Performance of complex compound Zn-TPP (5,10,15,20-tetrafenylporphyrin) as a dye sensitizer in increasing the current and voltage of dye sensitized solar cells

Solar cell technology has been widely used, one of them is Dye Sensitized Solar Cell (DSSC), which is a semiconductor device that can convert sunlight into electrical energy. The objective of this research is to learn the character of metal complexes from derivatives porphyrin Zn-TPP (5,10,15,20-tetraphenylporphyrin) and apply it as a dye sensitizer in DSSC. Zn(II)-TPP complex compound showed a maximum wavelength at 423 nm on the Soret band. Zn-N bond formed between metal and ligand is indicated at 324,04 cm-1. Zn (II)-TPP complex compound is ionic and best used in DSSC applications. The performance (efficiency) of Zn (II)-TPP complex as dye sensitizer in DSSC shows a maximum current of 8 mA/cm2 with a maximum voltage of 0.60 V and an efficiency value of 9.43%.


Introduction
Globally, the primary energy sources that are utilized are fossil fuels, including coal, natural gas, and oil [1].Since there is currently a growing market for various kinds of fossil fuels, numerous researchers are working to identify clean, dependable fossil fuel substitutes.The use of fossil fuels should be limited since they can have a negative impact on the environment and public health [2].As a result, we require renewable energy sources as solar, geothermal, wind, biomass, hydroelectric, and tidal energy [3].When it comes to renewable energy sources, sunlight stands out as the most promising option due to its abundance, affordability, cleanliness, and lack of pollution [4].
Solar cell technology was first discovered in 1893 by French physicist Alexandre Edmond Becquerel with his discovery of the photovoltaic effect [5].There are now three generations of solar cells manufactured by technology: first, second, and third generation cells [6].The third generation of solar cells are known as dye-sensitized solar cells (DSSC), however a novel type known as quantum dot-sensitized solar cells (QDSSC) has just been developed [7].Because of its low cost, simple production process, ability to employ inexpensive materials, and comparatively high light-toelectricity conversion efficiency, DSSC is a promising technology that has garnered a lot of interest [8].DSSCs are semiconductor devices that can convert sunlight into electrical energy [9].The operation of a DSSC device consists of a dye-sensitive working electrode (TiO2, anode), a comparison electrode (Pt layer, cathode), and an electrolyte that fills the space between the anode and cathode [10].Dyes are important components in DSSCs that are used as sensitizers in harvesting solar energy and converting it into electrical energy.Numerous artificial and natural colors are employed as sensitizers.In addition to synthetic dyes like coumarin, indoline, thiophene, and porphyrin, other natural pigments that can be extracted as dyes include anthocyanins, rubberonoids, and chlorophyll [11].Through the use of Zn (II) metal ions in porphyrin chemical derivatives, a novel dye sensitizer has been created in this study.Chemical sensors and photodynamic treatment are just two of the uses for porphyrins and their derivatives [12].With a high molar absorbance coefficient [13], porphyrin, an artificial chlorophyll [10], can absorb light strongly in the 400-700 nm wavelength range.Moreover, porphyrins have several benefits, including semi-conductivity and the capacity to convert photoconductivity energy into chemical and electrical energy.This is due to the lengthy π-conjugated system in the porphyrin skeleton, which produces a broad range of wavelengths for light absorption [14].
The dye-sensitizer material used in this study is 5,10,15,20-tetraphenylporphyrin (TPP), a porphyrin derivative compound.TPP, a porphyrin derivative that mimics naturally occurring porphyrins, has been applied extensively in scientific studies.TPP is currently used extensively in the photodynamic process for cancer cell therapy; it has never been used in DSSC as a photosensitizer.[15].TPP compounds were utilized in this investigation due to their simplicity in preparation, significant π-conjugation, and effortless functionalization at the meso-phenyl and β-pyrrole positions.[16].Zinc (II) metal was chosen for this investigation due to its high thermal stability and low toxicity.Because of their wide absorption spectrum and ability to boost photosensitizer stability, metal complexes are employed in DSSC [17].Zinc metal has been utilized extensively as a sensitizer, yielding positive outcomes in a variety of compounds, such as zinc methyl 20-bromo-3-devinyl-3hydroxymethylpyropheophorbide-a (ZnChl-2) with an efficiency of 0.81% [18], zinc [5,15dimethylaminophenyl-10,20-(4-carboxyphenyl)Porphyrin] with 3.2% efficiency [13], and ZnT (Mes)P (CN-COOH) (N719) with 5.53% efficiency.[19].
The Adler method is used in this research's synthesis because it is simple, inexpensive, and does not require pressure under nitrogen [20].TiO2 is the semiconductor utilized in this study due to its high electron transport capacity, low toxicity, and good chemical stability [21].N-dimethylformamide (DMF) was used as a solvent in this synthesis because it does not decompose during distillation at low pressure and freely mixes with water, alcohol, ether, ketone, ester, carbon disulfide, and chlorinated and aromatic hydrocarbons.And at high temperatures, DMF solutions have little tendency to hydrolysis.The synthesized compounds were characterized using a UV-Vis spectrophotometer, Fourier Transform infrared (FTIR), and conductometer.

