Beta-Carotene Dye of Daucus Carota as Sensitizer on Dye-Sensitized Solar Cell Risa Suryana, 1,a Khoiruddin 1 and Agus Supriyanto 1

Transcription

1 Materials Science Forum Online: ISSN: , Vol. 737, pp doi: / Trans Tech Publications, Switzerland Beta-Carotene Dye of Daucus Carota as Sensitizer on Dye-Sensitized Solar Cell Risa Suryana, 1,a Khoiruddin 1 and Agus Supriyanto 1 1 Department of Physics, Faculty of Mathematics and Natural Sciences Universitas Sebelas Maret Jl. Ir. Sutami 36A Kentingan Surakarta Indonesia a rsuryana@uns.ac.id Keywords:beta-carotene, DSSC, FTO, absorbance, photoconductivity Abstract.Beta-carotene dye which is extracted from daucus carota material was used as sensitizer to fabricate dye-sensitized solar cell (DSSC). DSSCs were arranged in a sandwich structure consisting of fluorine-doped tin oxide (FTO) as a transparent conducting oxide (TCO), titanium dioxide (TiO 2 ) layer, beta-carotene dye, iodide/tri-iodide redox electrolyte,and carbon layer as a counter electrode. Beta-carotene dye has an absorbance in wavelength zones from 415 to 508 nm. Meanwhile, it has the largest photoconductivity of and (Ω.m) -1 in dark and bright conditions, respectively. Moreover, the photoelectrochemical performance of the DSSC based on beta-carotene dye showed that the maximum voltage of V and the maximum current of A. However, the photo-to-electric conversion efficiency of this DSSC was very low i.e %. Introduction More than 20 years ago, Grätzel et al. developed a dye-sensitized solar cell (DSSC) [1] as a cheap alternative to conventional p-n junction solar cells. Since then DSSCs have attracted considerable attention due to their environmental friendliness, easy fabrication, and low cost of production. A DSSC is composed of a photoanode, an iodide/tri-iodide redox electrolyte and a carbonized counter electrode. The photoanode is a nanocrystalline porous semiconductor electrode such as TiO 2 grown on transparent conducting glass. DSSC structures are arranged in sandwich system. Picture and explanation of this system is clearly described in reference [2].In DSSCs, the dye as a sensitizer plays a key role to absorb photon from sunlight or bulb light and convert into electrical current. The types of dye such as metal complexes, organic, and natural is usually used as a sensitizer. Ruthenium-metal complexes absorbed on nanocrystalline TiO 2 have reached efficiency of 11-12% [3] while the organic dye has reached efficiency as high as 9.8% [4]. Although such DSSC has achieved a relatively high efficiency, there are some disadvantages when using metal complexes and organic as sensitizer. A limited number of metal complexes causes costly in production, while the organic dye requires complicated synthetic routes. Although the natural dyes often work poorly in DSSCs, it seems promising as an alternative to replace the metal complexes and organic dyes due to their abundant, non-toxicity, and inexpensive. These facts become a hot topic in the research of DSSCs development. The natural dye can be found in leaves, fruits, and flowers and it can be extracted by simple procedures. Several natural dyes have been utilized as sensitizer in DSSCs, such as anthocyanin[5], betalains [6], and chlorophyll [7].It is known that each dye in DSSCs has unique properties that provide extensive opportunities to study on other dyes. Yamazaki et al. reported that two carotenoids (crocetin and crocin) from extracted gardenia fruit can be used as sensitizer in DSSCs[8]. They obtained the photoelectric conversion efficiency of these DSSCs sensitized with crocetin and crocin are 0.56% and 0.16%, respectively. Beta-carotene is one of carotenoids that can be obtained by extracting the carrot [9]. In this paper, beta-carotene which is used as sensitizer in DSSCs is derived from the extraction of local carrot (daucus carota). Absorption of beta-carotene was characterized by UV-Vis spectrophotometer. The photoelectrochemical properties of DSSCs using this extract as sensitizer was investigated. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-12/05/16,14:04:08)

