Browsing by Author "Wijesundera, R. P."

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A Comparative Study: Sequential and Single-Step-Electrodeposited CZTS Thin Films
(Physica Status Solidi, 2022) Fernando, W. T. R. S.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.; Siripala, W.
CZTS (Cu2ZnSnS4) is a relatively new and promising semiconductor material suitable for photovoltaic applications due to its favorable optoelectronic properties. Of the many techniques available for growing these films, a comparative study on sequential and single-step electrodeposition methods to grow CZTS films is carried out in this investigation to explore the possibility of improving the quality of the films using the inexpensive electrodeposition technique. Mainly in both methods, potentiostatic electrodeposition technique is adopted for growing CZTS thin films. In both methods, growth conditions of the CZTS films are optimized after measuring the photoresponses in a photoelectrochemical (PEC) cell of the films that resulted at the end of each deposition step. The observed structural and optoelectronic properties of the films reveal that, in general, structurally good and photoactive CZTS films can be prepared using both methods. Moreover, photoresponse and Mott–Schottky measurements on CZTS films in a PEC reveal that CZTS films prepared using the single-step electrodeposition have better photoactive properties and improved doping densities. This important finding shows that when developing CZTS-based solar cells using the inexpensive electrodeposition technique, single-step electrodeposition is more advantageous.
Cu2O Homojunction Solar Cells: Efficiency Enhancement with a High Short Circuit Current
(2024) Thejasiri, S. A. A. B.; Jayathilaka, K. M. D. C.; Kafi, F. S. B.; Kumara, L. S. R.; Seo, O.; Yasuno, S.; Sakata, O.; Siripala, W.; Wijesundera, R. P.
Cu2O homojunction solar cells were fabricated using potentiostatic electrodeposition technique. n-Cu2O thin films were grown in an acetate bath while p-Cu2O thin films were grown in a lactate bath. In the growth of n-Cu2O films, cupric acetate concentration, pH and temperature of the bath, deposition potential and duration (film thickness) and annealing temperature were investigated. In the growth of p-Cu2O on n-Cu2O, concentration of copper sulphate and lactic acid solutions, pH and temperature of the bath, deposition potential and duration were investigated. In addition, the procedure of sulfidation of p-Cu2O film surface using (NH4)2S vapor, before depositing Au front contact, was also optimized to enhance the photoactive performance. The structural, morphological and optoelectronic properties of the Cu2O films were investigated using scanning electron microscopy (SEMs), high energy X-ray diffraction (HEXRD), hard X-ray photoelectron spectroscopy (HAXPES), spectral response and current–voltage (J-V) measurements. The best Cu2O homojunction solar cell exhibited Voc = 460 mV, Jsc = 12.99 mA·cm−2, FF = 42% and η = 2.51%, under AM 1.5 illumination. Efficiency enhancement with the record high Jsc value for the Cu2O homojunction solar cell has mainly been due to the optimization of pH of the n-Cu2O deposition bath and lactic acid concentration of the p-Cu2O deposition bath.
Effect of annealing temperature on the wetting properties of electrodeposited Cu2O
(Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Shakya, M. D. P. A.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.; Wanninayake, W. T. M. P. K.
