Opuntia Stricta Fruit as a Novel Natural Dye Material for Dye Sensitized Solar Cell (DSSC) Applications

Transcription

1 Nano Vision, Vol. 5(7-9), , July-September 2015 (An International Research Journal of Nano Science & Technology), ISSN (Print) ISSN (Online) Opuntia Stricta Fruit as a Novel Natural Dye Material for Dye Sensitized Solar Cell (DSSC) Applications S. Sakthivel and V. Baskaran Thin Film Physics and Nano Science Laboratory, PG and Research Department of Physics, Rajah Serfoji Govt., College (Autonomous), Thanjavur, Tamilnadu, INDIA. sakthivel.sunmugam@yahoo.com; bass.physikz@gmail.com. Presented in Second National Conference on Thin Film Science and Nano Technology (SECOND-NCTFSANT-2015) March 2-3, 2015, Rajah Serfoji Govt. College, Thanjavur, T.N. (India). ABSTRACT Natural dye molecules used as light harvesting material in photovoltaic cells. A solid-state absorber used as a sensitizer in conjunction with the Opuntia Stricta fruit dye. Nanostructured Titanium dioxide (TiO 2 ) photo anode prepared by doctor balding technique on chemically sprayed Indium Tin Oxide (ITO) glass substrates. Natural dyes (Opuntia Stricta fruit) have used for the fabrication of dye-sensitized solar cells (DSSC) with a novel route. The surface morphology was studies using X-ray diffraction (XRD), Scanning electron microscopy (SEM). UV - visible absorption spectroscopy did the optical studies. The solar cell efficiency has calculated and found to be 0.59% to 0.90% with different dye conditions. Keywords: Opuntia Stricta fruit dye, DSSC, Titanium dioxide, Doctor Blading. 1. INTRODUCTION Dye-sensitized solar cells (DSSCs) are the third generation of photovoltaic devices for the conversion of visible light in electric energy 1. These new types of solar cells based on the photosensitization produced by the dyes on wide band-gap mesoporous metal oxide semiconductors; this sensitization produced by the dye absorption of part of the visible light spectrum 2. One aspect of these DSSCs photocells that is particularly attractive is the low cost of the solar energy conversion into electricity; this is possible mainly due to the use of inexpensive materials and the relative ease of the fabrication processes 3. The use of natural pigments as sensitizing dye for the conversion of solar energy in electricity is very interesting because, on one hand they enhance the economical aspect and on the other, produce significant benefits from the environmental point of view 4,5. Natural pigments extracted from fruits and vegetables 6, such as chlorophyll and anthocyanins, have extensively investigated as DSSCs

2 188 S. Sakthivel, et al., Nano Vision, Vol.5 (7-9), (2015) sensitizer 7. Cactaceae considered the most promising family among betalain bearing plants to use as a source of betaxanthins. Opuntia fruits are widely consumed in Central and Southern America, Australia, South Africa, and the Mediterranean area. These plants may be found as spontaneous vegetation and grow in all of the semiarid countries, although cultivated cactus pears also reach the market. The main interest in Opuntia fruits attributed to the betalain pigments due to the strong potential candidate of the photovoltaic industry for colourants obtained from natural sources 8. Cactus pear fruits offer different colours based on betalains, which cover a wide spectrum from yellow to purple. Betalains are water-soluble, nitrogen-containing plant pigments of the order Caryophyllales. They comprise the yellow betaxanthins, and the redpurple beta Cyanins, both of which have betalamic acid in their basic structure, its Chromophores is a 1, 7-diazaheptamethinium system, while they differ mainly in the radicals bonded to the main structure 9,10. Their colour is due to the conjugation of a substituted aromatic nucleus to the diaza system, which shifts the absorption maximum from around 535 nm in betacyanins to near 480 nm in betaxanthins. In cactus pear fruits (Opuntia sp.), these pigments are responsible for the purple, red, orange and yellow colours. Betalains recognized as natural food colourants 11, and in contrast to other natural pigments, their appearance maintained over a wide ph range 12. In the present work, we have synthesized TiO 2 films on ITO and fabricated solar cells using Cactus pear fruits (Opuntia Stricta) dye extract. Here we have used carbon coated ITO as counter electrode instead of the conventional Platinum electrode and Iodine compounds acts as a good electro catalyst for the redox reaction 13. The photovoltaic properties are examined, under A.M 1.5 irradiation as a function of open circuit voltage (Voc), short circuit current (Isc), Fill-Factor (FF) and efficiency (η) aiming to determine the conditions that lead to the production of natural dye DSSCs with different solvents. 2. EXPERIMENTAL METHODS 2.1 Deposition of Indium Doped Tin Oxide Thin Films (ITO) 2 M stannic chloride solution of 100 cc was prepared in doubled distilled water and gm of Indium chloride dissolved in it, to obtain the 20% doping concentration of Indium. A few drops of oxalic acid were added in it for removal of whitish precipitate from the above mixture, 10 cc solution was taken as a precursor solution and 10 cc of propane 2-ol was added in it which gives the 20 cc spraying solution. The final solution sprayed through the specially designed glass nozzle at the spray rate of 5 cc per minute. The substrate temperature maintained at 475 o C. It found that, the conducting glasses have S/cm 2 sheet resistance and about 90% transparency Preparation of Working Electrode TiO 2 working electrode was prepared via doctor blade method using titanium tetraisopropoxide (TTIP, Merck), distilled water, ethyl alcohol (EtOH, Merck) as the starting materials. Titanium tetraisopropoxide was dropped slowly into the solution of water and ethyl