2 16 Nanotechnology Applications in Energy and Environment Experiment Preparation of Beta-Carotene Dye. Beta-carotene dyes were extracted from carrots (daucus carota) with ethanol. Firstly, carrots were washed with water and cut into about cm 3 and dried at room temperature. Carrot pieces were divided into three group namely S1=20 g, S2=30 g, and S3=40 g. Each group was immersed in 50 ml n-hexane at room temperature for 30 min. Then the solution of each group was filtrated out. The resulting filtrates were used as sensitizer. Preparation of Dye-Sensitized Solar Cells. Fluorine-doped tin oxide (FTO) conductive glass sheets were cleaned in ethanol using ultrasonic bath for 20 min and then dried at room temperature. TiO 2 pastes were deposited on the FTO conductive glass by slip casting method in order to obtain a TiO 2 layer with a thickness of 20 µm and an area of 2 cm 2. The TiO 2 layer was heated at 150 C for 10 min. After cooling to room temperature, the TiO 2 electrode was immersed in an n-hexane solution containing a beta-carotene dye for 1 h. The dye-sensitized TiO 2 electrode and carbon counter electrode were assembled to form a solar cell by sandwiching a redox (I - /I 3 - ) electrolyte solution. Measurements.The absorption spectrum of beta-carotene dye in solution was measured by ultra violet visible (UV-Vis) spectrophotometer (Perkin Elmer Lambda 25) in the wavelength between 350 and 800 nm. The TiO 2 crystalline type was measured by X-ray diffractometer (XRD) Bruker D8 Advanced in the angle (2θ) range from 20 to 80. The basic properties of beta-carotene dyes in solution in the electrical charge transport were determined by IV-meter Elkahfi [10].Schematic of a photocurrent measurement using IV-meter was demonstrated in Fig. 1. Two Cu electrodes were immersed in the solution. The distance between electrodes (L=8 mm) and the immersed electrode area were maintained constant. The external voltage was introduced in the range of 0-9 V and an electrical current can be obtained. The electrical resistivity of the solution can be determined from the equationρ1, where 1 is the gradient of I vs.v curve.the current-voltage curves of the DSSCs were obtained by applying an external bias to the cell and measuring the generated photocurrent under overhead projector (OHP) light irradiation with a Keithley digital source meter (Keithley 2602A, USA). The intensity of the incident light was 1245 Wm -2. The OHP light was also irradiated on the dye solution in order to obtain the generated photocurrent using Elkahfi IV-meter. Fig. 1 Schematic of a photocurrent measurement of beta-caroten dye using IV-meter under OHP light irradiation

3 Materials Science Forum Vol Results and Discussion UV-Vis absorption spectra for the n-hexane extracts of carrot in variation of S1, S2, and S3 are shown in Fig. 2. For all curves, the absorption peaks occur at the same wavelength with a maximum absorption peak occurs at 448 nm. These absorption curves are similar as absorption curve of beta-carotene reported by Karnjanawipagul et al.[9]. Therefore, our extracted carrot is valid as beta-carotene. The peak of S3 curve is higher than S1 and S2 indicating that the content of beta-carotene dye of S3 is much more than that of S1orS2. XRD patterns of TiO 2 powder are shown in Fig. 3. The patterns exhibited strong diffraction peaks at 27.5, 36.2, and These peaks are good agreement with the standard spectrum (JCPDS, PDF # ) indicating TiO 2 in the rutile phase S1 B Absorbance (a.u.) 421 S2 C S3 D λ (nm) Fig. 2 UV-Vis absorption spectra for the n-hexane extracts of carrot in variation of S1, S2, and S3 110 Intensity (a.u.) theta (deg.) Fig. 3 X-ray diffraction of rutile TiO 2

4 18 Nanotechnology Applications in Energy and Environment Conductivity in bright Table 1.Conductivity of beta-carotene dyes for S1, S2, and S3 in dark and bright conditions Dye Conductivity in dark 10-4 [Ωm] [Ωm] -1 S S S Measurement results of conductivity using IV-meter in dark and bright conditions for each beta-carotene dye (S1, S2, and S3) is summarized in Table 1. Sequence of conductivity values from large to small i.e. S3, S2, and S1 in both dark and bright conditions. In addition, based on the UV-Vis curves in Fig. 2, the highest beta-carotene content is S3, while the lowest beta-carotene content is S1. Therefore, it is considered that beta-carotene dye acts as charge carriers. In dark condition, the charge carriers move to each electrode due to the influence of an external voltage. Meanwhile, in bright condition, the charge carriers are enhanced due to the light are absorbed by dye for excitation. Typical current-voltage characteristic curves for DSSCs which are prepared using S3 dye as sensitizer in dark and bright conditions are presented in Fig. 4. The performance of a dye as sensitizer in DSSCs can be evaluated from the short circuit current (Isc), the open circuit potential (Voc), the intensity of the incident light (Is = 1245 Wm -2 for OHP), the fill factor (FF), and energy conversion efficiency (η). The FF is determined using the equation FF = (Vm Im)/(Voc Isc) with Vm and Im can be determined by a way as shown in Fig. 4 on the right side [11]. Meanwhile, the η is determined using the equation η(%) = [(Voc Isc FF)/(Is A)] 100% with A is the TiO 2 area attached on the FTO. From Fig. 4 for S3, these equations give the efficiency value of %. In the same manner as shown in Fig. 4, for S2 and S1, the efficiency values are % and %, respectively. Again, the amount of beta-carotene content in DSSCs as sensitizer is directly proportional to the magnitude of efficiency. The S3 has highest efficiency in comparison with S1 and S2 because S3 has the most beta-carotene content than S1 and S2. However, the obtained efficiencies are low in order of one hundredth of other dyes i.e. yellow rose (0.26%), begonia (0.24%), and Perilla (0.50%) [12]. Kalyanasundaram et al reported that the planar TiO 2 electrodes are not effectively participates in the excited state charge injection process which causes low efficiency. Consequently, the growth of TiO 2 layer on the FTO should be modified. 0,001 Sample S3 Current (A) 0,0008 0,0006 0,0004 0, ,6-0,4-0,2 0 0,2 0,4 0,6 0,8 1-0,0002-0,0004 Dark B Bright C Voltage (V) Fig. 4 Current-voltage characteristic curves for DSSCs prepared using S3 dye as sensitizer in dark and bright conditions. Right image is a magnification of curve at left side which is used to determine the values of Voc, Vm, Isc, and Im. Current (A) Im Isc Bright Vm Voc -0,3-0,2-0,1 0 0,1 0,2 0,3 Voltage (V)

