Received Date: October 07, 2015; Accepted Date: October 27, 2015; Published Date: November 10, 2015
Citation:Mohammed IK, Kasim Uthman ISAH, Yabagi JA, Taufiq S (2015) The Effect on Extracting Solvents using Natural Dye Extracts from Hyphaene thebaica for Dye-sensitized Solar Cells. J Material Sci Eng 4:208. doi:10.4172/2169-0022.1000208
Copyright: ©2015 Mohammed IK, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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This study covers the fabrication and characterization of dye sensitized solar cell using Hyphaene thebaica as the natural dye sensitizer for DSSCs. Ethanol and water in separate container was used as the extracting solvent for the natural dyes. Titanium dioxide (TiO2) was deposited on fluorine doped tin oxide (FTO) conductive glass forming a TiO2 thin film, underwent sintering at 400ºC for 40 minutes. The photo electrochemical performance of the dye sensitized solar cell (DSSC) based on the doum palm pericarp shows open circuit voltage (Voc) of 0.37 V and 0.50 V, and short circuit current density (Jsc) of 0.005 mA/cm2 and 0.010 mA/cm2 for ethanol and water extracts respectively. This study further inspected the fill factor as 0.63 and 0.66 for the ethanol and water extract respectively. The conversion efficiency for the ethanol extract was 0.012% and water extract is up to 0.033% under light intensity of 1000 m/Wm2 (AM 1.5).
Dye-sensitized solar cell; Hyphaene thebaica; Doum pericarp; Titanium dioxide
Energy technology is one of the most important technologies in the 21st century that dominated people’s life and people’s consumption. Moreover, environmental pollution has increasingly become a worldwide concern in the past few decades. Thus, how to enhance the efficiency of natural energy use and to recycle regenerated energy has become an important research field for developed countries .
Dye-sensitized solar cells (DSSCs) have been widely investigated as one of the next-generation solar cell because of their simple structure and low manufacturing cost . Generally, DSSC comprises of a nanocrystalline titanium dioxide (TiO2) electrode modified with a dye fabricated on a transparent conducting oxide (TCO), a platinum (Pt) counter electrode, and an electrolyte solution with a dissolved iodine/triiodide ion redox couple between the electrodes . Although certified conversion efficiency using black dye has been reported to be 10.4% by the Swiss Federal Institute of Technology in Lausanne (EPFL) . It is well known that the conversion efficiency (η) of solar cells can be represented as follows Kimpa .
where FF, ISC,VOC, and Pin are fill factor, short circuit current, open circuit voltage, and incident power, respectively.
Organic dye have higher absorption efficient used for DSSCs with efficiencies of up to 9% have been reported . Organic dyes with high absorption coefficient could translate into thinner nanostructure metal oxide film. This advantageous of transporting charge both in the metal oxide and in the permeating phase, allowing for the use of higher viscosity materials such as ionic liquids, solid electrolytes or holes conductors.
In nature, some fruits, flowers, leaves and so on show various colors and contain several pigments that can be easily extracted and then employed in DSSCs. The leaves of most green plants are rich in chlorophyll and the application of this kind of natural dye has been frequently investigated in many related studies. Anthocyanins are natural compounds that give color to fruits and plants and are also largely responsible for the purple–red color of autumn leaves and for the red color of flower buds .
Kimpa used the extract of flame tree flower and pawpaw leaf as photosensitizer and the open-circuit voltage (VOC) of fabricated DSSCs is 0.51 V and 0.50 V . Zhu investigated the extract of frozen blackberries to serve as photosensitizer and the open-circuit voltage (VOC) of fabricated DSSCs is 0.33 V . Polo extracted the blue violet anthocyanin of Jaboticaba and Calafate respectively to serve as photosensitizer and the (VOC) of prepared DSSCs is 0.59 V and 0.4 V respectively . Furukawa investigated the extract of red-cabbage, curcumin and red-perilla to serve as natural dye sensitizers for DSSC and the (VOC) is 0.52 V, 0.53 V and 0.49 V respectively. Patrocinio adopted the extract of blueberries and Jaboticaba’s skin to serve as photosensitizer and the (VOC) of prepared DSSCs is 0.59 V and 0.45 V respectively . In this paper, extracts of doum pericap was used as the natural dyes as dye-sensitizers for the preparation of DSSCs. Doum palm fruit (Hyphaene thebaia) is a desert palm tree with edible oval fruit, originally native to the Nile valley. It also grows very well in the northern part of Nigeria. It is a member of the palm family, Arecaceae. The trunk of this small palm commonly branches into two like Y and often each branch divides again in a Y form, giving the tree a very distinctive appearance; it is dichotomous and arborescent in nature. It is listed as one of the useful plants of the world. It is represented by the genus Hyphaene, the fruit of interest in the current study. Its fibre and leaflets are used by people along the Nile to weave baskets. Doum palm fruit is also a source of potent antioxidants. The fruit has a brown outer fibrous flesh which is normally chewed and spewed out. Doum palm kernel is edible when it is unripe but hard when it is ripe. The fruit is depicted in Figure 1.