3 S. Sakthivel, et al., Nano Vision, Vol.5 (7-9), (2015) 189 alcohol while magnetic agitating continuously to get white slurry solution 15. The obtained solutions kept under slow-speed constant balding on an ITO glass at room temperature. The films heated up to C for 30 minutes using C/min heating ramp rate. The above procedure for TiO 2 films repeated several times in order to make films with thickness around 1.5 microns Preparation of Natural Dye Sensitizer Fresh Cactus pear fruit cut into 100 ml of ethanol. Solid dregs are filtered and to obtain a pure natural dye solution. Then the residual parts removed by filtration and washed with hexane several times to remove any oil or chlorophyll present in the extract. This directly used as dye solution for sensitizing TiO 2 electrodes. The Cactus pear fruit dye extracted from the ethanol solvent at different temperatures such as room temperature, 50 C, 75 C, and 100 C. To study the effect of ph on the performance of solar cell, the ph of the Cactus pear extract solution changed by adding dilute HCl and dye solution with three different ph values 1.0, 2.0, and 3.0 have been used as sensitizer. To study the effect of extracting solvent on the performance of solar cell, the fruit dye also extracted by using methanol at a temperature of 75 C Assembling the Solar Cell To assemble the natural dye sensitized TiO 2 nanostructure based solar cell, the prepared TiO 2 nanostructure electrode were immersed in the synthesized dye solution at room temperature for 24 h, after that period the film was rinsed in anhydrous ethanol and then dried (Fig.1). A carbon-coated ITO counter electrode then placed over the dye-adsorbed TiO 2 nanostructure electrode. A redox electrolyte was prepared using 0.5 mol KI, 0.05 mol I 2, and 0.5 mol 4-tert-butylpyridine and a drop of electrolyte solution was injected into the into the cell Characterization The structure of the prepared films has studied by X-ray diffraction studies using a Rigaku X-ray diffractometer (XRD) using Cu Kα irradiation. The surface morphology of the films were studied using scanning electron microscopy (SEM;VEGA 3 TE SCAN),The photocurrent-voltage (J-V) characteristics of the devices were measured using white light from a (max.150 W) using a sun 2000 solar simulator (Sponsor: MHRD &IIT-BOMBAY). Light intensity adjusted using a Si solar cell to ~AM-1.5. Incident light intensity and active cell area were 100 mwcm 2 (one sun illumination) and 0.4 cm 2 ( cm) respectively. 3. RESULTS AND DISCUSSION 3.1. Structural and Morphological Analysis The as-deposited films show no diffraction peaks of crystalline TiO 2 phase even up to a deposition temperature of 350 o C, presumably, due to either low deposition temperatures or

4 190 S. Sakthivel, et al., Nano Vision, Vol.5 (7-9), (2015) strong deviation from the stoichiometric O/Ti ratio. When the films annealed for 1 hour under oxygen above 500 o C, the original amorphous films became crystalline pure rutile TiO 2 (the crystallinity improved with increasing deposition temperature). Fig.1. (a) X-ray diffraction pattern of the TiO2 film. Figures 1(a) shows the X-ray diffraction patterns of the film. The diffraction peaks observed at , ,39.196,41.241, , 54.32,56.628,65.515, and are attributed to the (110), (101),(200),(111), (210), (211),(220),(221),(112) and (400) planes respectively, of tetragonal structure, as can be seen in comparison with the JCPDS card no The films are polycrystalline in nature and highly oriented along (110) plane. The average crystallite size for the (110), (101), (220), and (112) XRD peaks was found to be between nm. The calculated lattice parameter a=4.610 nm and c = The average grain size was 12 nm, calculated from the broadening of the (110) line by Scherrer s formula. Fig.1. (b) SEM image of TiO2 thin film (c) Absorbance spectra of Cactus pear fruit dye The SEM investigation revealed that the crystallites are homogeneous and in nanometer size. Figure 1(b) shows the grain sizes are spherical in uniform shape and the distribution closely packed giving rise to little mesoporous and voids. It could observe from the micrographs that the film was highly mesoporous in nature and contained particles of uniform size in aggregated clusters consisting of many nanoparticles. Fig. 1(c) shows the UV