5 Materials Science Forum Vol Summary In this work, a study has been carried out on the beta-carotene dye of daucus carota as sensitizer on dye-sensitized solar cell. The conductivity and DSSC efficiency are directly proportional to amount of beta-carotene. Both the conductivity and the efficiency will be improved to increasing the amount of beta-carotene content. It is considered that beta-carotene dye acts as charge carriers. The DSSC efficiencies using beta-carotene as sensitizer are still low compared to other dye. Due to the planar TiO 2 electrodes are not effectively participates in the excited state charge injection process which causes low efficiency. Consequently, the growth of TiO 2 layer on the FTO should be modified. References [1] B. O Regan, M. Grätzel, A low-cost, high efficiency solar cell based on dye-sensitized colloidal TiO 2 films, Nature 353 (1991) [2] K. Kalyanasundaram, M. Gratzel, Application of functionalized transition metal complexes in photonic and optoelectronic devices, Coordination Chemistry Review 77 (1998) [3] Y. Chiba, A. Islam, Y. Watanabe, R. Komiya, N. Koide, LY. Han, Dye-sensitized Solar Cells with Conversion Efficiency Of 11.1%, Jpn. J. Appl. Phys. 45 (2006) L638-L640. [4] G. Zhang, H. Bala, Y. Cheng, D. Shi, X. Lv, Q. Yu, P. Wang, High efficiency and stable dye-sensitized solar cells with an organic chromophore featuring a binary π-conjugated spacer, Chem. Commun. (2009) [5] R. Ahmadian, Estimating the impact of dye concentration on the photoelectrochemical performance of anthocyanin-sensitized solar cells: a power law model, J. Photonic for Energy 1 (2011) [6] M. R. Narayan, Review: dye-sensitized solar cell based on natural photosensitizer, Renewable and Sustainable Energy Review 16 (2012) [7] X. F. Wang, O. Kitao, Natural chlorophyll-related porphyrins and chlorins for dye-sensitized solar cells, Molecules 17 (2012) [8] E. Yamazaki, M. Murayama, N. Nishikawa, N. Hashimoto, M. Shoyama, O. Kurita, Utilization of natural carotenoids as photosensitizer for dye-sensitized solar cells, Solar Energy 81 (2007) [9] P. Karnjanawipagul, W.Nittayanuntawech, P. Rojsanga, L. Suntornsuk, Analysis of b-carotene in carrot by spectrophotometry, Mahidol University Journal of Pharmaceutical Sciences 37 (2010) [10] Khairurrijal, M. Abdullah, M.M. Munir, A. Surachman, A. Suhendi, Low cost and user-friendly electronic components characterization system for undergraduate students, WSEAS TRANS. on Advances in Engineering Education 3 (2006) [11] S. M. Sze, K. K. Ng, Physics of Semiconductor Devices, third ed., John Wiley and Sons Inc., New Jersey, [12] H. Zhou, L. Wu, Y. Gao, T. Ma, Dye-sensitized solar cells using 20 natural dyes as sensitizer, J. Photochem. Photobiology A: Chem. 219 (2011)

6 Nanotechnology Applications in Energy and Environment / Beta-Carotene Dye of Daucus carota as Sensitizer on Dye-Sensitized Solar Cell /