Browsing by Author "Kafi, F.S.B."

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Effect of pre-surface treatments on p-Cu2O/Au Schottky junctions
(Journal of the National Science Foundation of Sri Lanka,, 2021) Kafi, F.S.B.; Jayathilaka, K.M.D.C.; Wijesundera, R.P.; Siripala, W.
Cuprous oxide (Cu2O) is a suitable semiconducting material in fabrication for low-cost, eco-friendly semiconductor junction devices. Besides the parameterization of the growth conditions of Cu2O, formation of metal contacts impact the overall performance of these type of devices. The existence of unavoidable dangling bonds and/or dislocated surface atoms could lead to form imperfect contacts with metals, for example in Cu2O/Au junction devices. Nevertheless, modification of the Cu2O thin film surfaces prior to make contacts with Au has shown the capability to alter the junction properties. Here we report that, the application of surface treatments; annealing and/or sulphidation on specifically the electrodeposited p-Cu2O thin film surfaces, where p-Cu2O thin films were grown in low cupric ion concentrated acetate bath, has influenced the interfacial properties of particular p-Cu2O/Au Schottky junctions compared to the untreated p-Cu2O/Au Schottky junction. This has been well-established by the results of SEM and C-V characterizations of p-Cu2O/Au Schottky junctions. The subsequent annealing and sulphidation of p-Cu2O thin film surfaces have lowered the built-in potential value by 121 mV compared to the untreated Schottky junction. This result reveals the possibility of employing surface treatments on electrodeposited Cu2O thin films in fabrication of high efficient Cu2O based junction devices.
Effect of pre-surface treatments on p-Cu2O/Au Schottky junctions
(Journal of the National Science Foundation of Sri Lanka, 2021) Kafi, F.S.B.; Jayathilaka, K.M.D.C.; Wijesundera, R.P.; Siripala, W.
Cuprous oxide (Cu2O) is a suitable semiconducting material in fabrication for low-cost, eco-friendly semiconductor junction devices. Besides the parameterization of the growth conditions of Cu2O, formation of metal contacts impact the overall performance of these type of devices. The existence of unavoidable dangling bonds and/or dislocated surface atoms could lead to form imperfect contacts with metals, for example in Cu2O/Au junction devices. Nevertheless, modification of the Cu2O thin film surfaces prior to make contacts with Au has shown the capability to alter the junction properties. Here we report that, the application of surface treatments; annealing and/or sulphidation on specifically the electrodeposited p-Cu2O thin film surfaces, where p-Cu2O thin films were grown in low cupric ion concentrated acetate bath, has influenced the interfacial properties of particular p-Cu2O/Au Schottky junctions compared to the untreated p-Cu2O/Au Schottky junction. This has been well-established by the results of SEM and C-V characterizations of p-Cu2O/Au Schottky junctions. The subsequent annealing and sulphidation of p-Cu2O thin film surfaces have lowered the built-in potential value by 121 mV compared to the untreated Schottky junction. This result reveals the possibility of employing surface treatments on electrodeposited Cu2O thin films in fabrication of high efficient Cu2O based junction devices.
Electrodeposited thin film SnO2 photoelectrode for PEC applications
(Institute of Physics, Sri Lanka, 2024) Kafi, F.S.B.; Gunaratna, B.H.; Jayathilaka, K.M.D.C.; Wijesundera, R.P.
Tin oxide (SnO2) is a promising semiconductor material to develop photoelectrodes for photoelectrochemical (PEC) cells. Indeed, an effective PEC cell could be developed only if the photoelectrode is stable and free of corrosion in the selected electrolytic solution. In other words, the choice of an electrolyte for a PEC cell determines the stability of the photoelectrode in the PEC cell. In this study, we propose aqueous 0.1 M sodium nitrate (NaNO3) as an effective electrolyte for the PEC cell where thin film SnO2 is a photoelectrode. Current-voltage (I-V) measurements obtained by illuminated chopped ultra violate (UV) radiation established the electrodeposited thin films of SnO2 are stable and free of corrosion/photocorrosion in our PEC cell. In addition, we report the dependence of the photoresponses of electrodeposited thin film SnO2 in this PEC on the bath temperature and the deposition time.
