Improving Performance of Dye Sensitized Solar Cells Based On Composite Quasi Solid-State Electrolytes of Poly (ionic liquid) / Ionic liquid / TiO2

Improving Performance of Dye Sensitized Solar Cells Based On Composite Quasi Solid-State Electrolytes of Poly (ionic liquid) / Ionic liquid / TiO2

A.Benabdellah* K. Negadi Y.Chaker B. Fetouhi M.Debdab H.Belarbi M. Hatti

Synthesis and Catalysis Laboratory, University of Tiaret, Algeria

Department of Electrical Engineering, Laboratory of L2GEGI, University of Tiaret, Algeria

UDES, Solar Equipments Development Unit, Bou Ismail, Tipaza, Algeria

Corresponding Author Email: 
abdelkader.benabdellah@univ-tiaret.dz
Page: 
270-277
|
DOI: 
https://doi.org/10.14447/jnmes.v24i4.a06
Received: 
21 June 2021
|
Revised: 
19 November 2021
|
Accepted: 
30 November 2021
|
Available online: 
31 December 2021
| Citation

© 2021 IIETA. This article is published by IIETA and is licensed under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/).

OPEN ACCESS

Abstract: 

Composite gel electrolytes of poly(IL) / $\mathrm{IL} / \mathrm{TiO}_{2}$ containing poly [1-(hydroxyethyl)-3vinylimidazolium hydrogen sulfate] (poly $\left[\mathrm{EtOHVIM}^{+}\right]\left[\mathrm{HSO}_{4}{ }^{-}\right]$) as Poly(IL), 1-butyl-3methyl- imidazolium hexafluorophosphate ([BMIM] $\mathrm{PF}_{6}$ ) as IL and Titanium Dioxide $\left(\mathrm{TiO}_{2}\right)$ are prepared for dye-sensitized solar cells (DSSCs), without any volatile organic solvent. The performance of most (DSSCs) based on $\mathrm{TiO}_{2}$ was limited by the low electron mobility within $\mathrm{TiO}_{2}$. To produce a much higher power conversion efficiency performance and better long-term stability of the composite electrolyte without $\mathrm{TiO}_{2}$, a proper amount of $\mathrm{TiO}_{2}$ was added. Overall power conversion efficiency of $7.46 \%$ under simulated AM $1.5$ solar spectrum irradiation for (DSSCs) based on the composite electrolytes were showed. This type of composite electrolytes had long-term stability of the (DSSCs), could overcome the drawbacks of volatile liquid electrolytes, and offer a feasible method to fabricate (DSSCs) in future practical applications.

Keywords: 

poly (IL); Ionic liquid; DSSCs; conversion efficiency, long-term stability

1. Introduction

Development of efficient dye-sensitized solar cells (DSSCs) by simple methodologies offer immense scope and potential in the global strive towards harvesting solar energy [1, 4].

The uses of liquid electrolytes in fabrication for (DSSCs) by traditional process lead to long-term stability problems because of the leakage and volatility [5]. To solve these problems, some solid electrolytes, such as inorganic p-type semiconductors [6, 7] and organic hole-transport materials [8, 12], have been applied in (DSSCs). Solid-state electrolytes could be reduce the leakage problems, enhance the lifetime and sealing cost of (DSSCs) due to it’s a low evaporation rate [13, 15]. It is reported that addition of inorganic nanoparticles into the electrolytes is an effective way to improve the (DSSCs) performance [16, 17]. TiO2 is the most broadly studied (DSSCs) photoanode material where a highest solar conversion efficiency of 11.2% is reported [18]. The poor penetration into mesoporous TiO2 is a major problem influenced on the efficiency of solid state electrolytes, due to lower ionic conductivity, poor electron transfer from dye molecules and recombination faster [19, 21]. Therefore, for combining the best of both sides, the development of quasi-solid-state electrolytes, especially gel polymer electrolytes could resolve the problem of the leakage of liquid electrolyte to some extent, because of their complex preparation process, poor mechanical strength, and low thermal stability, but having limitation area when it comes to using them on a commercial scale [22-25].