Surface wettability is one of the important physical parameters, which manifests the affinity of a liquid towards a solid phase. In recent years, controlling the wettability of solid surfaces has drawn significant attention due to its influence in wide range of applications. Cuprous Oxide (Cu2O) is well known as a technologically important material for various fields due to its unique advantages such as low cost, high chemical stability and remarkable electrochemical performance. This work examines the impact of the post annealing temperature on the wetting ability of Cu2O thin films. A set of Cu2O thin films was deposited on Ti substrate at a deposition potential of -200 mV vs saturated calomel electrode (SCE) in an acetate bath containing an aqueous solution of 0.1 M sodium acetate and 0.01M cupric acetate at bath temperature of 60 ºC and pH value of 6.5 for 45 min. Potentiostatic electrodeposited Cu2O films were annealed in air at 100 °C, 150 °C, 200 °C, 250 °C, 350 °C and 400 °C for 20 and 40 minute separate time intervals. The surface morphological and structural characterizations of prepared samples were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. SEM (Zeiss evols 15) and SHIMADZU (XD-D1) X-ray diffractometer were used to study the samples. XRD spectral patterns indicated the presence of Cu2O without having any impurity phases. The water contact angles were measured using the sessile drop method in order to investigate the effect of temperature on the wettability of the Cu2O films. The contact angle of Cu2O thin film changed from 110o (non-wetting) to 10o (completely wetting) with the increase in the annealing temperature. The contact angle measurement for cuprous oxide showed a transition of cuprous oxide surface from hydrophobicity to hydrophilicity and the maximum hydrophobicity was observed at 150 ± 1 oC. Similar variation and maximum hydrophobicity of the contact angle were observed for both annealing durations (20, 40 minutes). SEM micrographs of electrodeposited Cu2O thin films indicated significant changes in the surface morphology with annealing temperature. Dimension of grains becomes smaller with increasing temperature. This suggests that higher heating temperatures lead to a decrement in the contact angle. Based on the results of the investigation, surface morphology is the primary determinant of the wettability qualities of Cu2O thin films.
Effect of Benzene Derivatives as Guest Molecules on Semiconductor Properties of MOF-199
(ChemistrySelect, 2021) Zahadiya, H.; Wijesundera, R. P.; Hettiarachchi, C. V.
A metal organic framework, MOF-199, has been synthesized under solvothermal conditions. Powder X-ray diffraction (PXRD) pattern, Fourier-transform infrared spectra (FT-IR) and scanning electron microscopic images (SEM) confirmed the formation of the expected MOF-199 structure. The semiconductor properties of MOF-199 were then fine-tuned by introducing three benzene derivatives as guest molecules (aniline, m-aminobenzoic acid and p-benzoquinone). Modified MOF-199 samples were characterized using PXRD and FT-IR. Mott-Schottky analysis and solid-state UV-visible spectroscopy were used to investigate the semiconductor properties of these materials. Once MOF was modified with benzene derivatives, slight changes in d spacing values of PXRD patterns and appearance of new peaks in FT-IR spectra were observed. The Mott-Schottky analysis of modified MOF-199 demonstrated an enhancement in the carrier concentration up to 83 % and a negative potential shift of the flat band potential compared to pure MOF-199, indicating a higher degree of band bending. According to the solid-state UV-visible spectra, doping with organic molecules reduced the bandgap in modified MOF-199. Thus, this study evidently showcases the potential of fine-tuning the semiconductor properties of a MOF according to the requirement that allows a single MOF to be utilized in a variety of applications with a simple modification.
Fabrication of Cu2O homojunction thin films for photovoltaic applications.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Kafi, F. S. B.; Jayathilaka, K.M.D.C.; Wijesundera, R. P.; Siripala, W.
Environmentally friendly cuprous oxide (Cu2O) is an attractive cost effective material for developing photovoltaic devices due to its astounding properties. Interestingly, the fabrication of low cost Cu2O homojunction devices is possible due to Cu2O is abundant and the ability of forming the p-Cu2O and n-Cu2O thin films using cost effective electrodeposition technique. Indeed, it is necessary to optimize p-n junction devices by varying deposition parameters. Vividly, the pH of the deposition bath controls the quality of the electrodeposited Cu2O thin films. Hence, it is important to optimize the pH value of the bath use for the electrodeposition of n-Cu2O and p-Cu2O films for developing Cu2O based devices. In this study, Cu2O thin film homojunction device was fabricated using a successive deposition of an n-Cu2O film followed by a p-Cu2O film, in two different baths; acetate and lactate respectively. The Cu2O homojunction was fabricated on a Ti substrate by the two-step