Browsing by Author "Hetti Arachchige, K. A."

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    The role of ascorbic acid in optimizing optoelectronic performances of CdS thin films
    (Faculty of Science, University of Kelaniya Sri Lanka, 2024) Danansuriya, D. B. U. I.; Hetti Arachchige, K. A.; Manilgama, T. T. D.; Kalingamudali, S. R. D.; Premaratne, W. A. P. J.; Jayathilaka, K. M. D. C.; Wijesundara, L. B. D. R. P.; Kumarage, W. G. C.
    Cadmium sulfide (CdS), a widely studied (II-VI) group semiconductor, has long captivated the scientific community due to its potential applications in photovoltaic (PV) devices. However, optoelectrical properties of n-CdS, such as flat band potential, and optical band gap, are crucial for enhancing solar cell efficiency. This study explores the tunability of these properties in CdS thin films through chemical bath deposition (CBD) with a mild reducing agent ascorbic acid (C6H8O6). A series of CdS thin films were deposited on fluorine-doped tin oxide (FTO) glass substrates by using various concentrations of ascorbic acid (0, 0.1, 0.01, and 0.001 mol.dm-3). The deposition chemical bath consisted of 0.1 mol.dm-3 cadmium sulfate (CdSO4) and 0.2 mol.dm-3 thiourea (CS(NH2)2) as cadmium and sulfur sources, respectively. The deposition process was conducted at 80 °C for one hour at a pH of 11. Post-deposition, the CdS films were etched in the non-conductive side of the FTO with diluted hydrochloric acid (HCl), followed by annealing at 300 °C for one hour in air. All the electrical measurements were performed in a photoelectrochemical cell comprising a CdS/0.1 mol.dm-3 Na2S2O3/Pt half-cell with an active area of 1 cm². An Ag/AgCl electrode served as the reference for all characterizations. The short-circuit current density (JSC) has shown a significant increase with decreasing ascorbic acid concentration, achieving a 155.6% enhancement with a concentration of 0.001 mol.dm-3 compared to untreated CdS. Conversely, with increasing ascorbic acid concentration the opencircuit voltage (VOC) and the flat band potential (VFB) decreased. The highest reported photocurrent power (VOC×ISC) was observed in films deposited with 0.001 mol.dm-3 ascorbic acid, showing a 150.2% improvement over untreated CdS. Scanning electron microscopy (SEM) analysis revealed that ascorbic acid-treated CdS films exhibited aggregated nanoscale particles, whereas untreated films displayed larger clusters. Consequently, the photocurrent enhancement is attributed to these morphological changes that cause higher effective surface area in the ascorbic-treated CdS thin films compared to the untreated CdS. Furthermore, Mott-Schottky analysis confirmed that all deposited films retained n-type characteristics. This study demonstrates that the electronic properties of n-CdS can be finely tuned through ascorbic acid treatment, making it a promising approach for fabricating thin film solar cells with high light-to-current conversion efficiency. The ability to control and enhance these properties is invaluable for advancing PV applications and achieving higher solar cell performances.
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    Sulphur treated single step electrodeposited Cu2ZnSnS4
    (Faculty of Science, University of Kelaniya Sri Lanka, 2024) Hetti Arachchige, K. A.; Wijesundera, L. B. D. R. P.; Kumarage, W. G. C.; Jayathilaka, K. M. D. C.; Siripala, W. P.
    Solar cells, directly converting sunlight into electricity through the photovoltaic (PV) effect, is the best alternative for the global energy crisis. Among the various solar energy materials, Cu2ZnSnS4 (CZTS) is a promising material for solar cell applications due to its unique optoelectronic properties. This study studied the possibility of the growth of quaternary CZTS thin films using a single-step electrodeposition technique for applications in PV devices. CZTS thin films were potentiostatically electrodeposited at - 0.89 V vs Ag/AgCl for 4 minutes on Titanium (Ti) substrate in a three-electrode electrochemical cell containing, 0.02 M copper (II) sulphate pentahydrate (CuSO4.5H2O),0.01M zinc sulphate heptahydrate (ZnSO4 .7H2O), 0.02 M tin sulphate (SnSO4) and 0.02 M sodium thiosulphate (Na2S2O3) at room temperature. 0.2 M tri-sodium citrate (C6H5Na3O7:Na3 - citrate) was used as a complexing agent and tartaric acid (C4H6O6) was used as pH control solution. pH of the bath was maintained at 5. The counter and reference electrodes were Pt plate and Ag/AgCl respectively. Prior to the CZTS deposition, Ti substrates were initially polished with sandpaper and then cleaned with detergent, diluted HCl, and finally cleaned ultrasonically in distilled water for 15 min. Two sets of samples were prepared by annealing as grown CZTS thin films at 550 °C for 30 minutes in N2 and H2S atmospheres respectively. As grown, annealed in N2, and annealed in H2S, CZTS films were characterized and compared using dark and light Current-Voltage (I-V) and Capacitance-Voltage (Mott-Schottky) measurements in a photoelectrochemical cell (PEC) containing a 0.1 M sodium acetate aqueous electrolyte. Grown CZTS thin films did not show any photoactive properties. However, as revealed by the I-V characteristics, films annealed in N2 produced n-type photoconductivity having Voc of 204 mV and Jsc of 20 µAcm-2 in PEC while films annealing in H2S produced p-type photoconductivity having Voc of ~ 250 mV and Jsc of ~ 110 µAcm-2 in the same PEC. This finding was further studied using Mott-Schottky characteristics. Results revealed that films annealed in N2 and H2S attribute n-type and p-type photoconductivity respectively. Further, flat band potential (VFB) values of -0.066V and +0.594V vs Ag/AgCl in the same PEC exhibited for the films annealed in N2 and H2S respectively indicating the formation of a better interface between CZTS and electrolyte for the samples annealed in H2S. In conclusion, significant photoactive enhancement in single step electrodeposited CZTS can be achieved with H2S treatment.