Increasing Efficiency of Dye-Sensitized Solar Cell ( DSSC ) Originating from Yellow Sweet Potato Extract as Dye Sensitizer : Effect of Acetic Acid , Polyethylene Glycol , and Polyvinyl Alcohol as Ti 02 binders H )

Received: 21st June 2020 Revised: 22nd November 2020 Accepted: 25th November 2020 Online: 30th November 2020 This study aimed to obtain the most efficient Dye-Sensitized Solar Cell (DSSC) using yellow sweet potato extract ( Ipomoea Batatas L.) as a dye sensitizer, with acetic acid, polyethyleneglycol (PEG), and polyvinylalcohol (PVA) as Ti02 binding solution. This research includes the preparation of Ti02 paste with variations: 4 g Ti02 plus 2 M acetic acid (Paste-i), 3.5 g Ti02 plus 15 mL PEG400 (Paste-2), and 0.5 g Ti02 plus 0.75 mL. PVA (Paste-3). Anthocyanin dye from yellow sweet potato was prepared and used to soak the Ti02 photoelectrode for 24 hours. UV-vis and FTIR spectra of dye solution from yellow sweet potato extract showed anthocyanin content at a maximum wavelength of 283 nm and were strengthened by the appearance of hydroxyl groups in the infrared spectra. The highest DSSC efficiency of 0.302% was obtained from PVA as a Ti02 binder, with an electric current of 0.0204 mA and an electric voltage of 338 mv.


Introduction
Energy demand continues to increase along with population growth and development progress in technology, industry, and information. The need for energy, which has been relying on fossil fuels, has resulted in reduced fossil resources, particularly petroleum. Fossil energy sources are non-renewable energy sources because the formation process takes a long time, so alternative energy is vital. Energy conservation that utilizes renewable energy resources can be used as a solution as an alternative energy source, such as wind energy, solar energy, water energy, biomass, and geothermal.
Indonesia, which is located on the equator, has considerable renewable energy potential, especially solar energy. Solar energy is possible to be used as a substitute solution for fossil energy resources. Solar radiation can be directly converted into electrical energy through a conversion device called solar cells. Current solar cell technology has entered the development stage of the is TCO (Transparent Conducting Oxide) glass coated with a wide-slit semiconductor such as Ti02, which is then immersed in dye as a photosensitizer, a charge carrier. Meanwhile, the opposite electrode is TCO coated with carbon, which functions as a catalyst to accelerate the redox reaction with electrolytes [8].
Anthocyanin compounds as dye sensitizers from various types of plants have been carried out, including using anthocyanin compounds from mangosteen fruit, which produce a maximum efficiency value of 2.2 x io3 % [ 9 ]. The use of roselle flower extract resulting in an efficiency of 0.01883 % has also been reported [10].
Monzir et al. [11] used PEG as a Ti02 binder with various natural dyes and obtained the highest efficiency of 0.56 %. Meanwhile, the study, which used acetic acid as a Ti02 binding solution and dragon fruit as a dye sensitizer, obtained an efficiency of 0.0006% [12]. The use of polyvinyl alcohol in the mixture of Ti02 paste with synthetic dye N 719 resulted in an efficiency of 2.05 % [ 13 ].
1. Paste-i. 4 g Ti02 was dissolved in distilled water then stirred until homogeneous. Then to the mixture, 2 M acetic acid was added dropwise until a paste was obtained.
3 . Paste-3 . 0.5 g of PVA was added with 4.5 mL of distilled water. The mixture is then stirred with a magnetic stirrer at a temperature of 8o°C for approximately 30 minutes until the solution thickens and is homogeneous. The solution that has been made was added to 0.5 g of Ti02 powder, with a ratio of 2 spoons of Ti02 spatula mixed with 15 drops or 0.75 mL of PVA solution to form a Ti02 paste.

. Preparation of Yellow Sweet Potato Dye Solution
The yellow sweet potato was extracted by drying in an oven at 105°C for 24 hours and mashed in a blender. The powder was then crushed again in a porcelain cup, filtered using Whatman filter paper to take 50 grams. Yellow sweet potato powder was dissolved in 100 mL distilled water and 21 mL ethanol. The mixture was stirred for 20 minutes, then filtered and stored in a dark bottle.

Electrolyte Solution Preparation
The electrolyte solution used in this study was the redox pair iodine, and iodide ( 17 I 3 " ) gel made [16]. 0.83 grams of Potassium iodide was mixed into 1 mL of distilled water, then added 9 mL of acetonitrile or 10 mL of PEG 400 solution. 0.127 grams of iodine (I 2 ) was added to the solution and then stirred using a magnetic stirrer. The solution was stored in a dark bottle and tightly closed.

. Preparation of reference electrode
The reference electrode was made of carbon-coated FTO glass. Carbon coating on FTO glass was by evenly scratching a 6B pencil on the FTO glass ' s conductive part, then heating it over a candle flame to form a black layer [ 17 ].