Synthesis of Zn(II)-TPP Complex Compound
The synthesis of the Zn(II)-TPP complex compound was carried out with a mole ratio between ligand and metal of 1:1.A total of 0.025 grams of TPP ligand was dissolved in 10 ml of DMF and put into a 50-ml round-bottom flask.After that, the mixture was heated to 140 ºC while being stirred with a stirrer.The ZnCl2 compound is then added to the reaction mixture and refluxed for six hours after being dissolved in DMF.Subsequently, the Zn(II)-TPP compound mixture was dried and evaporated to a third of its original volume.[22].The measured solid of the Zn(II)-TPP complex compound was dissolved with DMF.Then put into a cuvette and measured the wavelength in the wavelength range of 200-700 nm.
2.2.2 Characterization of Zn(II)-TPP Compunds with FTIR.To identify the functional groups and bonds created between metals and ligands, FTIR measurements were performed.Infrared absorption at wave numbers 4000-300 cm -1 was measured for the solid Zn(II)-TPP complex.

Preparation of Dye-Sensitized Solar Cells (DSSCs)
2.3.1 TiO2 coating on fluorine-doped tin oxide (FTO) glass.FTO glass was first soaked in ethanol for an entire day before being dried to remove any impurities that may have adhered to the glass.For the preparation of TiO2 paste, 20 ml of 98% methanol and 0.5 grams of the TiO2 Degusa P-25 are required.Furthermore, 2 cm x 2 cm area for TiO2 was made using scotch tape and after that the TiO2 suspension was applied to the FTO glass plate using the dip-coating technique.The TiO2 suspension's thickness is maintained with the aid of Scoth tape.This method is finished by dipping the FTO glass into the TiO2 suspension.The TiO2 coating is applied three times by dipping in order to guarantee that the final layer is the same thickness.Before being heated to 450 degrees Celsius for 60 minutes in a furnace, TiO2-coated FTO glass is allowed to dry at room temperature.To make sure the TiO2 layer is evenly distributed in thickness, five measurements are taken using a screw micrometer.Moreover, the TiO2 coating and the weight of the FTO glass are measured [23].

Preparation of the DSSC working electrode.
FTO glass that has been coated with TiO2 was soaked for 2x24 hours in Zn(II)-TPP compound in a petri dish.After completion of soaking, the FTO glass is taken, dried at room temperature, and stored in a closed, dark place to avoid scratches that can damage the TiO2 semiconductor layer.This is done so that it can be used for a long period of time.

Preparation of the DSSC counter electrode.
The conductive side of the FTO glass is to be uniformly shaded with a graphite pencil on the surface before use.After that, a candle flame is used to burn the FTO glass until a carbon layer forms.This heating is done to ensure that the carbon layer adheres to the glass flawlessly and is not easily lost [24].

Preparation of electrolyte solution.
Potassium iodide (KI) 0.5 M, iodine (I2) 0.05 M, and deionized water were needed for the electrolyte solution.To make this electrolyte solution, dissolve 0.83 grams of KI in 1 milliliter of distilled water and use a stirrer to stir evenly.Then, 0.127 grams of I2 were gradually added to the mixture.Next, the solution was mixed with 9 milliliters of distilled water [25].

DSSC tool assembly.
The sandwich technique was used in this study to assemble the DSSC cells.Using a working electrode that has been placed on a flat surface, an electrolyte solution is poured above it and the surface is coated with dye and TiO2.This sandwich technique is created.Additionally, it is attached above the graphite-coated comparison electrode.The DSSC is prepared for testing once the left and right electrode edges are secured with a paper clip to prevent movement.The DSSC circuit is shown in Figure 1.There is a multimeter cable attached to the DSSC that has been made on both sides.The positive pole is linked to the counter electrode, and the negative pole is connected to the working electrode.Following assembly, the DSSC is exposed to direct sunlight and its maximum current and voltage are measured.

