Chemistry
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Item ZnS Assisted ZN Doping in CdZnS Electrodeposition(Journal of Science 2019, Department of Chemistry, University of Kelaniya, Sri Lanka, 2019) Sarathchandra, K. A. D. M. S.; De Silva, D. S. M.; Pathiratne, K. A. S.Many reports have been published elsewhere on making thin films of cadmium zinc sulphide (CdZnS) using different techniques. This article summarizes a method developed to form CdZnS by incorporating electrodeposited Cd and S atoms simultaneously to the chemically formed ZnS material in the electrolytic bath at the conducting surface of fluorine doped tin oxide (FTO) coated glass substrate. Moreover, the mechanism of formation of CdZnS is proposed as a solid state reaction between electrodeposited Cd and S atoms on the glass/FTO substrate with adsorbed ZnS particles from the electrolytic bath. The precursors used for Cd, S and ZnS in the electrolyte were aqueous solutions of CdCl2, ZnCl2 and Na2S2O3. Two different methods were tested to form ZnS within the electrolyte bath where one forming ZnS in the bath at the beginning of electrodeposition of Cd and S and in the other one, ZnS is formed before the electrodeposition of Cd and S. The results of the band gap measurements show an undulation which is closer to the band gap energy of CdS indicating probable codeposition of one or more materials such as CdS, (2.42 eV), ZnS (3.7 eV), CdO (2.2 eV), and ZnO (3.2 eV) along with CdZnS. The Tauc plot resulted by the material produced in method 1 has shown an undulation at the onset of Tauc plot which is near the band gap energy of CdS indicating the codeposition of CdS with CdZnS, but the Tauc plot of CdZnS electrodeposited from method 2 has shown clear separation in band gaps from 2.44 – 2.52 eV, when the annealing temperature, the Zn2+ ion concentration in bath and the electrodeposition pH were varied. These thin films were also characterized by photoelectrochemical (PEC) cell analysis, x-ray diffraction (XRD), energy dispersive x-ray analysis (EDXA) and scanning electron microscopy (SEM) techniques.Item 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.