Assembly of Dye-Sensitized Solar Cell (DSSC)
An area of 2.5 x 2.5 cm FTO glass was formed where Ti02 was deposited with tape on the conductive part of the glass so that a size of 2 x 2.5 cm was formed as shown in Figure 1. Paste-1 was deposited over the area made on the conductive glass with the help of a stir stick (doctor blading method) to spread the paste. The layers were dried for about 15 minutes and heated in a furnace at a temperature of about 450°C for 30 minutes.

2,5 cm
Based on the above references, innovation is still needed for the optimization of the DSSC fabrication. In this research, we tried to use yellow sweet potato as a dye sensitizer. One of the flavonoid compounds in yellow sweet potato is anthocyanin. Anthocyanins can be used as a dye in DSSC as an electron donor [ 14 ]. The dye layer functions as a sensitizer to absorb photons from sunlight [ 15 ].
Apart from the dye, another factor that influences the efficiency of DSSC is the Ti02 paste used. Ti02 in DSSC is an anode, which will multiply the electrons flowing from the conduction band to the valence band so that the photocatalyst reaction space and dye adsorption will be more. In other words, the absorption spectrum becomes wide. The purpose of this study was to determine the effect of acetic acid, polyethylene glycol, or polyvinyl alcohol as a Ti02 binder in producing the highest efficiency (current and voltage) values in DSSC, using anthocyanin sensitizer from yellow sweet potato extract.

Materials and equipment
The equipment used in this study were the

Ti02 Paste Preparation
Ti02 paste was prepared by mixing Ti02 powder and various binder solutions. The binder solutions used were acetic acid, polyethylene glycol (PEG), and polyvinyl alcohol (PVA).  The Ti02 layer was then immersed in a dye solution of yellow sweet potato extract for 24 hours so that the Ti02 layer turned brownish-yellow. The anthocyanin adsorption occurred on the Ti02 surface. The Ti02 layer soaked in dye was rinsed first with distilled water, with ethanol, then dried with a tissue paper. Polymer gel electrolyte was dropped on the Ti02 surface and covered with a reference electrode to form a sandwich structure [18]. The cell structure was clamped with paper clips on both sides to secure the two electrodes, as shown in Figure 2. The DSSC cells were regenerated using Paste-2 and Paste-3 , starting from the paste deposition step on the FTO glass to assembling the sandwich structure to obtain three DSSC cell structures.  Before being used as a sensitizer, the yellow sweet potato extract was characterized using a UV-Vis Spectrophotometer. This characterization was carried out to determine the absorption of light by anthocyanin pigments from yellow sweet potato. The absorbance spectrum was measured over the wavelength range of 400 -800 nm.

.2.Determination of Functional Groups
A functional group measurement was carried out to determine whether the extracted compound was an anthocyanin. The determination of functional groups was carried out using FTIR Spectrophotometry by looking at the specific peaks showing the types of functional groups possessed by anthocyanin compounds in yellow sweet potatoes. Dye samples from pure yellow sweet potato extract and dye samples from isolated yellow sweet potato extract added with Ti02 crystals were measured for their functional groups.

. 3 .Measurement of Electric Voltage and Current
The performance of Ti02 -DSSC thin layer solar cells was carried out by measuring current and voltage. The DSSC cell measurements were carried out with a multimeter and sunlight as a light source [ 19 ], as shown in nm. There are aromatic compounds as the center of the chromophore group of the phalnoid group compounds, the -OH group substituted for benzene, and the C = 0 group. The absorbance results showed that the yellow sweet potato extract was good enough to be used as a dye source in DSSC. The molecules in yellow sweet potato extract as DSSC sensitizers are expected to have (1) panchromatic properties, namely being able to absorb all visible colors of light at 500 -580 nm [8], (2) to have functional groups that allow it to be bound to the conduction band of wide-slit material (titanium dioxide), ( 3 ) to have an appropriate level of excitation energy and ( 4 ) to have chemical and physical stability, especially heat stability. Yellow sweet potato extract produces high absorption power, which means that the ability of yellow sweet potato dye to absorb photons emitted by sunlight is also large to excite the electrons contained in the Ti02 semiconductor from the conduction band and improve the performance of solar cells.
Spectra measurements were carried out at a wavenumber of 4000 -600 cm 1 . The FTIR spectra results are presented in Figure 5 . The dye ' s FTIR spectra showed absorption at a wavenumber of 3253.44 cm 1 derived from a hydroxyl group, which can form a hydrogen bond. Also, the absorption at the wave number 1045.49 cm appears from the -C-0 bond of the alcohol. This OH group ' s presence indicates the presence of a phenol OH group in anthocyanin compounds or alcohol compounds in the dye solution. The alcohol compound in the solution comes from one of the anthocyanin solvent constituents, which is ethanol. Alcohol can also be formed from the hydrolysis of glucosides found in anthocyanins to become alcohols called aglycones and sugar molecules. The double bond absorption -C = Caromatic is shown by the sharp absorption at the wave number 1636.18 cm -1 . The peak at 2122.79 cm -1 originated from the -C C-group ' s stretching vibration, while the peak at 1248.61 cm -1 came from the stretching vibration of the aromatic ether group. Based on the FTIR spectrum results, it can be concluded that the extracted compound is anthocyanin. Another study using purple sweet potato as dye sensitizer produced almost the same FTIR spectra, which were at a wavenumber of 3348.

