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Co-sensitization performance of dye sensitized solar cell based on combination of natural dyes extracted from grapes and green tea
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Shakya, M. D. P. A.; Jayathilaka, K. M. D. C.; Wanninayake, W. T. M. P. K.; Kumara, R.; Siripala, W. P; Wijesundera, L. D. B. R. P.
The global energy crisis is a pressing issue that is likely to intensify in the future. Researchers are actively exploring alternative energy sources to create a more sustainable and secure future for the world's energy needs. The advantages of Dye Sensitized Solar Cells (DSSC) include simple, easy and cost-effective manufacturing, the ability to use flexible substrate, and the possibility to attain reasonable conversion efficiency. Their unique properties make them a promising solution for addressing energy shortages and advancing renewable energy technologies. The current efficiency of DSSCs is low, however dye modification can enhance their photoactive performance. Dye modification enhances the dye's optical characteristics and photoconductivity. Co-sensitization is a chemical approach to improve DSSC performance by using two or more dyes with distinct optical absorption properties. This study explores co-sensitized DSSC using natural dyes to enhance photoactive performance. The TiO2 was prepared by mixing TiO2 powder (Titanium (IV) dioxide), Acetic acid, and Ethanol. To study the effect of natural dyes on the photoelectric conversion efficiency of DSSCs, extracts of green tea and grapes were used as sensitizers. The photovoltaic characteristics of green tea and grape dyes were studied separately and then blended in a cocktail at four various volume ratios of tea and grapes dyes 1:4, 2:3, 3:2, and 4:1 to determine the best combination. The solar cell devices were characterized using absorbance spectra, electrochemical impedance, and current density-voltage (J-V) curves. UV-visible spectra were taken from the PekinElmer Ultraviolet and Visible Spectroscopy (UV/VIS) Lambda 365. J-V and electrochemical impedance spectroscopy measurements were taken with a Gammy series G 300 potentiostat using ELS300 software. A combination of green tea and grape dyes can increase absorbance and broaden the light absorption spectrum more than a single dye. The 1:4 tea-grape mixed dye demonstrated the best DSSC efficiency value as well as the highest photocurrent value. Cosensitization resulted in a conversion efficiency of 0.0198%, photocurrent density (JSC) of 230 µA/cm2, open circuit voltage (VOC) of 0.28 V, and fill factor of 30% while efficiency also increased from 0.0058% to 0.0198%. The results show that a higher anthocyanin composition relative to chlorophyll can improve DSSC efficiency. The impedance results show that the dye mixture decreases internal resistance, which is consistent with the observed cell efficiencies. Furthermore, the best results were obtained with an acidified cocktail at pH 3 with the same volume ratio of the non-acidified cocktails. Hydrochloric acid was used for acidification. The study reveals that co-sensitization holds significant potential for the future development of DSSCs.
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.
Effect of temperature and pH on the wettability of electrodeposited n-type cuprous oxide films
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Kapukotuwa, K. M. V. Y.; Shakya, M. D. P. A.; Jayathilaka, K. M. D. C.; Bandara, T. M. W. J.; Wijesundera, L. B. D. R. P.
This research considers the temperature effect on wettability properties of electrodeposited n-type cuprous oxide (n-Cu2O) thin films, having focus on the role of bath pH and annealing temperature in their different values. In this research, n-type Cu2O films were produced using a three-electrode electrochemical cell containing an aqueous solution of sodium acetate and cupric acetate at 55°C, with the change in bath pH carried out by adding diluted acetic acid and NaOH. The films were deposited on titanium substrate at -200 mV vs Ag/AgCl for 40 minutes, and after that annealed in an air atmosphere at different temperatures increasing by 50°C increments starting from 100°C. The results of the photoresponse measurements confirmed the n-type nature of cuprous oxide. Crystal structure was determined by X-ray diffraction and the detailed surface morphology of the Cu2O thin films were examined using SEMs, which relate to the wettability characteristics of this material. The sessile drop method, utilizing ImageJ software based on Young's equation, showed that the contact angle measurements of wettability in the n-Cu2O substrates greatly depended on the pH of the electrodeposition bath and annealing temperature. The results revealed that the n-Cu2O films were hydrophilic when films were prepared at pH of 5.6, 6.23, 6.4, and 6.6. Interestingly, at pH 5.8, the contact angles exceeded 90° when the surfaces were annealed in an air atmosphere at temperatures of 100°C and 150°C and then allowed to return to room temperature, indicating the formation of hydrophobic surfaces. At pH 6.0, hydrophobicity was realized under annealing temperatures of 100°C, 150°C, and 200°C. XRD crystallographic analysis supported the formation of Cu2O with a cubic structure, while SEM details gave the surface morphology of the films. It serves as a very strong demonstration of the high degree of intercorrelation between wettability, pH, and annealing temperature in cost-effective routes toward hydrophobic n-Cu2O surfaces. By varying the pH and annealing temperature, it was possible to obtain both hydrophobic and non-hydrophobic surfaces. Knowing the wetting properties of n-type cuprous oxide facilitates many applications, such as the control of corrosion in coating technology and atmospheric water harvesting.