Enhancement of photovoltaic performance of Cu2O homojunction by introducing a ZnO buffer layer
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Thejasiri, S.A.A.B.; Kafi, F.S.B.; Wijesundera, R.P.; Siripala, W.
Cuprous oxide (Cu2O) is a semiconductor material having the capability of producing a theoretical conversion efficiency of 20% which is acceptable for solar energy applications. In this investigation, we have explored the possibility of improving open circuit voltage (Voc) of Cu2O homojunctions by introducing a ZnO buffer layer in between n- and p-Cu2O layers. The thin buffer layer may be able to develop an additional potential drop across the interface improving Voc without hindering short-circuit current density (Jsc). In this investigation, n-Cu2O thin films were electrodeposited on Ti substrates at -200 mV vs Ag/AgCl for 30 minutes in an acetate bath. Samples were then annealed at 175 oC for 30 min in air. ZnO thin film was deposited on Ti/nCu2O film by employing Successive Ionic Layer Adsorption Reaction (SILAR) technique using 0.1 M Zn(NH3)4 2+ aqueous solution. Resulted samples were annealed at 175 oC for 10 minutes. pCu2O thin film was electrodeposited on Ti/n-Cu2O/ZnO electrode at -450 mV vs. Ag/AgCl for 45 minutes in a lactate bath. Surface of p-Cu2O was exposed to ammonium sulphide vapor in order to prepare an ultra-thin Cu2S layer. Finally, 2x2 mm2 Au spots were sputtered on the coper sulphide layer. A set of Ti/n-Cu2O/ZnO/p-Cu2O/Au devices having different thicknesses of ZnO layers was prepared by changing the number of successive adsorption cycles and characterized them by using dark and light current voltage measurements. Dark and light current voltage characteristics revealed that the device fabricated using 3 cycled ZnO layer produces the best photoactive performance. Without the buffer layer, the device produced Voc of 384 mV and Jsc of 8.1 mAcm-2 , under AM 1.5 illumination. With the ZnO buffer layer the device Voc improved up to 416 mV and Jsc up to 9.1 mAcm-2 . Our results revealed the possibility of improving both Voc and Jsc of the Cu2O homojunction by introducing a ZnO buffer layer.
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.
Growth of Electrodeposited n-Cu2O Thin Films with Tunable Band Edge Position
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Kafi, F.S.B.; Jayathilekea, K.M.D.C.; Wijesundera, R.P.; Siripala, W.
Cuprous oxide (Cu2O) is one of the best candidate for low cost photovoltaic applications due to its optoelectronic properties. Cu2O based solar cell devices have already been reported but the efficiency of the devices are very low compare to the theoretical efficiency limit of 20 %. One of the major drawbacks of the PV devices made with Cu2O is the unfavorable band edge positions of the semicondcutors in contact. Indeed, the possibility of relative band edge shifts of Cu2O with suitable interfacing materials will pave the way for interface engineering to improve the efficiency of Cu2O based devices. In this study we have investigated this possibility of using electrodeposited n-type cuprous oxide thin films deposited using an acetate bath containing 0.1M sodium acetate and 0.01M cupric acetate at various pH values. In order to fabricate Au/n-Cu2O Schottky junction, thin Au layers having the area of 2X2 mm2 were sputtered on these Cu2O films and then these samples were employed with capacitance-voltage measurements to study the flat band potential variations with the pH of the Cu2O film deposition baths. It was observed that pH value of the Cu2O film deposition bath is very sensitive to the flat band potential and observed the flat band potential shift of about 450 mV in the negative direction, as the pH of the deposition bath was changed from 6.2 to 5.5. This result gives a direct evidence that the surface of n-Cu2O film can be modified with the deposition bath pH. The observed shift in the flat band potential is very useful to match the band edge positions of the p-type semicondcutors in contact to fabricate high efficient Cu2O base PV device. National Research council is gratefully acknowledged for the financial assistance through the research grant NRC 15-41.
