Development of Dye-Sensitized Solar Cell (DSSC) Using Patterned Indium Tin Oxide (ITO) Glass

Fabrication and testing of DSSC

M. Mazalan*, M. Mohd Noh, Y.Wahab, M. N. Norizan, I. S. Mohamad Advanced Multidisciplinary MEMS-Based Integrated Electronic NCER Centre of Excellence (AMBIENCE)

School of Microelectronic Engineering Universiti Malaysia Perlis

Kuala Perlis, Malaysia *mazleemazalan@unimap.edu.my

Abstract—Dye-sensitized solar cell (DSSC) is the third generation of solar cell which comprises of semiconductor electrode, counter electrode and electrolyte. It utilizes the advantage of the wide band gap semiconductor that sensitized to the light. This paper presents the fabrication of DSSC using natural dyes that extracted from mangosteen pericarp and maqui berry. Before depositing the semiconductor electrode, Titanium Dioxide (TiO2), a pattern of lines on conductive side of Indium Thin Oxide (ITO) glass is developed using Krypton Fluoride (KrF) excimer laser RapidX 250 at AMBIENCE lab. For the analysis, the absorption of the dyes is compared by using UV-Vis spectrophotometer. While, the performance of the patterned DSSC in terms of fill factor, efficiency, current density is investigated by using digital multimeter. As the result, this paper proves that the efficiency of the patterned DSSC is improved for both of the dyes.

Index Terms—Solar Cell, DSSC, natural dyes, excimer laser, KrF.

INTRODUCTION Solar energy can be harvested either by obtaining directly from sunlight or indirect method. Various technologies have been developed to harvest solar energy for instance, solar cells is an effective method and has a high demand in the market. The solar cells are classified into three generations based on the techniques and materials used. First generation solar cells are larger and it is silicon-based photovoltaic cells. The weakness of solar cells limited is availability of silicon, requiring expensive manufacturing technology and higher energy photons are wasted as heat. The second generation of solar cells is called thin-film solar cells, which are cheaper than the previous generation cells but have lower efficiency. The dye sensitized solar cells are the third generation of solar cells which has been developed by O’Regan and Gratzel in 1991 [1]. Even though it still in the research phase, the results are promising and encouraging. In general, there are two types of the third-generation solar cells which are nanocrystalline solar cells and dye sensitizes solar cells. Both of them did not have a PN junction as in traditional solar cells. These solar

cells provide technical and economic concepts that are reliable alternatives to the present day PN junction solar cells.

Like other solar cells, the DSSCs are used for converting light energy into useable electricity [2]. The performance of the cells are depends on the molecule of the dye and semiconductor electrode as sensitizer. The more sensitive type of dye to the light, more photon energy can be trapped thus produce the higher output voltage. There are 3 main processes that occur in DSSC. At first, the dye which has absorbed on a layer of TiO2 will interact with a sunlight that promotes an electron from a lower level orbital to an excited one. When photons from source of light do penetrate the solar cell, photo excitation occurs because the solar cell itself excited with the dye of electrons. Then, the excited electron is injected by the dye into the semiconductor (TiO2) and, the chemical diffusion of electrons from the TiO2 layer into the ITO conductive layer. The circuit should be completed by returning back the electrons to the cell and makes the dye back to the “normal” state by using an electrolyte solution. The electrolyte solution is a medium that will helps to carry the electrons through the cell. The cell is called a “sandwich” because two conducting glasses are overlapped as shown in Fig. 1. The anode electrode is coated with the layer of TiO2 sensitized with the dye, and the second ITO glass is coated with carbon in order to enhance the interaction with the electrolytic solution.

Fig. 1. Two conducting ITO is overlapped

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METHODOLOGY The fabrication steps of the patterned DSSC are shown in

Fig. 2. It started with cutting the glass into 3 cm by 3 cm square using diamond tip. The cutting line was firstly scribed onto the glass based on the desired dimension and it followed by gently bending the glass to break it into two parts. In this project, the glass works as anode electrode which is made of a transparent conducting material, which is deposited on the inner side of the support substrate. For this purpose, a thin film of ITO coated glass is the best option due to its high electrical properties and transparency.

After the cutting process, the resistivity for both side of the glass is measured in order to determine the conduction side. Then, the ITO glass is patterned using RapidX 250 which is available in AMBIENCE Lab [3] as shown in Fig. 3. The main purpose of developing the patterns on the ITO glass is to ensure more molecules of dye can be absorbed on the surface of the glass thus the efficiency of the DSSC can be improved.

For the semiconductor electrode, the TiO2 is prepared by grind about 1 gram of nanocrystalline TiO2 by Sigma Aldrich with 1.5 ml of very dilute acetic acid solution, 1 ml of de-ionized water and one drop of dish wash. Then, the solution is grinded until a slightly soupy colloidal suspension is obtained as smooth as latex paint consistency. This recipe is enough to paste onto four pieces of ITO glass. Next, some TiO2 paste is placed onto the ITO glass and spread it using a glass rod.

Carbonyl and hydroxyl groups present in the anthocyanin molecule can be bound to the surface of a porous TiO2 film. This makes electron transfer from the anthocyanin molecule to the conduction band of TiO2 [4]. In this project, the anthocyanin of mangosteen and maqui berry are extracted at room temperature. The natural dye is blended for 10 minutes until it shows homogeneous in colour. After that, the ITO glass coated by TiO2 is immersed into the anthocyanins. For the counter-electrode layer, it is simply done by depositing the carbon produced through combustion from a candle onto the surface of the second ITO glass [5]. The method is just passing the ITO glass, conducting side down, through a candle flame in a second. The photovoltaic efficiency of DSSC produced using carbon as the counter electrode shows the good results compared to other type of materials. This is due to the small particles of carbon produced during combustion that studies have found to be as small as 10 nanometers [6].