Ionic liquid (IL) electrolytes are widely used in dye- sensitized solar cells (DSSCs) in place of organic electrolytes for its unique properties such nonvolatile, negligible vapor pressure, excellent thermal stability, broad electrochemical potential window and high ionic conductivity [25, 27]. Nonetheless, (DSSCs) based on (ILs) are prone to leakage, and in order to overcome this problem, polymer gel electrolytes have been developed for (DSSCs) [28–30]. Although polymer gel electrolyte-based (DSSCs) do not suffer from electrolyte loss, they tend to have low power conversion efficiencies attributed to the lower ionic mobility of ions [31, 32].

Poly (ionic liquid) (poly (IL)) as a new class of polymers which combine both the properties of ionic liquid and polymers have attracted much attention in recent years [33- 35]. Their using for quasi-solid-state (DSSCs) showed high power conversion efficiency and excellent long term stability [36, 37].

In this work, we present an entirely approach to the fabrication of high performance (DSSCs) by using a composite gel electrolyte containing poly (IL) / IL / TiO2 as sensitizer and IZO coated FTO glass substrate as a counter electrode are expected to offer good alternative to the expensive dyes along with improvement in environmental and commercial benefits. The (DSSCs) properties were systematically investigated by the influence of TiO2 content with various amounts. The TiO2 could be well dispersed in poly (IL) / IL to form quasi-solid-state gel electrolytes, without using any volatile organic solvents. Better performance and stability were obtained for the quasi solid- state (DSSCs) with TiO2 compared that without TiO2, which indicating the poly (IL) / IL / TiO2 composite gel electrolytes are a promising candidate for (DSSCs) with good durability. Characterization of electrolytes

The performance of a (DSSCs) is usually influenced by the conductivity of electrolyte, for this, the (DSSCs) based on semi-solid IL electrolytes containing various contents (0 wt%, 1 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2 were prepared respectively. The conductivities of electrolytes containing different content of TiO2 were measured with a CHI660c electrochemical workstation at room temperature, and the results listed in Table 1.

It can be clearly seen that the incorporation of proper amount of TiO2 in the composite electrolytes increases the conductivities. For example, the minimal value of the conductivity of electrolyte it reaches 2.84 × 10-3 S.cm-1 by 0 wt% of TiO2 and increase to the maximum value of 6.72 × 10−3 S.cm−1 by 4 wt% of TiO2. This explained by formation of ion transportation network in the quasi solid-state electrolyte was favors by the addition of TiO2, which improved the movement of free ions in a regular direction [38, 39]. However, the conductivity of the quasi solid-state electrolyte was decrease by the excess of TiO2, indicating potential saturation of ion transport channels formed by the incorporation of TiO2, and the further their addition could block the formed ion transport channels [39]. Therefore, it is not surprising that excess TiO2 resulted in low ionic conductivity.

2. Experimental Procedures

2.1 Reagents and instruments

Zinc acetate dihydrate $\left.\left(\mathrm{Zn}\left(\mathrm{CH}_{3} \mathrm{COO}\right)\right)_{2}, 2 \mathrm{H}_{2} \mathrm{O}\right)$, indium nitrate trihydrate $\left(\operatorname{In}\left(\mathrm{NO}_{3}\right) 3,3 \mathrm{H}_{2} \mathrm{O}\right)$, absolute Ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$, and Monoethanolamine $\left(\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\right)$ pure products of Sigma-Aldrich were used to prepare In-doped $\mathrm{ZnO}$ thin films (IZO). $\mathrm{TiO}_{2}$ nanoparticles (Titanium (IV) oxide, $\mathrm{T}-20 \mathrm{~nm}$, acetic acid silver $\left(\mathrm{C}_{3} \mathrm{H}_{3} \mathrm{AgO}_{3}\right)$ and iodine were obtained from Sigma-Aldrich. N719 dye, Surlyn (ionomer films of $25-\mu \mathrm{m}$ thick) and FTO conducting glass (resistance of $20 \Omega /$ square, transmittance of $85 \%$ ) were purchased from Dalian Rainbow Solar Technology Development Co.Ltd., Dalian, China. All reagents were of analytical grade and were used as received unless otherwise stated. XRD analysis was carried out using a RAD-3X (Rigaku Corporation, Tokyo, Japan) diffractometer with $\mathrm{Cu}-$ $\mathrm{K} \alpha$ radiation. The conductivity of the electrolytes was characterized in an ordinary cell composed of Teflon tube and two identical stainless steel electrodes (diameter of $1 \mathrm{~cm}$) oxide, T-20 nm), acetic acid silver $\left(\mathrm{C}_{3} \mathrm{H}_{3} \mathrm{AgO}_{3}\right)$ and iodine were obtained from Sigma-Aldrich. N719 dye, Surlyn (ionomer films of $25-\mu \mathrm{m}$ thick) and FTO conducting glass (resistance of $20 \Omega /$ square, transmittance of $85 \%$ ) were purchased from Dalian Rainbow Solar Technology Development Co.Ltd., Dalian, China. All reagents were of analytical grade and were used as received unless otherwise stated. XRD analysis was carried out using a RAD-3X (Rigaku Corporation, Tokyo, Japan) diffractometer with $\mathrm{Cu}-$ $\mathrm{K} \alpha$ radiation. The conductivity of the electrolytes was characterized in an ordinary cell composed of Teflon tube and two identical stainless steel electrodes (diameter of $1 \mathrm{~cm}$ ) on a CHI660c electrochemical workstation at room temperature, using the $\mathrm{AC}$ impedance method over the frequency range $0.1 \mathrm{~Hz}-1 \mathrm{MHz}$. The current-voltage (J-V) characteristics were examined by a Keithley model 2400 source meter (Keighley Instruments, Inc. Cleveland, USA) under AM $1.5$ solar spectrum irradiation of $100 \mathrm{~mW} / \mathrm{cm}^{-2}$.