Characterization current and voltage using potentiometer.
There is a multimeter cable attached to the DSSC that has been made on both sides.The positive pole is linked to the comparison electrode, and the negative pole is connected to the working electrode.The assembled DSSC is then linked to a potentiometer to measure the minimized and maximized voltage and current.

Result and Discussion
In this research, the TPP compound reacted with Zn(II) metal ions from the ZnCl2 compound to form a Zn(II)-TPP complex compound.The Zn(II)-TPP complex compound is applied as a dye sensitizer on DSSC.The Zn(II)-TPP complex compound that has been formed is characterized using a UV-Vis spectrophotometer, a FTIR spectrophotometer, a conductance test using a conductometer, and measured current and voltage using a multimeter.

Synthesis of Zn(II)-TPP Complex Compound by the Adler Method
The Adler method was used to synthesize Zn(II)-TPP complex compounds.The Adler method at 140 °C is used to create porphyrins and their derivatives [22].In this study, Zn(II) metal ions were synthesized from ZnCl2 compounds with TPP ligands using dimethylformamide (DMF) solvent to create complex compounds.The ligand to metal mole ratio that was employed was 1:1.In a roundbottom flask, 10 ml of DMF were used to dissolve 0.025 grams of TPP.The mixture was then heated to 140 °C and being stirred for a duration of 30 minutes.Following the addition of the ZnCl2 compound, the mixture was continue refluxed for six hours.In the end of the reaction, was obtained a purple-black solution product.After that, the mixture was poured into a glass beaker, and the solvent was extracted by evaporating it to a third of its original volume.The solids are a dark purple colour.In order to demonstrate the complex compound's bonding and properties, the successfully synthesized compound was characterized.The solid of the Zn(II)-TPP complex compound is shown in Figure 2.