Doum fruit was peeled and the pericarp was used as the natural plant. The doum pericarp was crushed with a porcelain mortar and pestle, the crushed sample were kept on two different conical flask. The samples were mixed separately with 50 cm3 of ethanol (99% absolute) at room temperature and 50 cm3 of distilled water in a dark room. The solution was filtered separately using filter paper to acquire a pure and natural dye solution. The TiO2 film was prepared by blending 0.2 g of commercial TiO2 powder (Degussa, P25), 0.4 cm3 of nitric acid (0.1 M), 0.08 g of polyethylene glycol (MW 10000) and one drop of a Triton x-100 (a non-ionic surfactant). The mixture was well mixed using an ultrasonic bath for 1 h and the resulting paste was spread over an FTO conductive glass plate (SOLARONIX) having 15 Ω/cm2. TiO2 pastes were deposited on the FTO conductive glass by rigid squeegee and screen printing procedure (polyester mesh of 90) in order to obtain a TiO2 film with a thickness of 9 μm. The active area of DSSC was 1.04 cm2 (1.3 cm × 0.8 cm). The TiO2 thin film was sintered at 450°C for 45 minutes to increase compact- ness of the thin film. The TiO2 film was consolidated through heat treatment, increasing the internal voids of film organization and thus enhancing its absorption performance. Then the sintered TiO2 thin film was immersed for 24 h in the natural dyes prepared, allowing the natural dye molecules to be adsorbed on the surface of TiO2 nanoparticles. Anhydrous alcohol was used to remove any natural dye that had not been adsorbed on the surface of TiO2 nanoparticles. DSSCs were assembled following the procedure described in the literature , the catalyst-coated counter electrode was placed on the top so that the conductive side of the counter electrode faces the TiO2 film. The iodide electrolyte solution (0.5M potassium iodide mixed with 0.05M iodine in water-free ethylene glycol) was placed at the edges of the plates. The liquid was drawn into the space between the electrodes by capillary action. Two binder clips were used to hold the electrodes together. In the performance test of the prepared DSSC, xenon (Xe) light of 1000 W was selected to simulate sunlight (AM 1.5), and an I-V curve analyzer (Model 4200 SC) was employed to measure the photoelectric conversion efficiency of the prepared DSSC. The measured results were plotted on I-V curve.
Figure 2 shows the absorption spectra of doum pericarp dye extracts and doum pericarp dye extracts adsorped on TiO2 surface using ethanol and distilled water as extracting solvent. Absorption spectra provide necessary information on the absorption transition between the dye ground state and excited states and the solar energy range absorbed by the dye. The absorption range of doum pericarp dye extracts adsorbed on TiO2 was found within the range of 300 – 450 nm. Doum water extract has two absorption peaks at 350 nm and 400 nm, while the absorption peak of the doum ethanol extract adsorped on TiO2 was only at one absorption peak of 353 nm. It can be seen that after TiO2 nanoparticles was added to doum pericarp extract, its absorption intensity decreases from 440 nm to 350 nm. This property reduces the charge transfer ability of the fabricated DSSCs under normal sunlight thereby reducing the efficiency. The dye pigments belongs to the existence of chromophores and it represents the chemical group that is responsible for the colour of the molecule, that is its ability to absorbed photon. Conjugation of chromophores makes them absorb light of different wavelength and energy. Peak wavelength tend to be shifted towards long wavelength as the size of conjugated system or chromophores increases. The double or two absorption peaks of the doum pericarp dye extracts with distilled water as extracting solvent could be due to the presence of complex chromophores conjugated with other group of chromophores. Figure 3 compares the absorption spectrum of doum pericarp ethanol extract and doum pericarp distilled water extract.
The dye sensitization effect was demonstrated with a DSSC using natural dye from doum pericarp and characterized by current – voltage measurements in Figure 4. Energy conversion efficiency of 0.012% at about 0.1 mW/cm2 solar illumination was obtained from the dye extracts using ethanol as the extracting solvent while 0.033% efficiency was obtained for the dye extract using water as the extracting solvent. Table 1 shows the data acquired from measuring the photoelectric conversion efficiency of the DSSCs. From the result obtained, It was observed that using ethanol as our extracting solvent has better absorption capability than water. In this research work the efficiencies of the cells are both very low.
The absorption range of the dye and the dye adsorbed on TiO2 using ethanol and water as the extracting solvent are within the wavelength of 300 nm, 440 nm. The absorption range for pure dye is between 300 nm – 600 nm as shown in Figure 3. The power conversion efficiency η of the DSSC using doum pericap ethanol extract is 0.012% while that of distilled water as the extracting solvent is up to 0.033%. DSSC efficiency from doum pericarp extract has a very low efficiencies compared to that obtained by Zhu , Kimpa , Polo  and Furukawa . The poor performance of the cell could be linked with various factors, one of which could be the dye used and the ability of the electron transportation to the conduction surface of the TiO2.
The authors would like to thank the entire staff of the Physics Advanced Lab, Sheda Science and Technology Complex (SHESTCO) Abuja for allowing us to used their lab and Federal University of Technology Minna University Board of Research (UBR) for their sponsorship.
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