2.2 Preparation of IZO thin films coated FTO Glass substrate

IZO thin films were prepared by the sol-gel dip-coating method using zinc acetate dihydrate and Indium nitrate trihydrate as starting materials followed the literature [28]. For depositing IZO thin films of high physical properties of ZnO, 15% of indium was added to solution. The FTO coated glass substrates were cleaned in an ultrasonic bath in acetone, ethanol and distilled water successively. The IZO layers were deposited by immersing a substrate in the solution for 2 min (Dip-coater KSVDCX2), and then dried at high temperature 300 °C for 4 min in an electric furnace (Nabertherm B-180). The procedure from immersing to drying was repeated 15 times, the IZO films were then annealed at 500 °C for 2h to ensure good electrical contact between the IZO films and the FTO coated glass substrates.

2.3 Synthesis of the poly (IL) and IL

Synthesis and characterization of (poly [EtOHVIM⁺] [HSO4⁻]) as Poly (IL) and [BMIM] PF6 as IL followed the literature [29, 30].

2.4 Preparation of poly (IL)/IL/TiO2 composite electrolytes

The liquidelectrolyte was composed of 1M [BMIM] PF6 (0.1M HF, 0.5 M PF5, 0.4M PCl5), 20 wt% of the poly (IL) (based on the weight of the liquid electrolyte) and different amount (0%, 1%, 2%, 4%, 6%, 8%) of TiO2 was added into the liquid electrolyte and stirred at 60 oC for 4 h, then the homogeneous poly(IL)/IL/ TiO2 electrolytes were obtained.

2.5 Fabrication of DSSCs

The (DSSCs) were fabricated by using a conventional process according: Dye adsorption was carried out by immersing the IZO working electrodes in N719 dye solution (0.5 mM in ethanol) at room temperature for 24 h, then the IZO electrodes were rinsed with ethanol and dried under nitrogen flow. The Ag counter electrode was prepared by dripping a drop 5 mM of acetic acid silver ethanol solution placed onto FTO glass substrate, followed by annealed at 500°C for 15min. (DSSCs) were fabricated by sandwiching poly(IL)/IL/TiO2 electrolytes between dye sensitized IZO working electrode and Ag counter electrode, which were using a sheet of a thermoplastic frame (20-μm thick, Surlyn) as a spacer between the two electrodes. The typical active area of the cells was 0.5 cm2.

3. Results and Discussion

3.1 XRD of IZO coated FTO glass substrate

Figure 1 shows the X‐ray diffraction pattern for the amorphous IZO semiconductors and at layer deposited on FTO glass substrate. The X-ray diffraction investigations showed that the FTO glass was highly textured, with its (200) axis being perpendicular to the substrate, as one can see in Figure 1.