Characterization of Zn(II)-TPP Complex Compounds
The formed complex compounds were characterised using UV-Vis spectrophotometer and FTIR spectrophotometer to determine their properties and characteristics.
3.2.1 Characterization of the Zn(II)-TPP complex compound by UV-Vis Spectrophotometer.To find the maximum wavelength shift and maximum wavelength absorption of the Zn(II)-TPP complex compound, a UV-Vis spectrophotometer was utilized for characterization.Two different compounds, TPP and the Zn(II)-TPP complex compound, were used for the measurements in this study.To make sure the complex compound was created by the variation in the maximum wavelength of each component, this is necessary.The results of the Zn(II)-TPP complex compound are shown in Table 1.  1 shows that there is a difference in the maximum wavelength between TPP ligand and the Zn(II)-TPP complex compound.The maximum wavelength of TPP appears in the Soret band region of 410 nm, while the Zn(II)-TPP complex compound appears in the Soret band region of 423 nm.This indicates that the Zn(II)-TPP complex compound has been formed.The TPP ligand shows a Soret band located at a wavelength of 410 nm, which can be attributed to the π-π* electron transition of the conjugated molecule.Compared to the TPP ligand, the Zn(II)-TPP complex compound has a Soret band at a wavelength of 423 nm, which can be inferred from the π-π* ligand-centered (LC) transition of the conjugated TPP ligand due to the presence of Zn(II) metal ions entering the porphyrin ring.It can be seen that in the Zn(II)-TPP complex compound there is a shift when compared to the TPP ligand; this is due to the π-π* transition, which may be caused by the asymmetry of the electric charge density in the porphyrin ring after the complex compound is coordinated with Zn(II) ions.The shift occurs in a wide absorption range because Zn(II) in the d 10 orbital has many electrons, as a result the π-π* transition takes place easily [17].The shift that occurs in the Soret band region can also be caused by the energy gap between HOMO and LUMO, which is small due to the presence of a booster group that can increase HOMO and Zn(II) metal ions that enter the porphyrin ring that can decrease LUMO.So that the energy required by the porphyrin ring to absorb energy becomes smaller in the process of electron excitation [20].This complex compound undergoes a d-d transition, which is indicated by the absorption of wavelengths in the four Q bands.However, this transition is difficult to 6 observe because the ligand has an intense colour that covers the colour of the d-d transition, which is referred to as an overlapping event [26].
3.2.2Characterization Zn(II)-TPP complex using spectrophotometer FTIR.A characterization using a Fourier Transform Infrared (FTIR) Spectrophotometer was carried out to determine the presence of functional groups and bonds formed between ligands and metals.The results of the characterization of the Zn(II)-TPP complex compound are shown in Figures 3 and 4, accompanied by a description in Table 2.   1597.06 cm -1 1600-1300 cm -1 [Reference : [27]; [28]; [29]; [30]] Figures 3 and 4 show the difference in FTIR spectra of TPP ligand and Zn(II)-TPP complex compounds.This shows that the complex compound Zn (II)-TPP has been successfully formed.The complex compound is visible at wave number 324.04 cm -1 .indicating bonding between Zn(II) and TPP.The bond between Zn and N should theoretically appear at wave numbers 325-265 cm -1 [28].The Zn(II)-TPP complex compound's formation can be demonstrated that Zn(II) enter and bind to the four N atoms in the porphyrin ring center.This is because the total energy of the porphyrin molecule in Density Functional Theory (DFT) is -989.57775478esu.which is lower than the Hartree-Fock (HF) theory prediction [31].The predicted bond between Zn metal and TPP ligand is shown in Figure 5. .the FTO glass must first be soaked in ethanol for 24 hours to remove any dirt that may have adhered to it.and then it must be dried.In addition.scotch tape is used to shape the FTO glass into a 2 cm x 2 cm area in order to preserve the suspension's thickness.Next. in order to maximize the adhesion of the TiO2 layer and create a larger surface area.the FTO glass is sanded beforehand.The dip-coating technique is applied to FTO glass to apply TiO2 coating.Using this technique.the glass is submerged in a TiO2 suspension.To make sure that the final TiO2 layer is the same thickness.the TiO2 coating is applied three times.Glass before and after the TiO2 coating is weighed.and the thickness of the layer is measured using a digital micrometer in order to control the thickness of the coating and create a homogenous layer.
3.3.2DSSC electrode manufacturing and cell sequencing.The working electrode was prepared by soaking the TiO2-coated FTO glass for two days in the Zn(II)-TPP complex compound solution.The glass is then kept in a closed.dark area to prevent scratches that could erode the coating.The counter electrode was prepared by sanded the FTO glass first and then uniformly shaded three times in both vertical and horizontal directions using a graphite pencil.Next. a candle flame is used to burn the FTO glass in order to create a black carbon layer that is perfectly adhered to the glass and does not readily evaporate.The working and counter electrodes are shown in Figure 6. 3 Current measurement results against the number of days.Current measurements were carried out for 7 days sequentially.and measurements were also taken on days 14. 21. and 28.In the measurement process.four DSSC cells with different electrode compositions were measured under the same conditions.The 4 DSSC cells are TiO2.TiO2-TPP.TiO2 with a Zn(II)-TPP complex compound.and TiO2 with a mixture of Zn(II) and TPP ions.Measurements are made to determine how much current is generated in each DSSC cell.Measurements are done to find out how much current each DSSC cell produces.In order to ascertain the impact of chemical bonds between complex compounds and ligands on the current generated.measurements were also performed to compare the current generated between the complex compound Zn(II)-TPP and a mixture of metal ZnCl2 and TPP.The current measurement results are shown in Table 3 and Figure 7.  Based on Figure 7. the current generated from the TiO2 compound.TPP ligand.a mixture of Zn(II) metal with TPP. and the Zn(II)-TPP complex compound can be concluded that the Zn(II)-TPP complex compound produces a relatively stable current from days 1 to 4 and increases on days 5 to 7. But on the 14 th to 28 th days.there was a decrease.This also happened to the TiO2 compound.the TPP ligand.and the mixture of Zn (II) metal with TPP. which tended to decrease from day 1 to day 28.This can be caused by the electrolyte.which.the longer it is used.the more exhausted it will be because it evaporates so that the resulting electron transfer cycle becomes less than optimal [24].The mixture of Zn(II) metal and TPP has a lower current than the Zn(II)-TPP complex compound.For the purpose of enhancing the dye-sensitizer's capabilities.a chemical bond between the Zn metal and the TPP ligand has been demonstrated in the Zn(II)-TPP complex compound.The Zn(II)-TPP complex compound also contains conjugate bonds and readily excited free electron pairs.which allow the resulting current to rise.[32].