potentiostatic electrodeposition process. A set of n-Cu2O thin films were electrodeposited on Ti substrate in a three electrode aqueous electrochemical cell containing 0.1 M sodium acetate and 0.01 M cupric acetate at potential of -200 mV vs. Ag/AgCl electrode, bath temperature of 55 °C and the film deposition time of 1 hour at two different pH values of n-Cu2O thin film deposition baths; 6.1 and 6.5. Then to optimize the Cu2O homojunction, Ti/n-Cu2O/p-Cu2O junction was fabricated by consequently electrodepositing p-Cu2O thin film on n-Cu2O film by changing the pH value from 7.0 to 13 of the p-Cu2O thin film deposition bath. The electrochemical bath used for the deposition of p-Cu2O thin films contained 3 M lactic acid, 0.4 M copper sulfate and 4 M NaOH. pH of the deposition baths were controlled by adding NaOH and HCl. Then Ti/n-Cu2O/p-Cu2O/Au structure was fabricated by sputtering Au on the resulted Cu2O homojunction. The highest photoactive film observed for Ti/n-Cu2O/p-Cu2O/Au structure that was fabricated at pH values of 6.1 and 11.0 for n-Cu2O and p-Cu2O deposition baths respectively. The observed VOC and JSC values for the optimum Ti/n-Cu2O/p-Cu2O/Au structure was 344 mV and 1.13 mA/cm2 respectively, under AM 1.5 illumination. The resulted high VOC and ISC values evident for the possibility of fabrication of Cu2O homojunction devices by employing consecutive electrodeposition of an n-Cu2O layer followed by a p-Cu2O layer using the relevant baths at different growth conditions. Promisingly, fabricated Cu2O homojunction may further improved by surface treatments and optimizations, to produce high efficient Cu2O homojunction devices.
Fabrication of inverted organic solar cells on stainless steel substrate with electrodeposited and spin coated ZnO buffer layers
(Journal of Polymer Engineering, 2022) Namawardana, D. G. K. K.; Wanigasekara, R. M. G.; Wanninayake, W. T. M. A. P. K.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.; Siripala, W.; Malik, M. I.
Polymer based organic solar cells (OSCs) are of tremendous interest as suitable candidates for producing clean and renewable energy in recent years. In this study, inverted OSCs on stainless steel (SS) substrate with zinc oxide (ZnO) as the electron selective transport layer (ESTL), are investigated, occupying bulk heterojunction blend of regioregular poly(3-hexylthiophene) (P3HT) and phenyl- C61-butyric acid methyl ester (PCBM) as the active material and poly-(4,3-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole transport layer (HTL). The device structure is SS/ZnO/P3HT:PCBM/PEDOT:PSS/Au. ZnO films are prepared by spin coating and electrodeposition techniques, followed by annealing under ambient conditions. The insertion of ZnO layer between the SS substrate and active layer has improved short-circuit current ( Jsc), open-circuit voltage (Voc), fill factor (FF), and power conversion efficiency (PCE) compared to those of the reference cell without ZnO layer, achieving the highest efficiency of 0.66% for the device with spin coated ZnO from sol–gel technique. This enhancement can be attributed to the effective electron extraction and the increased crystallinity of ZnO after annealing treatments at higher temperatures as further confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses.
Fabrication of natural dye sensitized solar cells with eastern black nightshade extract.
(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Kulathilaka, D. S. V.; Wanninayake, W. T. M. A. P. K.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.
Energy crisis is one of the biggest challenges for the humans in the world today. Considerable efforts have put by many researchers to tackle this issue. Solar cells represent critical role for extracting energy from the sun which is the most promising natural energy source. The dye-sensitized solar cells (DSSCs) have attracted much attention owing to their simple structure, transparency, flexibility, low production cost, and wide range of application. The function and structure of the dye-sensitized solar cells are based on the sensitization of the wide band gap semiconducting materials which are arranged as a sandwich-liked structure that consists of a photo-sensitized semiconductor formed between an anode and a cathode (an electrolyte). The essential sensitization of wide bandgap semiconductor electrodes is achieved by incorporating dye molecules in its structure. In this study, we focused on the Eastern black nightshade (Solanum ptycanthum) natural dye as the sensitizer of TiO2 photoelectrode. The power conversion efficiency of the Eastern black nightshade dye incorporated solar cells was 0.00616%. It was a clear improvement of the power conversion efficiency of the reference solar cell which was made up with the Grapes dye under the same experimental conditions. The power conversion efficiency of the reference solar cell was 0.00265%. These results reveal that the Eastern black nightshade natural dye has improved the power conversion efficiency of dye-sensitized solar cells compared to those with Grapes dye which is one of the most popular dye among the researches.