To better distinguish the patterns acquired from the grown IZO particles, offset (incidence angle close, but slightly different from theta) and grazing incidence (incidence angle= 5°) geometries were used, and the acquired patterns. The XRD pattern of the IZO sample showed a smooth surface composed of small grains (Figure 1). For this film, the (110) peak at 33.54° is dominant. This preferential (110) orientation is unique among the reported high-quality coated IZO films, of which the majority exhibited a (101) texture [31, 32]. It should be noted that, apart from the solution composition and deposition conditions, the use of a seeding layer can also influence the texture of the film [33].

Figure 1. XRD spectra of IZO and IZO coated FTO glass substrate

3.2 Morphological properties of IZO coated FTO glass substrate

Properly cross-sections images of the two films (FTO coated glass substrate and IZO coated FTO glass substrate) were performed with a Tescan Lyra3 FEG-SEM combining high resolution and high- performance Ga focused ion beam (FIB) quired for optical applications (Figure 2).

Figure 2. Cross-sections images of FTO coated glass substrate and IZO coated FTO glass performed by FEG-SEM

The thickness observed by FEG-SEMf of the two films is homogenous and surfaces are very smooth. In the two samples, similar rough interfaces between the IZO thin film and the FTO coated glass substrate are observed. However the IZO thin film appears to be denser than that of FTO coated glass substrate. The deposited films present more porosity near the surface. The texture of the film cross- section is finer for IZO.

3.3 Characterization of electrolytes

The DSSCs based on semi-solid IL electrolytes containing various contents (0 wt%, 1 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2 were prepared respectively. All the electrolytes are quasi-solid-state gels at room temperature. The performance of a DSSC is usually influenced by the conductivity of electrolyte. The conductivities of electrolytes containing different content of TiO2 were measured with a CHI 660c electrochemical workstation at room temperature, and the results listed in Table 1.

Table 1. Photovoltaic performance parameters of the DSSCs based on electrolytes content (0 wt%, 1wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2 measured under AM 1.5 solar spectrum irradiation of 100 mW cm-2

Cells content

Conductivity

Jsc

Voc

FF

$\eta$

TiO2 (wt%)

(10-3 S. cm-1)

(mA. cm-1)

(mV)

 

(%)

0 wt%

2.84

7.32

0.96

0.72

1.24

1 wt%

3.46

8.86

1.03

0.81

2.48

2 wt%

4.21

15.96

1.13

0.85

5.51

4 wt%

6.72

18.84

1.16

0.89

7.46

6 wt%

6.16

11.92

1.11

0.83

4.42

 8 wt%    

5.12

7.86

0.99

0.76

3.12

It can be clearly seen that the incorporation of proper amount of $\mathrm{TiO}_{2}$ in the composite electrolytes increases the conductivities. For example, the minimal value of the conductivity of electrolyte it reaches $2.84 \times 10^{-3} \mathrm{S.cm}^{-1}$ by 0 wt $\%$ of $\mathrm{TiO}_{2}$ and increase to the maximum value of $6.72 \times$ $10^{-3} \mathrm{~S}^{-1} \mathrm{~cm}^{-1}$ by $4 \mathrm{wt} \%$ of $\mathrm{TiO}_{2}$. The formation of ion transportation network in the quasi solid-state electrolyte was favors by the addition of $\mathrm{TiO}_{2}[34,35]$. However, the conductivity of the quasi solid-state electrolyte was decrease by the excess of $\mathrm{TiO}_{2}$, indicating potential saturation of ion transport channels formed by the incorporation of $\mathrm{TiO}_{2}$, and the further their addition could block the formed ion transport channels [35].

3.4 Characterization of DSSCs

Photocurrent density-voltage characteristics of (DSSCs) based on electrolytes containing different content (0 wt%, 1 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2 which were measured under AM 1.5 solar spectrum irradiation of 100 mW.cm-2 are shown in Fig. 3.

The data of the open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and the photoelectric conversion efficiency ($\eta$) are also summarized and listed in Table 2. Electrolyte in (DSSCs) without TiO2 shows a (Jsc) of 5.86 mA cm-2, (Voc) of 0.68 mV, (FF) of 0.76, and ($\eta$) of 1.24% respectively. the maximum values of (Jsc), (Voc) and ($\eta$) are obtained by increasing the content of TiO2 to 4 wt%, but these values decrease with additional TiO2 . The best performance of (DSSCs) was obtained from electrolyte which containing 4 wt% TiO2 which shows a maximum photoelectric conversion efficiency of 7.46%. The performance of the (DSSCs) devices decrease with the excess addition of TiO2 into the (IL) based gel electrolyte, probably due to the high viscosity of the gel electrolyte and the aggregation of $\mathrm{TiO}_{2}$ which blocked the charge transfer in the gel electrolyte.