5 S. Sakthivel, et al., Nano Vision, Vol.5 (7-9), (2015) 191 Vis spectra of Cactus pear fruit extracted with two different solvents adsorbed on TiO 2 film. A similar shape of the absorption spectra observed between the betalain and betaxanthins; this result indicates that betalain is the major component of Cactus pear fruit. The absorption spectra that Cactus pear fruit extract adsorbed on TiO 2 is obviously wider and red shift compared with that in ethanol and methanol solutions (Fig.1(c)).When the dyes adsorbed on the TiO 2 film, the average value of the shift is 10 nm, which means that the interaction formed through the C O Ti chemical bond I-V characterization of the Solar Cell Figure.2 shows the photocurrent density-voltage (J-V) characteristics of natural dyes (prepared at room temperature) sensitized TiO 2 nanostructure based solar cells. The conversion efficiency (η) of the Cactus pear fruits extract sensitized TiO 2 nanostructure based solar cell is 0.90% with short circuit current density ma/cm 2, open circuit voltage of V and fill factor of Figure (2, 3): J-V characteristics of Cactus pear fruit dye & extracted at different ph values Table 1: Solar cell parameters of the TiO2 sensitized with Cactus pear fruit dye Natural Dye V oc (V) J sc (ma/cm 2 ) FF % Cell Efficiency η % Cactus pear fruit Table 2: Solar cell parameters of the cells sensitized with Cactus pear fruit dye extracted with different ph Values ph V oc (V) J sc (ma/cm 2 ) FF % Cell Efficiency η %

6 192 S. Sakthivel, et al., Nano Vision, Vol.5 (7-9), (2015) The ph of the dye extract has an important effect on the performance of Cactus pear fruit natural dye sensitized solar cells and it shown in Table 2. The solar cells fabricated using TiO 2 nanostructure sensitized using dye extract with ph values 1, 2 and 3 show efficiency values of 0.59%, 0.90%, 0.74 % respectively(fig.3). The dyes synthesized at ph = 2 shows good interaction with the working electrode, the reason is at ph = 2, the betalamic acid existed as betalain ion, which is stable form of betaxanthins; an increasing ph hydrated this ion to quinonoidal bases. However, the cell deterioration by acid leaching is expected as the ph goes lower (ph = 1), which results in a lower efficiency. Figure (4, 5): J-V characteristics of natural dye extracted at different temperatures & solvents The effect of dye extracting temperature on the solar cell performance was shows in Table 3. Solar cell sensitized using dye extracted at 50 C shows a power conversion efficiency of 0.79%, with Voc of V, Jsc of 2.41 ma/cm 2 and FF of Solar cell sensitized using the dye extracted at 75 C shows power conversion efficiency of 0.72%, with Voc of V, Jsc of 2.37 ma/cm 2 and FF of Solar cell sensitized using dye extracted at 100 C shows a conversion efficiency of 0.61% with Voc of V, Jsc of ma/cm 2 and FF of 0.51(Fig.4). Figure 5.shows the photocurrent density-voltage (J-V) characteristics of natural dye (extracted using different solvent) Sensitized TiO 2 nanostructure based solar cells. As shown in Table 4, the solar cells prepared using natural dye extracted in ethanol shows a higher efficiency than that of Solar cells prepared using natural dye extracted in methanol. Table: 3. Solar cell parameters of the cells sensitized with Cactus pear fruit dye extracted with different temperatures. Temperature o C V oc (V) J sc (ma/cm 2 ) FF % Cell Efficiency η % Room temp C C C