Improvement of p-Cu2O/Au interface by controlling the pH of the electrodeposition bath of Cu2O
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Kafi, F.S.B.; Jayathilekea, K.M.D.C.; Wijesundera, R.P.; Siripala, W.
Metal-Semiconductor junction studies play a very important role in discovering new junction properties leading to improved electronic devices. Indeed, Schottky junction is among the fundamental structures used in modern optoelectronics and microwave devices. In this regard, low cost and eco-friendly metal-semiconductor devices with inexpensive materials and fabrication techniques are extremely important. Among other materials, p-Cu2O thin films grown by electrodeposition method have attracted as potential candidates for developing Cu2O based low cost Schottky junction devices. In this study, dependence of the p-Cu2O/Au junction properties on the pH of the Cu2O film deposition bath has been investigated for the development of low cost devices. p-Cu2O thin films were potentiostatically electrodeposited in a three electrode electrochemical cell containing 3M lactic acid, 0.4M CuSO4 and NaOH at different pH values. p-Cu2O/Au Schottky junctions were fabricated by sputtering Au on masked Cu2O samples. Dark Capacitance – Voltage measurements (Mott- Schottky plots) of the fabricated devices revealed that a positive shift of 620 mV of the flat band potential against Au for the change in pH of the film deposition bath from 7.0 to 13.0. This positive shift is significant when compared to the positive shift of 350 mV at the p-Cu2O/electrolyte interface observed earlier. The interaction of surface atoms with the electrolyte species at the Cu2O/electrolyte interface and the presence of bare surface atoms at the Cu2O/Au interface might have led to this improvement. The positive shift of the flat band potential manifests that the positive shift in the valence band edge of p-Cu2O relative to the Fermi level of Au increases the barrier height at the p-Cu2O/Au interface. Thus, the study reveals that the barrier height at the p-Cu2O/Au interface can be controlled with the pH of the film deposition both. As observed, dark Current-Voltage measurements on p-Cu2O/Au devices resulted nearly ohmic behavior for low pH values and non ohmic diode behavior for high pH values. This suggests that for high pH values of the film deposition bath of p-Cu2O improved Schottky junctions can be in fabricated with Au, suitable for various device applications such as rectifying circuits, photovoltaics, etc.
Observation of interface modification of electrodeposited p-Cu2O thin films in an aqueous electrolyte
(Faculty of Graduate Studies, University of Kelaniya, 2015) Kafi, F.S.B.; Jayathilekea, K.M.D.C.; Wijesundera, R.P.; Siripala, W.
Interface engineering via modification of semiconductor surfaces of junction devices is a powerful technique to improve the performance of devices. In addition, semiconductor material Cu2O has recently gained a considerable attention as a low cost semiconductor material suitable for developing thin film solar cells, water splitting in photoelectrochemical cells and gas sensors. Indeed, the possibility of relative band edge shifts of Cu2O with suitable interfacing materials will pave the way for interface engineering to improve the efficiency of those devices. In this study we have investigated this possibility of using electrodeposited p-type cuprous oxide thin films deposited using a lactate bath containing 3 M sodium lactate and 0.4 M CuSO4 at various pH values. These Cu2O films were used in a photolectrochemical cell to form semiconductor/electrolyte junctions in a 0.1 M sodium acetate aqueous solution and then to measure the flat band potential variations with the pH of the Cu2O film deposition baths. It was observed that pH value of the Cu2O film deposition bath is very sensitive to the flat band potential. This result gives a direct evidence that the surface of Cu2O film is modified at the Cu2O/electrolyte interface producing a relative band edge shift yielding the observed flat band shifts. We observed a general trend of flat band potential shift of about 350 mV in the positive direction, as the pH of the deposition bath was changed from 7 to 12.5. The observed shift in the flat band potential in the positive direction is very useful for the water splitting reaction because the valence band edge of Cu2O is shifted positively relative to the oxygen redox potential. Our observation of highest photoresponse for Cu2O thin films prepared at pH 13.5 is a direct evidence for the positive shift of the band edges. The observation of the interface modification of Cu2O in aqueous electrolyte may be further extended to other suitable interfaces for developing Cu2O based junction devices.