Figure 3. J-V curves of DSSCs with electrolytes content (0 wt%, 1wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2 under simulated AM 1.5 solar spectrum irradiation at 100 mW cm−2

The higher charge density in the (DSSCs) might be due to the higher thermal stability of poly (IL), which will be beneficial for durable high temperature (DSSCs). It should be noted that the efficiency of the (DSSCs) is critically dependent on the ion conductivity and diffusion coefficient of the anions in (IL), which the $\pi-\pi$ stacked imidazolium rings of the Poly(IL) provide the charge transport from the counter electrode to the photoanode [40, 41].

3.5 Incident photo-to-current conversion efficiency

Figure 4 shows the incident photo-to-current conversion efficiency (IPCE) curves of cells content (0 wt%, 1 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2. Cell content (4 wt%) have high (IPCE) value as 78.8% at 550 nm was obtained, which is higher than that of Cell content (0 wt%) which have (16.8%), Cell (1 wt%) (36.2%), Cell (2 wt%) (54.6%), Cell (6 wt%) (38.3%), and Cell (8 wt%) (19.7%) respectively. The photoelectric conversion efficiency of the (DSSCs) is consistent with the (IPCE) values.

Figure 4. IPCE curves of DSSCs based on gel electrolytes content (0 wt%, 1wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2

These indicate that the weak interaction force between the alkyl chain of the imidazolium cation and its flexibility enables the electron to be easily transferred in the electrolyte [40]. Thus, the ionic conductivity and diffusion coefficient of PF6- in the poly(IL) based gel electrolyte still reached reasonable values.

3.6 Electrochemical impedance spectroscopy (EIS) measurements

were investigated by the electrochemical impedance spectroscopy (EIS) technique. The (EIS) Nyquist plot of cells content (0 wt%, 1 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2 which measured at -0.7V bias under dark environment were shown in Fig. 5.

Figure 5. EIS Nyquist plots of cell content (0 wt%, 1wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2

In the (EIS) spectra of (DSSCs) from high to low frequency three semicircles can be seen correspond to the charge transfer resistance at the counter electrode (R1), the resistance of IZO coated FTO glass substrate, TiO2 doped electrolyte interface (R2), and the Warburg diffusion process (Rdiff) of PF5/PF6 in the electrolyte respectively [42, 43]. The overall series resistance was coded as (Rs). The values corresponding of the resistance shown in Fig.5 are listing in Table 2.

Table 2. Electrochemical impedance spectroscopy results of cells content (0 wt%, 1wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2

 Cells content

R1

R2

Rdiff

TiO2 (wt%)

(Ω)

(Ω)

(Ω)

0 wt%

12.24

10.24

28.18

1 wt%

7.12

5.86

8.78

2 wt%

5.56

2.31

4.64

4 wt%

3.86

1.89

2.64

6 wt%

6.26

2.94

9.14

8 wt%

7.89

6.16

21.04 

The maximum values of (R1) was obtained by increasing the content of TiO2 to (8 wt%), but the value decrease with additional TiO2. This phenomenon is in good coordination With the reversed order observed for the ( $\eta$ ) of the (DSSCs). The trends of $\left(R_{2}\right)$ and ( $\left.R_{\text {diff }}\right)$ are similar with $\left(R_{1}\right)$, the minimum resistance values of $1.89$ and $2.64 \Omega$ were shown in cell content $(4 \mathrm{wt} \%)$ of $\mathrm{TiO}_{2}$. These results conforming that the charge transport at the IZO /electrolyte interface increased, as well as the enhancement of transport of $\mathrm{PF}_{5}-/ \mathrm{PF}_{6}-$ ions in the electrolyte by the addition of proper content of $\mathrm{TiO}_{2}$, which reducing the charge recombination at photoanode /electrolyte interface due to the enhanced charge transport properties of an $\mathrm{PF}_{5}-\mathrm{PF}_{6}{ }^{-}$redox couple in the gel electrolyte.