Growth and Characterization of Seed‑Assisted, EDTA‑Treated, Chemical Bath‑Deposited CdS
(Journal of Electronic Materials, 2021) Kumarage, W. G. C.; Wijesundera, R. P.; Seneviratne, V. A.; Jayalath, C. P.; Gunawardhana, N.; Kaur, N.; Comini, E.; Dassanayake, B. S.
A simple low-cost method to enhance the electrical properties including open-circuit voltage (VOC), flat-band potential (Vfb) and short-circuit current (ISC) in the photoelectrochemical (PEC) cell of cadmium sulfide (CdS) thin films is presented. The PEC cell properties were determined using the configuration Pt/0.1 M Na2S2O3/ CdS. Three different sets of CdS thin films were grown: (a) chemical bath-deposited CdS (CBD-CdS), (b) electrodeposited seed-assisted CBD-CdS (ED/CBD-CdS) and (c) ED/CBD-CdS deposited under the presence of ethylenediaminetetraacetic acid (EDTA) in a reaction solution of CBD (ED/(CBD+EDTA)-CdS). The FE-SEM images suggested the formation of clusters with spherical shape in the presence of a seed layer. All the samples grown with seed layers demonstrated improved ISC and VOC values in the PEC cell compared to the CBD-CdS films due to better contact between the substrate and CBD-CdS. Furthermore, the carrier concentration (ND) and Vfb were also found to improve due to the introduction of the seed layer. In the case of ED/(CBD+EDTA)-CdS, the cluster size was found to be smaller, giving rise to a larger effective surface area. The improved effective surface area, interparticle connections and adhesion of CdS to the FTO substrate resulted in superior electrical properties of ED/(CBD+EDTA)-CdS compared to ED/CBD-CdS and CBD-CdS films.
Growth of photoactive Cu2ZnSnS4 by single step electrodeposition
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Fernando, W. T. R. S.; Jayathileka, K. M. D. C.; Wijesundera, R. P.; Siripala, W.
Cu2ZnSnS4 (CZTS) is a promising candidate for application in low-cost and environmentally-friendly thin film solar cells due to its optoelectronics properties. It is a perfect absorber material for photovoltaic applications due to its high absorption coefficient (>10-4 cm-1) and direct optical bandgap (1.4 - 1.5 eV). Among the CZTS preparation techniques, single step electrodeposition is an attractive because of its simplicity, low cost and easy to control stoichiometry. In this study, CZTS thin films on Mo substrate were potentiostatically electrodeposited in a three electrode electrochemical cell containing 0.02 M copper (II) sulfate pentahydrate (CuSO4·5H2O), 0.01 M zinc sulfate heptahydrate (ZnSO4·7H2O), 0.02 M tin sulfate (SnSO4) and 0.02 M sodium thiosulfate (Na2S2O3) at room temperature. 0.2 M tri-sodium citrate (C6H5Na3O7:Na3-citrate) was used as complexing agent and tartaric acid (C4H6O6) was used as pH control solution. pH of the bath was maintained at 5.0 Ag/AgCl and platinum electrodes were used as reference and counter electrodes respectively. Mo substrate with a deposition area of 1×2 cm2 was used as the working electrode. Electrodeposition was carried out at -1.05 V vs Ag/AgCl using a Hokuto Denko model HZ-5000 Potentiostat/Galvanostat. CZTS samples were prepared using different deposition durations (5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 min). Optimum bath conditions were explored using cyclic voltammetry. Samples were characterized using XRD, optical absorption, dark and light I-V measurements and spectral response measurements in a PEC containing 0.1 M sodium acetate. XRD measurements evidenced that the formation of single phase polycrystalline CZTS. Reflectance measurements has revealed that the band gap energy of the films is 1.5 eV and I-V measurements revealed that CZTS thin films were photoactive and p-type. To enhance the photoactive properties films were annealed at different temperatures (500, 550, 6000C) and durations (15, 30, 45 min) in H2S surrounding. As the results, photoactive performance of the films enhance with the annealing treatment in H2S. In conclusion, it can be mentioned that the highest photoactive p-CZTS thin films can be grown by annealing the 40 min deposited samples at 5500C for 30 min in H2S. The methodology developed in this study will be further investigated, in order to develop the material for wider applications.