The full assembly of the DSSC is completed by combining the ITO glass coated by TiO2 and natural dye with the ITO glass coated by carbon. The binder clips are used to hold the electrodes together. The electrolyte liquid is inserted between the gaps of the electrodes by capillary action.

Fig. 2. Fabrication steps of patterned DSSC

Fig. 3. Excimer Laser RapidX 250 in AMBIENCE lab

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RESULT AND DISCUSSION

UV-VIS Spectrophotometer The absorption spectrum and the transmission of extracted

dye of mangosteen pericarp and maqui berry were obtained using UV-Vis. The wavelength range of mangosteen pericarp and maqui berry spectrum lays is between 400-700 nm. The absorption of mangosteen and maqui berry dye extracted is shown in Fig. 4. It shows that both of the dye extracts have the same level of absorbance however the mangosteen pericap dye has higher of maximum wavelength than maqui berry.

(a)

(b)

Fig. 4.The dye absorption of (a) mangosteen pericarp and (b) maqui berry.

Scanning Electron Microscopy The Scanning Electron Microscopy (SEM) is used to

characterize the pattern on the ITO glass substrates. Fig. 5 shows the result of the pattern on the ITO glass with the setup of the RapidX 250 at 11.2 mJ laser energy, 10 pulse/s of laser speed and 50 numbers of pulse.

Fig. 5. Pattern on ITO glass

High Power Microscopy For the observation on the width and depth etched on ITO

glass by the RapidX 250, the high power microscope is used. Fig. 5 shows the width, depth and gap profile of the pattern on the ITO glass.

(a)

(b)

Fig. 6. The (a) width and depth (b) gas profile of the pattern on the ITO

glass

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I-V Characterization For the IV characterization, the DSSC is tested under direct

sunlight. The current-voltage produced is measured using 500 ohm potentiometer as a variable load, current meter (I) and voltmeter (V). The measurement using potentiometer is started from 10 ohm until 100 ohm. The IV characterization is compared between difference dyes and DSSC with laser patterning on ITO glass as depicted in Fig. 7 and Fig. 8 respectively.

(a)

(b)

Fig. 7. I-V characteristic of DSSC using Mangosteen percicarp (a) without pattern (b) with pattern

(a)

(b)

Fig. 8. I-V characteristic of DSSC using Maqui berry (a) without pattern (b) with pattern

From the observation, the voltage of sample is keep

increasing proportionally to the variable resistance. Nevertheless, the current decreases when the variable resistance is increased. A similar observation was also observed for all samples of DSSCs which are extracted from mangosteen pericarp and maqui berry with laser patterning and maqui berry with laser patterning. The short circuit current (Isc), open circuit voltage (Voc), fill factor (FF) and efficiency (η) are calculated and tabulated as shown in Table 1.

Table 1 Comparison of Pmax, Imax, FF and Efficiency

Extract Source Isc (mA)

Voc (mV)

FF Efficiency, η

Mangosteen Pericarp

0.04E-3 2.5E-3 0.48 0.12

Mangosteen Pericarp (Laser Patterned)

0.43E-3 16.2E-3 0.33 0.575

Maqui Berry 0.07E-3 0.2E-3 0.143 0.005

Maqui Berry (Laser Patterned)

15.4E-3 1.79E-3 0.272 0.188

CONCLUSION As the conclusion, the mangosteen pericarp extract has

higher of maximum wavelength as compared to the maqui berry extract based on the absorption analysis using UV-Vis Spectrophotometer. However, both of the extract dyes shows about the same level of absorbance. The efficiency of the DSSC using mangosteen pericarp with laser patterning shows the increment from 0.12 to 0.575. Meanwhile, the efficiency of the patterned DSSC using maqui berry dye is improved from 0.005 to 0.188.These results prove that laser patterning on ITO glass contribute the significant improvement towards better efficiency of DSSC.

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ACKNOWLEDGMENT This work was supported by FRGS grant No. 9003:0339

from University Malaysia Perlis (UniMAP) and Ministry of High Education (MoHE).

REFERENCES

[1] B. O’regan and M. Gratzel,” A Low-Cost, High Efficiency Solar Cell based in Dye Sensitized Colloidal TiO2 Films”, Natural 353 1991, pp. 737 - 740 [2] K. Wong Charee, V. Meeyo and S. Chavadei,” Dye Sensitized Solar Cell using Natural Dyes Extracted from Rosella and Blue Pea Folowers,” Journal of Solar Energy & Solar Cell 2007, pp. 566 – 571 [3] www.ambience.unimap.edu.my [4] Antonio Luque, Steven Hegedus, "Handbook of Photovoltaic Science and Engineering" John Wiley & Sons Ltd Publishers 1st ed. [5] Michael Grätzel Greg P. Smestad, Journal of Chemical Education 1998, 75, 752. [6] David B. Lenhert Samuel L. Manzello, Ahmet Yozgatligil, Michael T. Donovan, George W. Mulholland, Michael R. Zachariah, Wing Tsang, Proceedings of the Combustion Institute 2007, 31, 675.

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