3.7 Intensity-modulated photocurrent and photovoltage spectroscopy measurements

To further investigate the $\mathrm{TiO}_{2}$ content effect on the electron transport and charge recombination in the DSSCs, plots of intensity- modulated photocurrent spectroscopy (IMPS) (Figure 6.A) and photovoltage spectroscopy (IMVS) (Figure 6.B) of cells contents $(0$ wt $\%, 1 w t \%, 2$ wt $\%, 4$ wt $\%$, $6 \mathrm{wt} \%, 8 \mathrm{wt} \%)$ of $\mathrm{TiO}_{2}$ were conducted. The transit time $\left(\tau_{\mathrm{d}}\right)$ and electron lifetime $\left(\tau_{n}\right)$ can be calculated using the follow equations:

$\tau_{d}=\left(2 \pi f_{\min }(I M P S)\right)^{-1}$                   (1)

$\tau_{n}=\left(2 \pi f_{\min }(I M V S)\right)^{-1}$                   (2)

Where: $f_{\min }(I M P S)$ and $f_{\min }(I M V S)$ are the frequencies at the minimum imaginary component in the (IMPS) and (IMVS) plots [38].

Figure 6.A. IMPS plots of cell content (0 wt%, 1wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2

The electron lifetime and transit time of cells contents (0 wt%, 1wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2 were listed in Table 3. The longest electron lifetime of 114.89 ms and the shortest transit time of 0.34 ms were showed by cell content (4 wt%) of TiO2. the collection of electrons were favouring by a long (τn) before they recombine in the cells [39], and indicating more electrons surviving from the back reaction which results in high photocurrent [38, 40].

Figure 6.B. IMVS plots of cell content (0 wt%, 1wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2

To collect the charge injected by dye in (DSSCs) [41], it is important the $\left(\tau_{\mathrm{d}}\right)$ is much shorter than $\left(\tau_{\mathrm{n}}\right)$ which confirming our results. The performance of (DSSCs) is improved by increasing the content of $\mathrm{TiO}_{2}$ until it reaches $4 \mathrm{wt} \%$ which give a tendencies of $\left(\tau_{\mathrm{n}}\right)$ and $\left(\tau_{\mathrm{d}}\right)$ in good agreement.

Table 3. IMPS/IMVS parameters of cells content (0 wt%, 1wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%) of TiO2

Cells content

fmin (IMPS)

fmin (IMVS)

$\tau_{d}$

$\tau_{n}$

TiO2 (wt%)

(Hz)

(Hz)

(ms)

(ms)

0 wt%

8.76

18.22

16.55

13.72

1 wt%

26.1

6.24

9.86

38.25

2 wt%

55.37

3.12

5.74

82.61

4 wt%

76.14

0.86

0.34

114.89

6 wt%

38.94

4.48

4.32

50.59

8 wt%

18.22

10.23

12.43

21.06

Compared with Cell content (0 wt%) of TiO2, composite gel electrolytes of (DSSCs) are enough to favors electron transport through a longer distance with less diffusive hindrance which leads finally to enhanced photoelectric conversion efficiency [42].

3.8 Efficiency for the DSSCs aging tests

For the practical applications of (DSSCs), the long-term stability still as major problem. So we have investigated the long-term stability of (DSSCs) via an accelerating aging test of the sealed devices [49]. The values of the total efficiencies of cell content (0 wt%, 4 wt%, 8 wt%) of TiO2 measured on the first day are shown in Fig.7. The early stage of long-term stability testing of the efficiency of all the three devices was enhanced by the increased of the dye regeneration rate which enhanced the (Jsc) of (DSSCs) [47, 48]. As shown in Fig. 7, after 1600 h Cells content (4 wt%) and (8 wt%) of TiO2 were retains 98.5% and 94% of their initial efficiency respectively, under the same conditions cell content (0 wt%) of TiO2 maintained 85% of the initial efficiency.

Figure 7. Time-course variation of the normalized efficiency for the DSSCs with cells content (0 wt%, 4 wt%, 8 wt%) of TiO2 during accelerated aging tests at 60 °C of

By addition of TiO2 the long-term stability of (DSSCs) is greatly improved, probably due to the gel network hindered the leakage in the release of ionic liquid component from the composite electrolyte, it should be noted that both the poly (IL) electrolytes exhibit superior long-term stability than the ionic liquid electrolyte because the gel network hindered the leakage of the liquid electrolyte effectively [40]. The long-term stability of cell content (8 wt%) is lower than the cell content (4 wt%) of TiO2, probably due to the aggregation of TiO2 in the electrolyte [42]. All these results have excellent practical stability of the (DSSCs) based on this type of gel electrolyte containing proper content of TiO2.

