3.1. Chemical structure confirmation of the synthesized compound:
3.1.1. FTIR spectra
Fig. 3a showed the FTIR spectrum of DATF. The appearance of characteristic bands at 2850.88cm-1 and 2920.68cm-1 due to the presence of (CH symmetric stretching) and (CH asymmetric stretching), respectively, two vibrational bands at 1470.64cm1, 1392.53cm-1 due to the presence of (CH3 and CH2 asymmetric bending). The appearance of vibrational band at 2521.21 cm-1due to the presence of (NH2 asymmetric stretching) and the appearance of a vibrational band at 1602.79 cm-1 due to (NH2 asymmetric bending).
3.1.2. 1HNMR spectra
Fig. 3b showed 1H-NMR (DMSO-d6) spectrum of DATF. different peaks were observed at δ=1.1ppm (t, 6H, (CH3)2); δ=3.2 ppm (q, 4H, (CH2)2); δ=7.9ppm (s, 2H, NH2).
3.1.2. Performance of PGC
To determination of the voltage-current curve in the PGC, the results of the voltage and current are recorded by putting the PGC in the dark while keeping the circuit open until stable potential is achieved, the Pt electrode is exposed to the light from tungsten lamb. The water filter is placed between the cell and the lamp to cut off the infrared which could negatively affects the cell, and leads to decrease the performance. Upon illumination, the photovoltaic voltage (V) and the photocurrent (i) are generated by the system. After cell charging, the cell parameters such as maximum voltage (Vmax), open circuit potential (Voc), maximum current (imax), equilibrium balance (ieq) or short circuit current (isc) are measured. I-V curve was obtained by registering different data of the voltage by changing the resistance value so that the potential current data are obtained until the value of the zero-current reached. The curve study shows the highest amount by which the cell can be used. The cell is operated at highest power (i.e., power at power point Ppp) at corresponding external load, current (i.e., current at power point ipp) and potential (i.e., potential at power point Vpp) in order to study its performance by monitoring the change in current and potential with time. After establishing the J-V curve and recording the result product the fill factor and conversion efficiency were calculated.
Fill factor is defined as the ratio of the maximum (actual) energy that can be obtained from solar cells to the (theoretic) value Eq (1).
While conversion efficiency known as the ability to convert the amount of forthcoming solar radiation from sun to electricity Eq (2). Both can be expressed as follow:
Where (VPP i.e., potential at power point), (IPP i.e., current at power point) and (A) is the area of Pt electrode.
The PGC charges were studied in a PGC system and the effects of different variables were discussed in order to achieve the highest conversion efficiency, eg; the variation in the pH values of the solution, and variation in the concentration of TBRC, DATF and OX.
3.2. Impact of the variety of pH
Initially, the variation in the pH has been studied in acid and alkali ranges. From this study the highest output of the cell was observed in the acidic medium and that by increasing the acidity the conversion efficiency increases to a certain extent and then decreases thereafter as we go to the alkaline medium.
In previous studies carried out by both Gangotri and Gangotri , Genwa and Chouhan , and Dube et al. , they recorded that the pH of the ideal condition is related with pKa of the reductant, where it is equal to or slightly higher than pKa of the reducing substance. These authors prescribe that the conceivable explanation behind this as the accessibility of the reductant in its in its neutral or anionic form a superior electron donor
From (Table 1 &Figure 4) it was observed that the maximum cell outputs from (photovoltaic power, photoelectric current, power at the power point, fill factor and conversion efficiency) were obtained in an acid medium at pH 2.5 and any increase after that leads to a significant reduce in the cell performance, this may be due to the fact with decrease pH hydrogen ion concentration increase protonation of dye occur with charge transfer and with pH increase complex may join with the oxidized state of the OX reductant, prohibit regeneration of its original state.
3.3. Impact of the variety in the concentration of TBRC
The photochemistry of dye is playing a significant role for understanding the mechanism of electron transfer reactions in photoelectrochemical devices such as PGC. The dye [Ru(bpy)3]2+is considered an ideal dye, as it absorbs both visible and ultraviolet light. UV absorption ranges were observed at 285 nm corresponding to concentrated ligand π-π* transitions and a weak transition around 350 nm (d-d transition) as shown in figure 5 . The results of light absorption in the formation of an excited state have a relatively long lifetime of 890 ns in acetonitrile and 650 ns seconds in water . The excited state unwinds to the ground state by emitting a photon or non- radiative relaxation. Studies have shown that long lifetime of the excited state is due to being triple while the ground state is a single case due to the fact that the molecule allows separation of the charge Most of the time, triple shirt transformations are prohibited, and therefore as slow, Such as all molecular excitatory states. The triple excited state of [Ru(bpy)3]2+ is characterized by strong oxidizing properties and reduction compared to its ground state.
There are numerous derivatives from Ru (bpy)3]2+ [34-38] and most of them have been applied in many different fields, including bio diagnostics, solar cell and organic light-emitting diode.
[Ru(bpy)3] has been applied as a light sensitive dye in solar cells and has proven its efficiency due to its unique properties such as its chemical stability in aqueous solution, strong luminescence, good electrochemical Reversibility, moderate excited-state lifetime, electron transfer reactions, energy and chemical stability [39,40].