Molecular tailoring of donor and acceptor materials of organic solar cells for improvement of their optoelectronic properties
(Materials Science in Semiconductor Processing, 2022) Ansari, M. A.; Hafeez, A.; Mustafa, M.; Wijesundera, R. P.; Malik, M. I.
Improvement in the efficiency of organic solar cell (OSC) is one of the hot topics of the modern-day research. Despite environment friendliness and several other practical advantages, the power conversion efficiency (PCE) of OSC has not yet achieved the levels of the commercial inorganic solar cells. In this context, molecular tailoring of the donor and acceptor materials can help in alignment of the energy levels in order to improve PCE. In this study, we demonstrate the introduction of different functional groups on the most widely used donor and acceptor materials namely poly(3-hexylthiophene) (P3HT) and fullerene, respectively. P3HT was successfully converted into poly(4-bromo-3-hexylthiophene), poly(4-chloro-3-hexylthiophene), and poly(3-hexyl-4-nitrothiophene) through bromination, chlorination, and nitration reactions, respectively. Similarly, fullerene was converted into phenyl-C61-pentanoic acid methyl ester, phenyl-C61-pentanoic acid, and methyl-2-C61 propionate. The success of different modifications on P3HT and fullerene was monitored by 1H NMR spectroscopy. Finally, the optoelectronic properties after the above-mentioned modifications were evaluated by UV–Vis spectroscopy and cyclic voltammetry.
A new Sodium based electrolyte – PEO10NaBrO3
(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Sankalpa, H. A. C.; Sumathipala, H. H.; Wijesundera, R. P.
The necessity of new and environmental friendly rechargeable batteries is increasing day by day due to the current technology development and power demand. Hence, efficient and low-cost new electrolyte materials have to be discovered and more attention has to be placed on searching environmental friendly, non-toxic materials. Sodium salts are the most potential materials due to their abundance and low-cost. This study focuses to investigate the electrical conductivity of a sodium-based electrolyte which can be used in solid state batteries. Composite of Poly Ethylene Oxide (PEO) and Sodium Bromate (NaBrO3) are used as the electrolyte and samples were prepared by the hot-pressed method. Electrical conductivity measurements were carried out for samples prepared by varying the molar ratio of PEO and NaBrO3. According to the results, PEO-NaBrO3 has the potential to be developed as a sodium-based electrolyte. Experimental results revealed that the highest electrical conductivity is being produced for PEO10NaBrO3 samples. Best sample exhibited 3.44×10-5 S cm-1 conductivity in room temperature (30 °C) and 2.14×10-2 S cm-1 conductivity at 100 °C. These results show the evidence of potential usage of PEO10NaBrO3 as an electrolyte in solid state Batteries. However, further investigations should be carried out to investigate the contribution of the Sodium ions for the observed conductivity
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.
Optimization of growth parameters of photoactive Cu2ZnSnS4.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Fernando, W. T. R. S.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.; Siripala, W.