Electrodeposited p-type copper oxide for lithium-ion battery applications
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Millamadiththa, S. V.; Jayathilaka, K. M. D. C.; Wijesundara, L. B. D. R. P.
Lithium-ion batteries (LIBs) are considered a promising energy storage device due to their energy density, capacity, and longevity. In recent years, transition metal oxides have gained greater attraction due to their high theoretical capacity for rechargeable battery applications. The development of the anode and cathode in rechargeable batteries is crucial for enhancing overall battery performance. Among the different types of alternative anode materials for LIBs, Cu₂O is crucial due to its high specific capacity, low cost, environmental benefits, and ease of production. In this investigation, growth and characterization of p-Copper Oxide were carried out for possible anode material for rechargeable battery applications. Electrodeposition of p-Copper Oxide was carried out potentiostatically in a threeelectrode electrochemical cell containing 3M lactic acid 0.04M cupric sulfate (CuSO4) and 3M sodium hydroxide (NaOH) at - 450 mV vs Ag/AgCl for 30 min. The pH of the bath was adjusted to 12.5 using sodium hydroxide and bath temperature and stirring speed were maintained at 60°C and 200 rev./min respectively during the deposition. Titanium plate, Ag/AgCl, and platinum plate were used as working electrode, reference electrode, and counter electrode respectively. Grown materials were characterized using High Energy X-ray Diffraction (HEXRD), FTIR, Scanning Electron Microscopy (SEMs), MottSchottky measurements, and charge-discharge measurements. The HEXRD spectrum exhibited all the peaks corresponding to the reflection from Cu2O and CuO. Thus, HEXRD results revealed that the grown thin films (≈1 µm) consist of polycrystalline Cu2O with a cubic crystal structure and CuO with a monoclinic crystal structure indicating the formation of copper oxide. The FTIR spectra exhibited peaks related to Cu-O stretching vibrations and -OH groups, confirming the growth of Cu2O having proper composition. The SEM analysis confirmed the formation of uniform polycrystalline cubic grain morphology Cu2O having grain size in the order of 100-300 nm. Mott-Schottky analysis confirmed the p-type conductivity of Cu₂O having a doping density around 3.30×1016 cm⁻³ which is crucial for efficient conversion reactions during battery operation. The fabricated device using p-Copper Oxide as anode material exhibited a specific capacity of 205.4 mAh g-1. Overall results of this study reveal that electrodeposited p-Copper Oxide improves the interfacial properties between the anode and current collector and electrolyte. In conclusion, electrodeposited p-Copper Oxide can be used as a promising anode material for high-performance LIBs.
Fabrication and characterization of sulfur-treated cuprous oxide-based supercapacitors
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Wijesinghe, W. A. N. D.; Jayathilaka, K. M. D. C.; Ranaweera, A. L. A. K.; Wijesundara, L. B. D. R. P.; Kalingamudali, S. R. D.