3.3.4
Voltage measurement against the number of days.The same procedures used for current measurements were used for voltage measurements.which involved taking readings on days 14. 21. and 28 over the course of seven days.Four DSSC cells with varying compositions were measured in the same conditions.The four different DSSC cells are Zn(II)-TPP complex compound-containing TiO2.TiO2-TPP.TiO2.and TiO2 with a combination of Zn(II) and TPP ions.The amount of voltage produced in each DSSC cell is determined by measuring the voltage in relation to the number of days.The voltage measurement results are shown in Table 4 and Figure 8.Based on Figure 8.The Zn(II)-TPP complex compound generates a voltage that is significantly higher than the mixture of Zn(II) metal with TPP.TiO2-TPP.and TiO2.In all these compounds.the voltage value produced tends to be unstable on days 1 through 7 and decreases on days 14 through 21.The electrolyte solution's evaporation may be the cause of this.Furthermore.due to its low stability.the redox component I2 in the electrolyte solution is readily oxidized by air [33].Even though Zn(II) metal is present in both compounds.the Zn(II)-TPP complex compound exhibits a higher voltage value when compared to the mixture of Zn(II) metal.This is because Zn(II) metal and TPP ligand interact in the Zn(II)-TPP complex compound.forming chemical bonds as a result.However.no chemical bond exists in the mixture of metal Zn (II) and TPP ligand.In comparison to TiO2.TiO2-TPP likewise exhibits a higher voltage value.When compared to TiO2 one without any dye.this demonstrates how the dye-sensitizer in the DSSC has an impact on raising the voltage conversion capability [34].From this study, we can see that the highest voltage obtained by Zn-TPP complex is 640 mV.This result is higher if compared by the previous study which is investigate Cu-TMPyP complex and produce the highest voltage 500 mV.On the other side, the highest current obtained by Zn-TPP complex is 32 mA.This result is lower than the previous study (Cu-TMPyP complex) that obtained the highest current about 34 mA.However, both of metal complex Zn-TPP and Cu-TMPyP are potential to be applied as dye sensitizer [35].

Conclusion
Based on the results of research and discussion. it can be concluded that the character of the Zn(II)-TPP complex compound using a UV-Vis spectrophotometer has a maximum wavelength of 423 nm in the Soret band area.In an FTIR spectrophotometer. the bond between Zn and N is formed at wave number 324.04 cm -1 .The conductometer characterization results concluded that the Zn(II)-TPP complex compound is ionic.The presence of the Zn-TPP complex compound as a dye sensitizer is proven to increase the current and voltage of DSSC cells.

Figure 1 .
Figure 1.DSSC tool circuit 2.3.6Current and voltage measurements of DSSC with sunlight irradiation.There is a multimeter cable attached to the DSSC that has been made on both sides.The positive pole is linked to the counter electrode, and the negative pole is connected to the working electrode.Following assembly, the DSSC is exposed to direct sunlight and its maximum current and voltage are measured.

Figure 5 .
Figure 5. Predicted bonding of Zn metal with TPP ligand 3.3 Application of Zn(II)-TPP complex compound as Dye Sensitized Solar Cell (DSSC) 3.3.1 Results of TiO2 coating on FTO glass by dip-coating method.Preparation of FTO glass coated by TiO2. the FTO glass must first be soaked in ethanol for 24 hours to remove any dirt that may have adhered to it.and then it must be dried.In addition.scotch tape is used to shape the FTO glass into a 2 cm x 2 cm area in order to preserve the suspension's thickness.Next. in order to maximize the adhesion of the TiO2 layer and create a larger surface area.the FTO glass is sanded beforehand.The dip-coating technique is applied to FTO glass to apply TiO2 coating.Using this technique.the glass is submerged in a TiO2 suspension.To make sure that the final TiO2 layer is the same thickness.the TiO2 coating is applied three times.Glass before and after the TiO2 coating is weighed.and the thickness of the layer is measured using a digital micrometer in order to control the thickness of the coating and create a homogenous layer.

Figure 6 .
Figure 6.Working electrode and counter electrode 3.3.3Current measurement results against the number of days.Current measurements were carried out for 7 days sequentially.and measurements were also taken on days 14. 21. and 28.In the measurement process.four DSSC cells with different electrode compositions were measured under the same conditions.The 4 DSSC cells are TiO2.TiO2-TPP.TiO2 with a Zn(II)-TPP complex compound.and TiO2 with a mixture of Zn(II) and TPP ions.Measurements are made to determine how much current is generated in each DSSC cell.Measurements are done to find out how much current each DSSC cell produces.In order to ascertain the impact of chemical bonds between complex compounds and ligands on the current generated.measurements were also performed to compare the current generated between the complex compound Zn(II)-TPP and a mixture of metal ZnCl2 and TPP.The current measurement results are shown in Table3and Figure7.

Figure 7 .
Figure 7. DSSC cell current measurement graph against day

Figure 8 .
Figure 8. Graph of DSSC cell voltage measurements against days

Table 1 .
Characterization results of Zn(II)-TPP complex compounds

Table 2 .
Explanation of FTIR spectra data of ligands and complex compounds