Cu2ZnSnS4 (CZTS) is a promising candidate for application in low-cost and environmentally friendly thin film solar cells due to its optoelectronics properties. It is a perfect absorber material for photovoltaic applications due to its high absorption coefficient (>10-4 cm-1) and direct optical band gap (1.4 - 1.5 eV). Among the CZTS preparation techniques, electrodeposition of Cu, Sn and Zn stack layers followed by sulphurisation in H2S is an attractive technique because of its simplicity, low cost and easy to control stoichiometry. In this investigation, optimization of growth parameters in order to obtain photoactive CZTS thin films by sulphurisation of electrodeposited Cu, Sn and Zn stack layers has been investigated. Cu thin film was electrodeposited on Mo substrate at –0.89 V Vs Ag/AgCl electrode in an electrochemical cell containing 0.4 M CuSO4, 3 M lactic acid and NaOH at pH 11. Deposition of Sn thin film on Mo/Cu electrode was carried out at -1.2 V Vs Ag/AgCl in an electrochemical cell containing 0.055 M, 2.25 M NaOH and 8 ml of sorbitol. Zn thin film was electrodeposited on Mo/Cu/Sn at -1.2 V Vs Ag/AgCl in an electrochemical cell containing 0.2 M ZnSO4. Deposition parameters of Cu, Sn and Zn have been obtained by voltammograms. In order to grow CZTS, Mo/Cu/Sn/Zn thin film electrodes were annealed at 550 oC for 60 min in H2S. Sulphurisation process was carried out at different temperatures and durations using set of identical Mo/Cu/Sn/Zn thin film electrodes and thereby optimized temperature and duration of the sulpurisation. Atomic ratios of initial Cu, Sn and Zn layers could be crucial parameters in determining properties of CZTS thin films. Therefore, atomic ratios of Cu/Sn/Zn layers were optimized by changing Cu, Sn and Zn deposition duration. Various combinations of deposition durations were carried out and optimized by monitoring the dark and light I-V measurements in a PEC containing 0.1 M sodium acetate. Dark and light I-V characteristics revealed that the best photoactive CZTS films can be grown by depositing Cu for 20 min, Sn for 10 sec and Zn for 10 sec. Results further showed that photoconductivity of CZTS thin films is p-type. It is evident from reflectance measurements that the band gap of the CZTS films is 1.5 eV. In conclusion, it is found that the highest photoactive p-CZTS thin films can be grown by sulphurisation of electrodeposited Cu, Sn and Zn stack layers on Mo substrate using H2S at 550 oC for 60 min. Cu: Sn: Zn ratios of the stack layers are the crucial parameters in determining photoactive CZTS thin films. The methodology developed in this study will be further investigated in order to develop the materials for wider applications.
Photocurrent improvement in grape dye sensitized solar cells by in cooperation of electrodeposited Cu particles in TiO2 photoanode
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Shakya, M. D. P. A.; Jayathilaka, K. M. D. C.; Wanninayake, W. T. M. P. K.; Kumara, R.; Siripala, W. P.; Wijesundera, R. P.
A worldwide effort is currently underway to address the world's energy crisis by finding sustainable energy alternatives. The Dye-Sensitized Solar Cell (DSSC) is a type of solar cell device that functions based on electrochemical principles and uses light sensitive dyes within its TiO2 photoelectrode layer to absorb light. The DSSC, one of the potential solutions, appears to be the most viable option for a future renewable energy source due to its sustainability and environmental friendliness. In cooperation of metal particles like Au or Ag in nano scale to the photoanode is one of the promising methods to improve the efficiencies of these DSSCs. Among these metal particles Cu has some distinct properties such as abundance, low toxicity, low cost and it undergoes Localized Surface Plasmonic Resonance (LSPR) effect like Au nanoparticles. Therefore, to improve the DSSC performances, in this study, Cu particle incorporation to the TiO2 electrode was carried out by electrochemical deposition method. Homogeneous TiO2 paste prepared by mixing appropriate amount of TiO2 powder (Titanium (IV) dioxide), ethanol, and acetic acid was deposited on a transparent Indium-doped Tin Oxide (ITO) conductive glass substrate by doctor blading method. Electrodeposition of Cu particles were potentiaostatically grown in the TiO2 electrode at -700 mV vs Ag/AgCl reference electrode using a three electrode electrochemical cell configuration with Pt as the counter electrode and 0.1 M sodium acetate and 0.01 M cupric acetate electrolyte at room temperature. Natural dye grapes have been used as sensitizer in the study. DSSCs were fabricated by sandwiching above TiO2 films with a C coated counted electrode using KI/I2 based electrolyte. The devices were characterized by analysing the UV – vis absorbance spectra and current density-voltage (J-V) curves and controlled potential coulometry measurements. The UV – vis absorbance spectrum revealed that the light absorption of DSSCs enhanced due to the incorporation Cu. The power conversion efficiency of 0.10%, photocurrent density (JSC) of 501 μA/cm2, open circuit voltage (VOC) of 0.47 V, and fill factor (FF) of 42% were achieved after the Cu incorporation in the photoanode. It is found that due to the incorporation of Cu particles, a slight voltage drop was visible, but there was a significant increase in the photocurrent density (JSC) from 308 μA/cm2 to 501 μA/cm2. The efficiency also increased from 0.07 to 0.10%. DSSC with the incorporated Cu particles showed 62% enhancement in the photocurrent compared to the DSSC without Cu particles.