Supercapacitors are crucial for modern energy storage, offering high power density, fast charging, and life spans. They are widely used in various applications, meeting the need for lightweight, flexible, and eco-friendly energy solutions. Cuprous oxide (Cu2O) holds significant promise as an electrode material for supercapacitors owing to its distinctive properties. However, electrodeposited Cu2O films often have high resistivity and surface defects, hampering their electrochemical performance. To address this issue, sulfur treatment was employed to modify the surface properties of Cu2O electrodes, aiming to enhance their electrochemical performance. In this research, sulfur-treated Cuprous-oxide thin films were used as the supercapacitor electrodes, and PVA-KOH gel polymer was employed as the supercapacitor separator and electrolyte. The Cu2O films were synthesised on a Ti substrate via electrodeposition, followed by Ammonium Sulfide (NH4)2S vapour treatment for surface modification, with varying exposure times. Untreated Cu2O thin films were analysed for comparison. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were used to examine their structural and surface morphological characteristics. The XRD analysis showed that the Cu2O deposited on the Ti substrate treated with (NH4)2S vapour did not yield distinct CuxS peaks, indicating the formation of a very thin or amorphous CuxS layer on the film surface. SEM revealed an altered morphology of the electrodeposited Cu2O thin films after the (NH4)2S vapour treatment, with the development of a non-uniform additional layer on the surface. The electrochemical performance of sulfur-treated Cu2O electrodes for supercapacitors was studied using Cyclic Voltammetry (CV), Galvanostatic Charge/Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS). Sulfur-treated electrodes exhibited enhanced performance, showing higher specific capacitance, energy density, and power density compared to untreated electrodes. The supercapacitor utilising sulfur-treated Cu2O deposited on the Ti electrodes, treated for 10 s, demonstrated superior performance with a specific capacitance of 773.81 mF/g, energy density of 154.76 mWh/kg, and power density of 111.43 W/kg. Conversely, the untreated electrode-based supercapacitor exhibited lower values, with a specific capacitance of 23.34 mF/g, energy density of 4.67 mWh/kg, and power density of 3.38 W/kg. In summary, this study explored the impact of sulfur treatment on the electrochemical performance of electrodeposited Cu2O. CV, GCD, and EIS analyses revealed improved electrochemical performance due to the reduction of surface defects with (NH4)2S surface treatment. The results indicated that the best performance can be obtained in Cu2O with a 10 s (NH4)2S exposure duration for application in supercapacitors.
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.
Development of tin oxide/copper(I) oxide heterojunction solar cell
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Balasuriya, B. M. U. H.; Kafi, F. S. B.; Jayathilaka, K. M. D. C.; Wijesundera, L. B. D. R. P.
The rapid expansion of the global population together with industrialization intensifies our diurnal energy need. Addressing the present energy demand is a challenging task. Solar energy stands as a pivotal solution to the global energy crisis, offering a sustainable and renewable energy source to meet the escalating demand for electricity. Photovoltaic energy emerges as a favorable substitute due to its widespread availability, free accessibility, eco-friendly nature, and reduced operational and maintenance expenses. However, the markedly available photovoltaics are unaffordable to the public due to their expensiveness. Accordingly, this study focuses on the development of a low-cost ecofriendly tin oxide (SnO2)-based heterojunction solar cell, aiming to enhance photovoltaic performance through systematic fabrication and optimization processes. The Cu/n-SnO2/p-Cu2O/Au heterojunction solar cell was fabricated using the method of electrodeposition. Tin (IV) Oxide (SnO₂) was employed as the n-type material and Copper(I) Oxide (Cu2O) as the p-type material. The fabrication process involved the electrodeposition of n-type SnO2 thin film on copper (Cu) substrates, followed by subsequent deposition of p-type copper(I) oxide (Cu2O) thin film. For making front contacts to the heterojunction, thin Au spots (area ∼2 × 2 mm2 ) were sputtered onto the p-Cu2O thin film of the bilayer. The back contact of the solar cell was the Cu substrate. The photoresponses of the Cu/n-SnO2/pCu2O/Au solar cell structure were monitored by optimizing the bath temperature of the SnO2 film deposition bath. Electrodeposition of SnO2 layers was performed on copper substrates in a threeelectrode electrochemical cell using a solution containing 30 mM SnCl2 and 150 mM HNO3 and electrodeposition was conducted at -0.85 V vs. Ag/AgCl for 2 min at temperature values of 70 ◦C, 75 ◦C, 80 ◦C, 85 ◦C, and 90 ◦C. To fabricate the device a p-Cu2O thin film was electrodeposited on Cu/nSnO2 film at -0.45 V vs. Ag/AgCl for 40 min in a three-electrode electrochemical cell containing 0.1 M CuSO4, 3 M C3H6O3, and NaOH aqueous solution. The temperature and pH of the bath were maintained at 60 °C and 13 respectively. The results of photoresponse measurements together with current-voltage measurements were used to optimize the solar cell. The highest photoresponses resulted for the SnO2 thin films deposited at a bath temperature value of 85 ◦C. This research contributes to the advancement of tin oxide-based heterojunction solar cell technology and offers insights for future optimization and development efforts in renewable energy generation.
Design and characterization of a tunable metamaterial absorber for efficient RF energy harvesting in the Wi-Fi frequency band
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Sahasrika, S. L. S. D.; Ranaweera, A. L. A. K.; Seneviratne, J. A.; Jayathilaka, K. M. D. C.
