Physics
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Item Simultaneous control of multiple line-loads each connected separately in series with a designed unit (Control using Radio Frequency and a Mobile device)(2016) Cooray, B.N.P.; Perera, W.S.K.; Kalingamudali, S.R.D.A unit which can be connected separately in series with each load to control multiple line-loads simultaneously using Radio Frequency (RF) and a mobile device has been developed during this study. Series connected remotely controllable regulators are not widely available commercially and the few available do not have the facility to control the multiple line loads using a mobile application along with a RF remote controller and also they are very expensive and even require an alternative wiring system. The designed regulator provides the convenience of controlling the current flow through appliances connected to a single line power supply. A triac is used to control the power supplied to the load, since it can control the current flow in both halves of an AC current. The gate terminal is triggered by using a diac. A Switch Mode Power Supply, powers the active components of the regulator using the voltage drop across the triac. The Bluetooth (HC-06) and RF (315 MHz RF receiver) modules are programmed to receive inputs from the user to switch ON/OFF or control the voltage supplied to appliances such as fans and light bulbs. The Graphical User Interface enables the user to control the appliances easily and much faster than in normal usage of mechanical switches. The timer which allows the user to define time intervals for predefined output levels, can set desired levels of outputs for the appliances. This feature is not currently available in normal regulators. The suggested method facilitate simultaneous use of RF and the mobile devices as well as the ability to control several appliances with a single unit enabling energy conservation and ease of use. The cost of designing the unit with discrete components being less than US$ 17, it can be concluded that the model is cost effective since this method suggests two modes of control of the appliances along with timer settings. [1-9].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 Electrodeposited nano-crystalline cuprous oxide thin films for solar energy applications(Annual Research Symposium, University of Kelaniya., 2012) Jayathileke, K.M.D.C.; Siripala, W.; Jayanetti, J.K.D.S.Cuprous oxide thin films were electrodeposited in a cupric acetate bath and resulting films were investigated in a photo-electrochemical cell to determine the intrinsic defects density variations. It was observed that by controlling the pH value of the deposition bath, density of both Cu and O vacancies which are responsible for acceptor and donor levels respectively, can be controlled and thereby it is possible to electrodeposit either n-type or p-type cuprous oxide thin films. The study reveals that not only the pH value but also the cupric ion concentration of the acetate bath determines the nature of conductivity of the films. Structural and morphological studies revealed that nano-crystalline films of size, 100 nm, can be electrodeposited by controlling the deposition parameters. These films will be very useful in applications of solar energy converting devices.Item Water splitting by electrodeposited cuprous oxide photoelectrodes with a flower like morphology(Annual Research Symposium-University of Kelaniya, 2011) Ranasinghe J I; Siripala WMorphology of semiconductor films plays a major role in determining the efficiency of solar cell devices. Intrinsic electronic properties of cuprous oxide (Cu2O) are important for water splitting reaction using solar energy to produce environmentally clean hydrogen fuel. Especially, the n-type cuprous oxide thin films with flower-like morphology have an added advantage for efficient water splitting. In this study electrodeposition of Cu2O thin films using an aqueous H2O2 bath was investigated for the possibility of depositing films on Ti substrates with a flower-like morphology. Direct deposition of Cu2O films on a Ti substrate using a H2O2 bath is not possible. However, it was found that if a thin Cu2O film was deposited using an acetate bath prior to the film deposition, good films with a flower-like morphology can be electrodeposited. In this study, Cu2O thin films were deposited on Ti substrates in a bath containing 0.1M CuSO4 and 0.3M H2O2 at 600C. pH value of the bath was kept at 4 by adding few drops of dilute NaOH solution. SEM pictures show the flower ?like morphology of the films. V-I characteristics and the spectral responses confirmed the n-type behavior of the deposited films. Possibility of water splitting using n-type Cu2O films without applying an external bias is demonstrated in this study. The performance of the films in a photoelectrolytic solar cell with a flower like morphology is compared with the films with normal morphology.Item Fabrication and characterization of electrodeposited nanocrystalline/microcrystalline cuprous oxide thin films(Proc. Annual Research Symposium, University of Kelaniya, 2008) Jayathilaka, K.M.D.S.; Wanninayake, W.T.M.A.P.K.; Siripala, W.; Jayanetti, J.K.D.S.The quest and need for clean and economical energy sources have increased interest in the development of solar energy applications. In particular, direct conversion of solar energy to electrical energy and chemical energy using semiconductor photoelectrodes has attracted attention for many decades. Among the various metal oxide materials for solar energy applications, a promising material is cuprous oxide (Cu2O) and is one of the oldest known semiconductors. It is low cost and non toxic and its component elements are readily available. It has a direct band gap of about 2 eV and a high optical absorption coefficient. Nanocrystalline thin films increase the effective surface area of the films as compared with the microcrystalline thin films. Therefore preparation of nanoparticles of Cu2O is of special importance to improve the solar energy conversion efficiency. In this study, Cu2O films were deposited electrochemically on Ti substrates. In this study, a simple electrochemical technique was developed to fabricate the Cu2O/CuxS heterojunction to be used in a thin film photovoltaic solar cell. Electrodeposited Cu2O thin films on Ti substrates were sulphided by directly applying an aqueous solution of Na2S on to Cu2O films and annealed at 200 0C for a few minutes. Then the samples were exposed to NH4S gas for a few seconds. It was observed that the photovoltaic properties and the diode characteristics of nano/micro/Cu2O/CuxS structures were better than that of micro/Cu2O/CuxS structures. The maximum conversion efficiency of the micro/Cu2O/CuxS cell was 0.12% (Voc= 240 mV, and Isc= 0.86 mA/cm2) and that of the nano/micro/Cu2O/CuxS cell was 0.28% (Voc= 420 mV, and Isc= 2.1 mA/cm2) under AM1.5 illumination.Item Electrolyte Electroreflectance Study of CdIn2Se4 Liquid Junction Solar cells(American Physical Soc. Meeting, Los Angeles,USA, 1983) Tomkiewicz M; Siripala WItem The Interrelation Between the Potential Distribution and the Dark Charge Transfer Across n-TiO2 - Aqueous Electrolyte Interface(Symposia on Photoelectrochemical Process and Measurements Techniques for Photoelectrochemical Solar Cells, 1981) Tomkiewicz M; Siripala W