Browsing by Author "Fernando, C. A. N."

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    Cu2O Quantum Dots (QDs) Sensitized Cu/p-CuI Photo-electrode for H2 Generation through Efficient Water Splitting
    (Uva Wellassa University of Sri Lanka, 2015) Rajapaksha, R. D. A. A.; Fernando, C. A. N.; De Silva, S. N. T.
    Water splitting by sunlight to generate hydrogen and oxygen is a fascinating way of energy production. Metal oxides such as Cu2O, TiO2, ZnO and WO3 with various morphologies have been investigated for water splitting (Fujishima & Honda, 1972). However, most of these metal oxides have large band gaps, which limit the light absorption in the visible region and hence the overall efficiency of the process. To achieve a better photoelectrochemical response with these materials, an extensive research has been done on adding nanostructures (Feng et al., 2008; Wu & Yu, 2004). One possibility is the use of semiconductor nanocrystals (3D nanostructure), known as quantum dots (QDs), as an alternative to this problem (Adachi et al., 2004). In this research study, H2 generation at QDs is presented for the first time efficiently. Energy level positions were used to confirm the QD sensitization process associated at Cu/p-CuI/QD electrolyte interface. Methodology M) solution and boiled until the formation of Cu2O QDs on p-CuI nano-particles at Cu/p-CuI. Variation in boiling time produce various sizes of Cu2O QD on Cu/p-CuI electrode and colour variation according to the boiling time is shown in Fig.1 (b-f). Table 1 shows the variation of the extent of Cu2O QD produced on the Cu/CuI photoelectrode by weight with boiling time in CuSO4 solution. The mechanism of the formation of QDs on the p-CuI particles may be presented from the following reaction.
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    CuO free p-Cu2O nano-surfaces prepared by oxidizing copper sheets with a slow heating rate exhibiting the highest photocurrent and the H2 evaluation rate
    (Uva Wellassa University of Sri Lanka, 2015) Liyanaarachchi, U. S.; Fernando, C. A. N.; De Silva, S. N. T.
    Among the various metal oxide materials for solar energy applications, p-type cuprous oxide (p- Cu2O) is a promising non-toxic and low cost semiconductor with attracted attention for many decades (Mittiga et al., 2006). It was reported that p-Cu2O can be prepared by various fabrication processes such as thermal oxidation, electrochemical oxidation, chemical bath deposition and chemical vapor deposition. Low energy conversion efficiency of p-Cu2O based solar energy conversion devices is due to the prevention of the photo-generated charge carrier separation in the micron–sized Cu2O grains on the surface enhancing the recombination process. If the grains radius is reduced from micron to nano-size, the opportunities for recombination can be dramatically reduced enhancing the light absorption properties of the films. Therefore, the preparation of nano- crystalline Cu2O thin films is a key factor to improve the performance of solar application devices without destroying the crystalline properties of the Cu2O films. Hence, the present work is aim to fabricate CuO free nano-crystalline p-Cu2O by thermal oxidation of copper sheets under maintaining slow heating rate for the first time. Structural and photoelectrochemical properties are also aimed to study. Methodology The outer layers of commercially available (99.99% purity) copper sheets 2cm×4cm were removed by sand papers and polished with Brasso Metal Polisher until obtaining a mirror like surface. Thereafter, polished copper sheets were washed with a surface detergent and distilled water several times. Well cleaned copper sheets were inserted into a Quartz Tube in a Cabolite- 301 Tube Furnace opening both ends by filling normal air during the oxidation process. Initially a heating rate 10 C/min was provided inside the furnace with copper sheets starting from the room temperature. After reaching 300 C, 400 C, 450 C and 700 C the temperature kept constant for 30min and then cooled down to room temperature. Experimentally that it was found that the 10 C/min heating rate was the most suitable to fabricate mechanically stable p-Cu2O on copper C temperature profiles did not produce mechanically stable Cu2O films on copper sheets. Furnace temperature below 300 C was not sufficient to oxidize copper sheets to form quality Cu2O surfaces.Fig.2 shows the appearance of the Cu2O films prepared. Four different surface colors exhibited at each temperature profile expecting four different surface morphologies. Result and Discussion Fig.01 shows the diffuse reflectance spectra for the samples prepared from 300ºC, 400ºC, 450ºC and 700ºC temperature profiles. For the samples prepared from 300ºC, 400ºC and 450ºC temperature profiles show absorption edges 630nm, 620 nm and 600nm, to the band gaps 1.98eV, 2.0eV and 2.1 eV due to band to band transitions of Cu2O. Band gap 1.4eV for an absorption edge ≈850nm can be observed for CuO crystals prepared from 700ºC temperature profile. It should be mentioned that the absorption edges for Cu2O corresponding to the 300ºC, 400 ºC and 450ºC temperature profiles cannot be observed clearly for the samples prepared at 700ºC temperature profile as shown. So that, it can be concluded the most light is absorbed by CuO regions than the Cu2O regions for the samples prepared from 700ºC temperature profile.
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    Quantum Efficiency (Φ) Enhancement of p-CuI Sensitized LB Films of Methylviolet-C18 by Minimizing Dye Aggregates
    (Uva Wellassa University of Sri Lanka, 2015) Karunarathna, P. G. D. C. K.; Fernando, C. A. N.; De Silva, S. N. T.
    It is well known that the spectral response of wide band gap semiconductor materials can be extended to the visible region by deposition of suitable dyes on the surface (Senadeera et al., 2005; Fernando et al., 2013). In addition to the adustability of the spectral response, dye sensitized solar cells have several advantages (Kubo et al., 2002). The dye sensitized photocurrent is rather insensitive to the impurites and the defects of the semiconductor. When dyes with intense absorption bands are deposited, the light absorption at the sensitized surface becomes much higher than a bare semiconductor surface. Although the absorption properties of the dye increases with the concentration of the absorbed dye on the semiconductor surface, a dye sensitized photocurrent enhacement cannot be observed with the increase of the number of dye molecules on the semicondutor because of the energy dissipative proceses of the excited states of the dye and the recombination of photogenerated charge carriers (Fernando et al., 1994). Methodology Commercially available well cleaned copper sheets (1cmx3cm) were used to deposit p-CuI nano thin films from the following method. A solution of CuI was prepared by dissolving 5mg of CuI in 10ml of moisture free acetonitrile. CuI colloidal solution was lightly spread on the well cleaned copper surface until forming a thickness ≈ 5.0 µm to prepare Cu/p-CuI photoelectrodes. Cu/p- CuI photoelectrodes were used to deposit LB films. Experimental set up used for LB deposition is shown in the Fig.1 (Fernando et al., 2013). 2M KI and 1x10 M NaH2PO4- Na2HPO4 pH=6 buffer solution was used as the electrolyte. AFM pictures of the samples were obtained using a Park’s AFMXE-70 Instrument. Photocurrent quantum efficiency (Ф%) was calculated using the following equation, Ф% = [number of electrons created / number of photons incident]x100%