Photoelectrolysis of water using electrodeposited Cu2O electrodes.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Silva, A. G. T. D.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.; Siripala, W.
At present, fossil fuels are the main energy contributor of the world’s energy needs but gradually depletion of fossil fuels is heading towards an energy crisis. Therefore it is very important for us to find out a renewable clean energy source to minimize the use of fossil fuels and environmental problems created by the burning fossil fuels. Among the suggested alternative fuels, hydrogen is one of the best and it can be produced by photoelectrolysis of water. Finding correct semiconducting materials and techniques are the key areas of research in the development of an efficient photoelectrolysis device. Ultra low cost electrodeposited cuprous oxide (Cu2O) is a good candidate material because it has required semiconductor properties for the process. p-Cu2O electrode electrolyte system requires external bias to produce photocurrent and this can be overcome by using n-Cu2O. However, in our previous studies, we have observed the possibility of enhancement of photocurrent at zero bias using double electrode system (electrodeposted n-Cu2O, thermally grown p-Cu2O, electrolyte system). In this investigation it was studied the possibility of photoelectrolysis of water using electrodeposited n- and p-Cu2O thin film electrodes as a double photoelectrode system in a 0.1 M sodium acetate photoelectrochemcal cell. n-Cu2O thin films on Ti substrates were potentiostatically electrodeposited at −200 mV Vs Ag/AgCl for 60 minutes in an aqueous solution containing 0.1 M sodium acetate and 0.01 M cupric acetate. The initial pH of the deposition bath was adjusted to 6.1. The temperature of the electrolyte was maintained at 55 °C and counter and reference electrodes were a platinum plate and a Ag/AgCl electrode, respectively. p-Cu2O thin films were electrodeposited on Ti substrate at -400 mV Vs Ag/AgCl for 40 min in a three-electrode electrochemical cell containing a 3 M sodium lactate and 0.4 M CuSO4 solution at pH 11. During the electrodeposition, the baths were continuously stirred using a magnetic stirrer. Prior to the film deposition, substrates were cleaned with detergent, dilute HCl, distilled water, and finally ultrasonicated in distilled water. Electrolytic solutions were prepared with distilled water and reagent-grade chemicals. n-Cu2O thin films are annealed at 150 oC for 10 min in air. Possibility of photoelectolysis using electrodeposited Cu2O has been investigated using dark and light current–voltage measurements in a three-electrode electrochemical cell containing 0.1 M aqueous sodium acetate solution. Results reveal that photoelectrolysis process is enhanced by 380% when n- and p-Cu2O double electrode system was operated compared to the n-Cu2O single electrode system.
Stability of the performance of inverted P3HT/PCBM based organic solar cells
(Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Weerasinghe, M. L. A.; Wanninayake, W. T. M. A. P. K.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.
The organic solar cell extracts and converts solar energy to electricity without environmental hazardous including global warming. Bulk heterojunction (BHJ) structure of the organic solar cells (OSCs) have higher performance than the layered structure. But the main disadvantage of the OSCs is the poor stability of the device. Therefore, this study was focused on the stability of fabricated P3HT/PCBM OSCs. A series of inverted organic solar cells were fabricated on titanium substrate using spin coated P3HT/PCBM, doctor bladed PEDOT: PSS and sputter coated Au. Device characterizations were carried out under AM 1.5 illumination during 20 days. Electrical parameters of open-circuit voltage (VOC), short circuit current density (JSC), fill factor (FF) and power conversion efficiency (PCE) were obtained during 20 days from dark and light I-V measurements. Best device produced VOC of 282 mV, JSC of 2.65 mAcm-2, FF of 0.21 and PCE of 0.15%. The PCE decreased dramatically and became almost constant value of 0.04% within 20 days. FF was constant throughout the 20 days and VOC decreased slightly within 20 days. However, JSC of the device decay from 2.65 mA/cm2 to 1.0 mA/cm2 within the considered time duration. Hence, this PCE behavior of the device is due to the loss of JSC. PCE of the organic solar cell is not higher than the silicon solar cell, but it can be improved by changing the geometry of the solar cell, annealing conditions, etc. This instability of the device upon irradiation is due to photochemical and photophysical degradation in the active layer, and the active layer/electrode interface. Further, low JSC is mainly due to the low electron mobility and low exciton diffusion length. Performance of the device can be improved carefully controlling the device fabrication parameters in the inert gas surrounding.