The pursuit of miniaturization and connectivity in semiconductor technology has led to the development of compact, interconnected devices. However, the reliance on batteries for power presents limitations. Ambient energy harvesting, particularly from radio frequency (RF) waves, offers a promising solution. This study explores the feasibility of wireless energy harvesting, especially in the context of the saturated frequency spectrum due to wireless communications. Building upon recent advancements in metamaterial technology, this study focuses on the design, fabrication, and characterization of a tunable metamaterial absorber unit cell for efficient RF energy harvesting. The aim is to exploit metamaterials, specifically tunable metamaterial absorbers (MMA), to harvest RF energy, particularly in the widely utilized Wi-Fi frequency band. To design a novel unit cell structure, simulations were conducted using the commercially available EM simulation tool CST Microwave Studio software. A novel MMA unit cell consisting of E-shaped split ring resonators, copper reflector, and FR-4 substrate layer in the middle was designed and simulated. Results demonstrated its RF energy harnessing ability, achieving peak absorptivity of 98% of incident RF energy at 2.4 GHz. The designed unit cell was fabricated using the standard PCB fabrication method. Experimental results were obtained using a network analyzer through non-contact measurement method. Results closely mirrored the simulation results, confirming a high absorptivity of 99% at 1.44 GHz. To achieve frequency tunability, an external capacitor switching circuit was integrated into the MMA unit cell. Simulation and experimental results were obtained confirming its frequency tunability. The proposed tunable metamaterial absorber unit cell offers advantages over conventional RF energy harvesting systems, including ease of implementation, a wider range of RF energy absorption, and cost-effectiveness paving the way for integration into various applications. In conclusion, this study contributes to the development of energy harvesting technologies by leveraging tunable MMA to harness ambient RF energy.
Optimization of growth parameters of electrodeposited tin oxide thin films for PV Applications
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Kafi, F. S. B.; Gunaratne, B. H.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.
Tin oxide (SnO2) is a promising photoactive semiconducting material due to its optoelectronics properties. Even though, growth of SnO2 using the method of electrodeposition is advantageous, it has paved low attention among semiconductor researchers. In this study, well-adhered photoactive SnO2 thin film was successfully electrodeposited on Cu substrates. The growth parameters, such as film deposition potential, bath temperature, and duration of deposition were optimized. Electrodeposition of SnO2 layers was performed on copper substrates in a threeelectrode electrochemical cell using a solution containing 30 mM SnCl2 and 150 mM HNO3 at a deposition potential of -0.85 V vs. Ag/AgCl. The fabricated best thin film resulted JSC value of 410 �A cm-2 and VOC value of 113 mV in 0.1 M NaNO3 electrolyte. The best thin film obtained at a bath temperature of 85◦ C for a deposition time of 120 seconds. The Mott-Schottky analysis revealed that the fabricated SnO2 thin film exhibits n-type conductivity, and it has a flat band potential of -0.51 V vs. Ag/AgCl.
Unlocking the potential of convolutional neural networks for precise classification of finger pulse waves in diabetic patients and healthy individuals
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Gunathilaka, P. A. D. H. J.; Kumarika, B. M. T.; Jayathilaka, K. M. D. C.; Perera, D.; Liyanage, J.A.; Kalingamudali, S. R. D.
Pulse wave analysis (PWA) is a valuable technique for assessing the cardiovascular health of diabetic patients. However, it encounters several challenges, including the complexity of pulse wave signals and the need for standardization and validation of measurement methods. Convolutional Neural Networks (CNNs) play a crucial role in addressing these challenges by offering a robust and accurate approach to classifying pulse wave images. Pulse wave analysis offers a cost-effective, time-efficient, highly accurate, and non-invasive method for diagnosing diabetes-related cardiovascular issues. This study aims to investigate the effectiveness of CNN in classifying finger pulse wave images to accurately distinguish between diabetic and non-diabetic subjects, thus enabling non-invasive diabetes diagnosis. The study's methodology comprises four main steps: data collection, data preprocessing, CNN model development, and model evaluation. Primary data, including finger pulse waves, blood pressure, mean arterial pressure, oxygen saturation, and pulse rate, were acquired from the multipara patient monitor. Subsequently, single pulse wave cycles from 50 healthy individuals and 50 diabetes patients were subjected to preprocessing. The CNN model was developed through data collection, preprocessing, and the creation of its architecture, followed by compilation, training, and evaluation, ultimately achieving a 92% accuracy in classifying pulse wave images for non-invasive diabetes diagnosis. Descriptive statistics were used to summarize participants' demographic and clinical data, revealing no significant differences in age, gender, or body mass index between the two groups. The model's ability to discriminate based on pulse wave images highlights its potential for noninvasive diabetes diagnosis. In order to improve accuracy in future work, increasing the dataset size and conducting hyperparameter tuning will be essential for optimizing the CNN model.

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