(Table 2 & Figure 6) was observed that the maximum cell outputs from (photovoltaic power, photoelectric current, power at the power point, fill factor and conversion efficiency) were obtained at 4.1×10- 4 M and any increase or decrease after that leads to a significant reduce in the cell performance, this may be due to at a low concentration of the dye, there is a restricted number of Photosensitizer atoms expected to ingest photons and give an electron to the Pt electrode in the cell, so there is a decrease in the cell’s output, while higher concentricity of photosensitizers doesn't allow the ideal light intensity to arrive at the particles close to the electrodes and thus, there was relating fall in the power of the cell.
3.4. Impact of the variety in the concentration of DATF
Thirdly, to improve the exhibition of the PGC, IL was applied as electrolytes, these salts have dissolving close toward room temperature and show properties of super cooled liquids whenever warmed over their melting point. PGC containing (DATF) electrolytes, was mix with the ruthenium-based sensitizer (Table 3& Fig. 7) show an effectiveness up to 1.9% at 10.4 mW/cm2 also note that it is relatively stable in the long term. The variation in the concentration of DATF has been studied in low and high ranges. From (Table 3 and Figure 7) it was noted that the maximum cell output from (photoelectric energy, photoelectric current, energy at the power point, filling factor and conversion efficiency) were obtained at concentration of 6 x 10-2M and any increase or decrease after that leads to significant decrease in cell performance, the reason for this may be due to when applying a low concentration there are a limited number of IL molecules available to transfer the electron and solubility of the Ruthenium dye, On the other hand, the high concentration of the IL molecules works to impede the movement of the dye molecules on their way to the electrode, thus resulting in a decrease in the output energy. Also, the reason for the decrease in cell output may be due to potential problems caused by liquid organic electrolytes, such as organic solvent volatilization and leakage that had the effect of limiting long-term performance and practical use of dye-sensitized solar cells (DSSCs).
3.5. Impact of the variety in the concentration of OX
Finally, OX is used in PGC as a (reducing agent) where an electron is lost in the chemical reaction to be received by another electron (oxidizing agent) in the oxidation reduction reaction. The effect of variation in the concentration of OX has been studied in low and high ranges. From (Table 4 &Figure 8) it was observed that the maximum cell outputs from (photovoltaic power, photoelectric current, power at the power point, fill factor and conversion efficiency) were obtained at concentration of 1.9 x 10-3M and any increase or decrease after that leads to Significant decrease in cell performance, this may be due to the fact that at a low concentration of acid, the number of reducing agents’ molecules in the solution decreases, thus the number of electrons that donate to the excited molecules of ruthenium dye decreases. While the high concentration of reducing agents can impede the motion of the ruthenium molecules in the solution from reaching across to the electrodes at the required time, on the other hand, it may also boost back electron transfer from the ruthenium particles to the OX reductant particles.
4. (I–V) characteristics of the cell
The open circuit voltage Voc and short circuit current isc of all these systems were measured with the help of a digital pH meter (keeping the other circuit open) and from a microammeter (keeping the other circuit closed), respectively. The electrical parameters in between these two extreme values (Voc and isc) were determined with the help of a carbon pot (log 470K) connected in the circuit of microammeter, through which an external load in the circuit was applied. After studying a series of variables on the galvanic cells, the highest outputs were recorded for PGC containing (4.1×10-4 M of TBRC, 2.5×10-3M of SDBS, 1.9×10-3M of OX at pH 2.5, Pt electrode of area 0.5cm2 and light intensity=10.4 mW cm–2). The Figure9 shows that potential increases with decreases in the current. The current and power data and curve is also shown in Table 5, and Figure9. The maxima of this curve show the power at power point of the cell and in this system, it is 96.2 µW. And, the current at power point (ipp) and potential at power point (Vpp) for this PGC system is 260 µA and 370 mV, respectively.
5. Recover the amount of energy stored from solar cells in the dark (performance of the cell in the dark)
Initially, the cell is charged in sunlight or any other light source until the cell reaches the highest possible energy then the light source is removed and the cell is placed in the dark. The stored energy is recovered from the cell in the dark as the time it takes for the energy to drop to half of its initial value is called t0.5.
To assess the photo galvanic cell ability to store potential energy, energy recovery of its store in the dark was studied, as it was observed that the value of recovered energy decreased over time until it was fully discharged. During the study, it was observed that the energy does not decrease quickly, but it decreases slowly and sometimes it stabilizes for several minutes, as shown in Figure 10. We note that the energy drops to half (48.1 µW) of its initial value (96.2 µW) at 105 minutes.
6. Stability tests of DATF system
A long-term stability test was performed for PGC with 1.4 × 10-4 M of TBRC as photosensitized with DATF 6×10–2M as IL and 1.9×10–3 M of OX as reductant, at 0.5 active area of Pt and light intensity=10.4 mWcm-2, which showed that the DSSC was stable for 10 day under full sunlight intensity.
The values changed over time for VOC, JSC, FF and η, and are plotted in Figure11. The initial parameters (VOC, JSC, FF, and η) are 650mV, 370µA, 0.4, and 1.9%, respectively. During the test period for initial 3 days all parameters was stable, next three days VOC increased slightly to reach 655, and decreased slightly to 643 mV by the end of the test, which is only 7 mV lower than the initial value (650 mV), indicating the good adsorption stability PGC system.
While ISC exhibited a slightly decreasing to reach 364 mAcm-2 and finally reached 360 µA at the end of the test (10 day) which may originate from slow TBRC degradation. The η of the device slowly degraded to 1.7%, remaining at 90% of the initial value after 10 day of visible-light absorption. The high stability of the cell indicated that the TBRC had excellent stability with IL and that the degradation was insignificant.