4. Conclusion

Indium doped $\mathrm{ZnO}$ (IZO) coated FTO Glass substrates exhibited a particularly high transparency. X-ray diffraction investigations showed that the FTO glass was highly textured, and IZO films coated FTO glass substrate prepared high-quality. Poly (IL)/ $/ \mathrm{T} / \mathrm{TiO}_{2}$ composite gel electrolyte have been prepared for quasi-solid state (DSSCs) with various amounts of $\mathrm{TiO}_{2}$. The incorporation of proper amount of $\mathrm{TiO}_{2}$ in the composite electrolytes increased the conductivities, this explained the enhancement in the charge transport at the $\mathrm{TiO}_{2}$ /electrolyte interface, as well as the enhancement of transport of $\mathrm{PF}_{5}-\mathrm{PF}_{6}^{-}$ions. The composite electrolytes in (DSSCs) with proper $\mathrm{TiO}_{2}$ show higher open circuit voltage (Voc), short circuit current density (Jsc), photoelectric conversion efficiency ( ), and better long-term stability compared with the (DSSCs) based on electrolyte without $\mathrm{TiO}_{2}$. The maximum efficiency of the (DSSCs) based on composite electrolyte showed high value $7.46 \%$ in 4 wt $\%$ of $\mathrm{TiO}_{2}$ under AM $1.5$ solar spectrum irradiation. All the obtains results in the present work have excellent practical stability of the (DSSCs) based on this type of gel electrolyte containing proper content of $\mathrm{TiO}_{2}$ which could overcome the leakage problem of liquid electrolytes.

Nomenclature

[BMIM] PF6

1-butyl-3-methyl-imidazolium hexafluorophosphate

DSSCs

dye-sensitized solar cells

EIS

Electrochemical impedance spectroscopy

FTO

Fluorine Tin Oxide

FIB

focused ion beam

FEG-SEM

Field Emission-Gun-Scanning Electron Microscopy

Jsc

short circuit current density

IMPS

intensity-modulated photocurrent spectroscopy

IMVS

Intensity-modulated photovoltage spectroscopy

IPCE

Incident photo-to-current conversion efficiency

IZO

Indium Zinc Oxide

PCl5

Phosphorus pentachloride

R1

Resistanceat the counter electrode

R2

Resistance of electrolyte interface

Rdiff

Resistancediffusion process

TiO2

Titanium dioxide

Voc

Open circuit voltage

τd

The transit time

τn

Electron lifetime

$\eta$

Conversion efficiency

  References

[1] M.S. Su’ait, M.Y.A. Rahman, A. Ahmad, (2015).Review on polymer electrolyte in dye-sensitized solarcells (DSSCs). Sol. Energy, 115, 452–470.

[2] M. Laura Parisi, S. Maranghi, A. Sinicropi, R. Basosi,Development of Dye Sensitized Solar Cells: A LifeCycle Perspective for The Environmental and MarketPotential Assessment of a Renewable EnergyTechnology, Journal of New Materials forElectrochemical Systems, 7(2013)143-148,DOI: https://doi.org /10.18280 /ijht .310219.

[3] K. Mohan, A. Bora, B.C. Nath, P. Gogoi, B.J. Saikia,S.K. Dolui, (2016). A highly stable and efficient quasisolidstate dye sensitized solar cell based onPolymethylmethacrylate (PMMA)/PolyanilineNanotube (PANI-NT) gel electrolyte. Electrochim.Acta, 222, 1072–1078.

[4] S.S. Yuan, Q.W. Tang, B.L. He, P.Z. Yang, (2014).Efficient quasi-solid-state dye-sensitized solar cellsemploying polyaniline and polypyrrole incorporatedmicroporous conducting gel electrolytes.J. PowerSources, 254, 98–105.

[5] R.H. Lee, T.F. Cheng, J.W. Chang, Ho, J.H.(2011).Enhanced photovoltaic performance of quasi-solid-statedye-sensitized solar cells via incorporatingquaternized ammonium iodide-containing conjugatedpolymerinto PEO gel electrolytes. Colloid Polym.Sci,289, 817–829.

