positive direction, as the pH of the deposition bath was changed from 7 to 12.5. The observed shift in the flat band potential in the positive direction is very useful for the water splitting reaction because the valence band edge of Cu2O is shifted positively relative to the oxygen redox potential. Our observation of highest photoresponse for Cu2O thin films prepared at pH 13.5 is a direct evidence for the positive shift of the band edges. The observation of the interface modification of Cu2O in aqueous electrolyte may be further extended to other suitable interfaces for developing Cu2O based junction devices.