7 S. Sakthivel, et al., Nano Vision, Vol.5 (7-9), (2015) 193 Table: 4. Solar cell parameters of the cells sensitized with Cactus pear fruit dye extracted with different solvents The Figure (5) clearly shows that the dye extracted using methanol absorbs less light compared to that of the dye extracted using ethanol. Finally, DSSCs as promising alternatives to the conventional silicon based solar cells require specific modifications and inspired connections before they can apply to a production line. The electrolyte thickness, the efficient current collection, and effective isolation of the cells to the module are of the main issues to solve before. 4. CONCLUSION The dye-sensitized TiO 2 nanocrystalline based Cactus pear fruit natural dye photovoltaic cell in case of global power conversion efficiency of solar energy to electricity conversion and cost needed to manufacture such cell has proven to be serious competitor to today widely used Conventional solar cell. X-ray diffraction pattern for TiO 2 shows tetragonal structure, as can be seen in comparison with the JCPDS card nos The films are polycrystalline in nature and highly oriented along (110) plane. The average crystallite size for the XRD peaks found to be between nm. The calculated lattice parameter a=4.610 nm and c = The average grain size was 12 nm, calculated from the broadening of the (110) line by Scherrer s formula. The SEM investigation revealed that the crystallites are spherical in shape and the distribution closely packed giving rise to little mesoporous and voids. The efficiency of the solar cells can be enhanced by changing the solvent used in the preparation of the dye, changing the temperature and ph of the extract. Ethanol found to be the suitable solvent for natural dye; the optimum dye extracting at room temperature found to be 0.90 % and the suitable value of ph found to be 2. Further optimization of the cell is possible for achieving higher efficiencies. We suggest that the optimum dye extracting temperature found to be in between RT to 50 C for Cactus pear fruit based DSSCs. ACKNOWLEDGMENT The authors would like to express their thanks to the University Grants Commission (UGC), New Delhi, India for sanctioning the financial assistance [F. No /2012(SR) Dated: July 2012] to carry out the present research work. REFERENCES solvent V oc (V) J sc (ma/cm 2 ) FF % Cell Efficiency η % Ethanol Methanol Grätzel, M. Solar energy conversion by dye-sensitized photovoltaic cells. Inorg. Chem., 44, (2005).

8 194 S. Sakthivel, et al., Nano Vision, Vol.5 (7-9), (2015) 2. Gomez Ortiz, N.M.; Vázquez-Maldonado, I.A.; Perez Espadas, A, A.R.; Mena-Rejón, G.J.; Azamar-Barrios, J.A.; Oskam, G. Dye-sensitized solar cells with natural dyes extracted from achiote seeds. Solar Energy Mater. Solar Cells, 94, (2010). 3. Angel Ramon Hernandez-Martinez et al., New Dye-Sensitized Solar Cells Obtained from Extracted Bracts of Bougainvillea Glabra and Spectabilis Betalain Pigments by Different Purification Processes, Int. J. Mol. Sci., 12, ; doi: /ijms (2011). 4. Pastore, M.; Mosconi, E.; De Angelis, F.; Gratzel, M. A Computational Investigation of Organic Dyes for Dye-Sensitized Solar Cells: Benchmark, Strategies, and Open Issues. J. Phys. Chem. C,114, (2010). 5. Delcamp, J. H.; Yella, A.; Holcombe, T. W.; Nazeeruddin, M.K.; Gratzel, M. The Molecular Engineering of Organic Sensitizers for Solar-Cell Applications. Angew. Chem., Int. Ed., DOI: /anie (2012). 6. Calogero, G.; Di Marco, G.; Cazzanti, S.; Caramori, S.; Argazzi, R.; Di Carlo, A.D.; Bignozzi, C.A. Efficient dye-sensitized solar cells using red turnip and purple wild sicilian prickly pear fruits. Int. J. Mol. Sci., 11, (2010). 7. Piattelli, M. et al, Betacyanins from Bougainvillea. Phytochemistry, 9, (1970). 8. M. Piattelli: Betalains. In: Chemistry and Biochemistry of Plant Pigments, Vol.1, T.W. Goodwin (Ed.), Academic Press, London, UK, pp (1976). 9. D.A. Moreno, C. García-Viguera, J.I. Gil, A. Gil-Izquierdo,Betalains in the era of global agri-food science, technology and nutritional health, Phytochem. Rev. 7, (2008). 10. U. Wissgott, K. Bortlik, Prospects for new natural food colorants, Trends Food Sci. Technol. 7, (1996). 11. J.D. Adam-Burrows, Palette of our palates: A brief history of food coloring and its regulation, Compr. Rev. Food Sci.Food Safety, 8, (2009). 12. J.A. Fernández-López, L. Almela, J.M. Obón, R. Castellar, Determination of antioxidant constituents in cactus pear fruits, Plant Foods Hum. Nutr., 65, (2010). 13. S. Sakthivel, V. Baskaran and S. Mahenthiran, Dye Sensitized Solar Cell Properties and Fabrication Using Lawsonia Inermis, Journal of Chemistry and Chemical Sciences, Vol. 5(2), 85-92, ISSN X (Print), ISSN (Online). February (2015). 14. S. Sakthivel, V. Baskaran, Fabrication and Electrical Properties of Dye Sensitized Solar Cells Using Henna, Beetroot and Amla Dyes, International Journal of Science and Research (IJSR), ISSN (Online): , (ETPTA-2014), August (2014). 15. A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo, H. Pettersson. Dye Sensitized Solar Cells 110, pp , (2010).