. Functional Groups
Furthermore, to determine the functional groups contained in the yellow sweet potato extract was carried out by FTIR analysis. The condition for an electric current in the DSSC circuit is the bonding of the anthocyanin dye molecule with Ti02. Anthocyanin dye molecules that bind to Ti02 in the presence of light cause excitation of electrons to the Ti02 semiconductor conduction band through the glass conducting. These electrons cause an electric current. The bond that occurs in the anthocyanin dye with Ti02 can occur through a chelate bond. This bond can occur between the hydroxyl group of the anthocyanin and the Ti 4 + group on Ti02.
When the light in the form of photons hits the DSSC cells, the energy from these photons is absorbed by the yellow sweet potato dye extract. The difference in the energy level of the absorbed photons depends on the dye used. The absorption of the photon energy causes the electrons in the dye to get excited. The presence of microparticle titanium dioxide semiconductors causes the dye to adhere to during the dyeing process. The more dye adheres, the more photoelectrons are produced. The excited electrons are then injected into the titanium dioxide conduction band so that the titanium dioxide acts as an n-type semiconductor. The injected photoelectrons move along the nanoparticles towards the top conduction band (anode). After reaching the anode, the photoelectrons move through the electrical circuit, and the excess energy is converted into electrical energy by the device in the circuit (load). The number of electrons flowing through the load per second is read as current, and the energy possessed by each electron is the voltage or electric potential.

. Current and Voltage
In the DSSC made with various Ti02 binder solutions including acetic acid, polyethylene glycol, and polyvinyl chloride -, the current and voltage tests were carried out using a digital multimeter (Figure 3 ). The light source used was direct sunlight during bright lighting, which was at 12.00 noon.   [20], where Pmax is the using the equation: maximum power produced by DSSC, Pin is the power from the light source used. The pin comes from the sun in Palembang ' s city with a light intensity of around 457 mW / cm 2 . The maximum power is given by the relationship: P generated is Vmax and the maximum current produced The resulting current and voltage measurements and the calculation of the DSSC efficiency of each Ti02 binder solution are presented in Table 2  The results of measurements with multimeters are presented in Table 1, then a graph of the relationship between current and time (days) is made and is shown in Figure 6. The voltage and current generated by the DSSC, although fluctuating from day 1 to day 2, tended to decrease from day 4 to day 80 in each Ti02 binder solution. The efficiency value obtained in each type of Ti02 binder solution on the DSSC is still below the efficiency value of solar cells with silicon-based materials. This is due to the immense value of the constraints contained in the DSSC itself. The easy evaporation process of liquid electrolytes can also degrade DSSC performance. Iodine, a redox component in a liquid electrolyte solution, has low stability because it is easily oxidized by air. This oxidation process is also accelerated by the heat received by the DSSC from the sun. Another factor that also affects the decline in the stability and performance of DSSC is the lack of strength of yellow sweet potato, which is an organic substance as a dye sensitizer.
The maximum efficiency of converting solar energy into electrical energy is obtained in PVA as a Ti02 binding solution, with a value of 0.302 %. Efficiency is calculated from the maximum voltage value of 338 mV and the maximum current value of 0.0204 mA. The initial analysis of why PVA is the most optimal as a Ti02 binder solution to the efficiency of DSSC is because PVA has a high-density value, which is 1.19 -1.31 g / cm 3 , and a boiling point of 228°C.
The second-largest efficiency value was obtained when using acetic acid as a TiCk binder. Acetic acid has physical properties with a density of 1.049 g / cm and a low pH, producing good results in maintaining Ti02 resistance. PEG, a synthetic polymer widely used in industry, is not efficient enough as a Ti02 binder solution in DSSC. Selection of the type of Ti02 binder solution is one of the methods used in research to increase the stability of Ti02. The more stable the Ti02 binder solution is used, the better the electron flow, which, on the whole, determines the resulting efficiency of the solar cell.

. Conclusions
From the results of this study, the Uv-Vis spectra obtained from the Shimadzu UV-1800 and UV-2600 Shimadzu Spectrophotometers show that yellow sweet potato contains anthocyanins, which can be used as a dye sensitizer in DSSC. Meanwhile, FTIR analysis revealed that Ti02 had formed chelate bonds with anthocyanin compounds. The choice of Ti02 binder solution used was 24 -• -Acetic acid --PEG -»-PVA  Figure 6. Correlation of current ( pA) to time (days) with variations of Ti02 binder solution Figure 7 shows the stress of the DSSC with yellow sweet potato as a dye sensitizer with a variation of the three Ti02 binder solutions experiencing a decreasing trend from day 3 to day 80. PVA produces a higher current and voltage value than acetic acid and PEG as Ti02 binder in DSSC. able to increase the efficiency of DSSC, where Ti02, which was bound with PVA, produced higher efficiency than using acetic acid and PEG. DSSC characteristics can be seen from the resulting current and voltage. The efficiency values of each variation of the titanium dioxide binder solution used were acetic acid of 0.203 %, PEG of 0.095 %, and polyvinyl alcohol of 0.302 %.