ICAPS-2021
Permanent URI for this collectionhttp://repository.kln.ac.lk/handle/123456789/23880
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Item 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.Item 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.Item 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.Item 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.