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Item Influence of Bath Temperature on CBD-CdS Thin Films(ScienceDirect, 2016) Kumarage, W.G.C.; Wijesundera, R.P.; Seneviratne, V.A.; Jayalath, C.P.; Dassanayake, B.S.CdS thin films were grown on conducting glass substrates at different bath temperatures in order to investigate their influence on opto-electrical properties of the chemical bath deposited (CBD) CdS thin films. The CBD-CdS process was carried out with 0.001 M CdSO4, 0.002 M CS(NH2)2 and NH3 solution at different bath temperatures from 40 to 80 0C for one hour. Fabricated films were characterized using UV-Vis spectrometry, SEM, PEC cell and Profilometer. The optical transmittances of the films decreased with increasing bath temperature due to the increase of the film thickness. CdS cluster size of the thin films grown in the bath at a temperature of 60 0C was considerably larger compared to the films fabricated at other bath temperatures. The variation of optical band gap (Eg) was found to be in good agreement with cluster size variation while electrical characterizations reveal considerably high Voc and Isc values for the films fabricated at a bath temperature of 80 0C.Item Tunable optoelectronic properties of CBD-CdS thin films via bath temperature alterations(2016) Kumarage, W.G.C.; Wijesundera, R.P.; Seneviratne, V.A.; Jayalath, C.P.; Dassanayake, B.S.The tunability of the band-gap value and electron affinity of the n-CdS by adjusting the growth parameters is very important as it paves the way to improve the efficiency of CdS-based solar cells by adjusting the band lineup with other p-type semiconductors. In this respect, polycrystalline n-CdS thin films were grown on FTO glass substrates at different bath temperatures (40–80 °C) by the chemical bath deposition technique. The structural, morphological and optoelectronic properties of CdS thin films were studied using x-ray diffraction, scanning electron microscopy, UV-Vis spectrometry, profilometry, atomic force microscopy, photoelectrochemical and Mott–Schottky measurements. Absorption measurements reveal that an energy-gap value of n-CdS can be adjusted from 2.27 to 2.57 eV and Mott–Schottky measurements indicate that the flat-band potential is increased from −699 to −835 V with respect to a Ag/AgCl electrode by decreasing the deposition bath temperature from 60 to 40 °C. This tunability of optoelectronic properties of n-CdS is very useful for applications in thin film solar cells and other devices.Item Fermi‐level pinning and effect of deposition bath pH on the flat‐band potential of electrodeposited n‐Cu2O in an aqueous electrolyte(Wiley Online Library, 2016) Kafi, F.S.B.; Jayathileka, K.M.D.C.; Wijesundera, R.P.; Siripala, W.Capacitance–voltage (C–V) and modulated light-induced current–voltage measurements were employed to investigate the Cu2O/electrolyte junction of electrodeposited n-Cu2O thin films. The Mott–Schottky plots resulting from the C–V measurements revealed that the extrapolated flat-band potential of n-Cu2O films was strongly influenced by the pH of the bath where the films were grown. The flat-band potential change was 300 mV for a pH difference of 0.8 and showed that the surface chemistry at an n-Cu2O/aqueous electrolyte interface was strongly affected by the pH of the film deposition bath. In addition, current–potential measurements revealed that at the measured flat-band potential the photocurrent did not vanish for n-Cu2O films and the Fermi level at the interface was pinned due to the presence of electrically active surface states. Information on the presence of electrically active surface states and the shift in flat-band potential will be very useful for applications of n-Cu2O films in various devices.Item Electrodeposited Cu2O homojunction solar cells: Fabrication of a cell of high short circuit photocurrent(Elsevier, 2016) Wijesundera, R.P.; Gunawardhana, L.K.A.D.D.S.; Siripala, W.A Cu2O homojunction solar cell was fabricated using a consecutive electrodeposition method of deposition of an n-Cu2O film followed by a p-Cu2O film, in two different acetate baths. Both n-type and p-type film growth conditions were optimized separately to yield high photocurrents in a photoelctrochemical (PEC) cell. Further, the resulted bi-layer films were investigated in the PEC for the verification of the formation of the p-n homojunction. In addition, p-Cu2O film surfaces of the bi-layers were sulphided using Na2S and (NH4)2S in order to improve the photoresponse of the homojunction before depositing a Au film for the solar cell device. The structural, morphological and optoelectronic properties of the Cu2O films were investigated using X-ray diffraction (XRD), scanning electron micrographs (SEMs), dark and light current–voltage (I-V) and spectral response measurements and observed that the films are of good quality. Incident photon to current efficiency (IPCE) and I-V characteristics of the solar cell device demonstrated that the Cu2O homojunction can produce a high short circuit current density Jsc. However, the overall conversion efficiency of the device is low due to poor fill factor and Voc. The solar cell characteristics of the structure Ti/n-Cu2O/p-Cu2O/Au were Voc=287.0±0.1 mV, Jsc=12.4±0. 1 mA/cm2, FF=25±2% and η=0.89±0.02%, under AM 1.5 illumination. The record high Jsc value of the device demonstrates the prospect being improved the efficiency of Cu2O homojunction solar cells by optimizing deposition, pretreatment and post treatment processes.Item Methods for improving n-type photoconductivity Cu2O thin films(Semiconductor Science and Technology, 2014) Kalubowila, K.D.R.N.; Gunawardena, L.K.A.D.D.S.; Wijesundera, R.P.; Siripala, W.Electrodeposition technique is very useful for depositing n-type Cu2O thin films on various substrates. However, most of the reported n-type Cu2O thin film electrodes exhibit not only n-type photoactivity but also p-type photoactivity in photoelectrochemical cells. In this study, current?voltage characteristics and zero bias spectral response measurements were employed to investigate the possibilities to remove/minimize this unwanted p-type behaviour of n-type Cu2O thin films electrodeposited on Ti substrate. For this, prior deposition of Cu thin films on Ti substrate, low temperature annealing of Cu2O films in air and optimization of deposition bath pH were investigated. Growth of a very thin Cu film improved the n-type photosignal significantly and reduced the p-type photoresponse of the films. Films electrodeposited using an acetate bath of pH 6.1 produced only the n-type photoresponse. Low temperature annealing of Cu2O films in air improved the n-type photoresponse and it was found that annealing at 100 �C for 24 h produces the best result. These methods will be very useful to obtain electrodeposited Cu2O thin film with improved n-type photoactivity suitable for applications in thin film solar cells and other devices.Item Characterization of CuInS2 thin films prepared by electrodeposition and sulfurization with photoluminescence spectroscopy(Solar Energy Materials and Solar Cells, 2003) Garuthara, R.; Wijesundera, R.P.; Siripala, W.Potentiostatic electrodeposition and sulfurization techniques were used to prepare polycrystalline CuInS2 thin films. X-ray diffraction and photoresponse measurements in a photoelectrochemical cell (PEC) revealed that photoactive polycrystalline CuInS2 films can be deposited on Ti substrate. Photoluminescence (PL) spectroscopy was used to investigate the prepared thin films and optically characterize them. PL spectra revealed the defect structure of the samples with an acceptor energy level at 109 meV above the valance band and a donor energy level at 71 meV below the conduction band. The CuInS2 thin films prepared in this investigation are observed to be In-rich material with n-type electrical conductivity.