Thin film cuprous oxide homojunction photoelectrode for water splitting
(Faculty of Science, University of Kelaniya, Sri Lanka., 2021) Kafi, F. S. B.; Thejasiri, S. A. A. B.; Wijesundera, R. P.; Siripala, W.
Employing cuprous oxide (Cu2O) photoelectrodes in photoelectrochemical cells to generate hydrogen by water splitting is beneficial. Conventionally, it is limited in practice because of the well-known reasons of its inherent corrosiveness and poor conversion efficiencies. In this study, we have investigated the possibility of improving the efficiency of Cu2O photoelectrode in the form of p-n homojunction together with sulphidation. Initially, the optimum pH values for the n- and p-Cu2O thin film deposition baths are determined as 6.1 and 13 for Ti/n-Cu2O/p-Cu2O in photoelectrochemical cell configuration. Then, at these pH values the duration of n- and p-Cu2O thin film deposition is optimized by forming Ti/n-Cu2O/p-Cu2O photoelectrode. In this study, we found that at 45 minutes of n-Cu2O and 50 minutes of p-Cu2O thin film deposition together with sulphidation forms relatively high efficient Ti/n-Cu2O/p-Cu2O photoelectrode resulting Solar-To- Hydrogen (STH) conversion efficiency of 0.9%. In addition, current-voltage characteristic of the best Cu2O homojunction photoelectrode exhibits more negative shift in onset of photocurrent which indicates that photocurrent generation and transportation have improved by the formation of homojunction and further been enhanced by sulphidation.
Use of cuprous oxide thin film semiconductors for dissolved oxygen sensing: A preliminary study
(Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Wijesooriya, H. E.; Seneviratne, J. A.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.
Monitoring and maintaining the quality of water is extremely important as it can severely affect the health of humans as well as animals. Dissolved oxygen is one of the key indications of water quality. Cuprous Oxide (Cu2O) semiconductor material is an ultra-low cost, environmentally friendly, earth abundant material which is considered as a green alternative to many sensing applications. Therefore, Cu2O thin film semiconductors could potentially act as a dissolved oxygen sensor due to their unique electrical features. Generally, a significant change in the electrical conductivity is caused by the adsorption of molecules on the surface of Cu2O semiconductor material. In this investigation, the possibility of sensing dissolved oxygen using Cu2O thin film semiconductors was explored. Cu2O thin films were grown using the electrodeposition technique on titanium (Ti) substrates at -200 mV vs Ag/AgCl for 60 minutes in an electrochemical cell containing an acetate bath of 0.1 M sodium acetate and 0.01 M cupric acetate. The temperature of the bath was maintained at 55 ℃ and stirred at a speed of 50 rev/min. The Ag/AgCl electrode was used as the reference electrode, while the platinum electrode was the counter electrode. Prepared Cu2O thin films were characterized in two-electrode systems using resistance measurements at ambient conditions in two different Deionized (DI) water volumes of 100 ml and 200 ml while aerating oxygen at a constant rate at the room temperature. Significant linear change in resistance was observed with increasing dissolved oxygen concentration under ambient condition in both cases. In comparison with experiment carried out with 100 ml of DI water volume, it was observed that in 200 ml DI water volume it takes more than twice the time to saturate with oxygen. Furthermore, it was observed that the constant resistance value of the system at the saturation of 200 ml DI water volume was higher than the constant resistance obtained at the saturation of 100 ml DI water volume. This preliminary investigation revealed that Cu2O thin films could use to monitor dissolved oxygen. However, further investigations need to be performed to optimize the dissolved oxygen sensing property of Cu2O thin films.