[6] L. Shuang, L. Liu, M. Qingzhuo Du Zeyuan, F. Yuhang,Z.Yajun, L. Xiaowei, Z. Xiaohui, Preparation ofPbS/NiO Composite Photocathode and TheirApplications in Quantum Dot Sensitized Solar Cells,Journal of New Materials for Electrochemical Systems,23(2020)7-12.

DOI: https://doi.org/10.14447/jnmes.v23i1.a02.

[7] H.A. Deepa, G.M. Madhu, B.E. Kumara Swamy, J.Koteswararao, Estimation of Photovoltaic Properties of ZnO nanoparticles and CeO2- ZnO composite and Electrochemical Determination of Adrenaline Employing Voltammetry Studies, Journal of New Materials for Electrochemical Systems, 23(2020)71-77. DOI: https://doi.org/10.14447/jnmes.v23i2.a03.

[8] Q.H. Li, X.X. Chen, Q.W. Tang, H.Y. Cai, Y.C. Qin,B.L. He, M.J. Li, S.Y. Jin, Z.C. Liu, (2014), Enhancedphotovoltaic performances of quasi-solid-state dyesensitized solar cells using a novel conducting gelelectrolyte. J. Power Sources, 248, 923–930.

[9] K. Tennakone, G.R.R.A. Kumara, A.R. Kumarasinghe,K.G.U. Wijayantha, P.M. Sirimanne, A dye-sensitizednano-porous solid-state photovoltaic cell.Semicond. Sci. Technol.1995,10, 689–1693.

[10] G. Kumara, A. Konno, K. Shiratsuchi, J. Tsukahara andK.Tennakone, Chem Mater, 2002, 14, 954−955.

[11] K. Tennakone, G. Senadeera, D. De Silva andI.Kottegoda, Appl Phys Lett, 2000, 77, 2367−2369.

[12] G.R.R. Kumara, A. Konno, G.K.R. Senadeera, P.V.VJayaweera, D.B.R.A. De Silva, K Tennakone, Dye-sensitized solar cell with the hole collector p-CuSCNdeposited from a solution in n-propyl sulphide.Sol.Energy Mater. Sol. Cells.2001,69, 195–199

[13] C. S. Karthikeyan, H. Wietasch and M. Thelakkat, AdvMater, 2007, 19, 1091−1095.

[14] U. Bach, D. Lupo, P. Comte, J. Moser, F. Weissörtel, J.Salbeck, H. Spreitzer and M. Grätzel, Nature, 1998,395, 583- 585.

[15] A. Sepehrifard, B. A. Kamino, T. P. Bender and S.Morin, ACS Appl Mater Interfaces, 2012, 4,6211−6215

[16] M. Wang, X. Pan, X. Fang, L. Guo, C. Zhang, Y.Huang, Z. Huo and S. Dai, J Power Sources, 2011, 196,5784–5791.

[17] B. O’Regan, D.T. Schwartz, Large enhancement inphotocurrent efficiency caused by UV illumination ofthedye-sensitized heterojunction TiO2/RuLLNCS/CuSCN: Initiation and potential mechanisms.Chem. Mater.1998,10, 1501–1509.

[18] S.E. Shaheen, C.J. Brabec, N.S. Sariciftci, F. Padinger,T.Fromherz, J.C. Hummelen, (2001). 2.5% efficientorganic plastic solar cells. Appl. Phys. Lett,78, 841.

[19] N.F. Zain, N.A. Dzulkurnain, A. Ahmad, F. Salleh, N.S.Mohamed, Polymer Electrolytes Based on NovelPoly(Ethyl Methacrylate-co-Deproteinized NaturalRubber) for dye Sensitized Solar Cell Application,Journal of New Materials for Electrochemical Systems,22 (2019) 65-69.DOI: https://doi.org/10.14447/jnmes.v22i2.a01

[20] J.X. Zhao, S.G. Jo, D.W. Kim, (2014), Photovoltaicperformance of dye-sensitized solar cells assembledwith electrospunpolyacrylonitrile/silica-based fibrouscomposite membranes. Electrochim. Acta,142, 261–267.

[21] S.H. Park, D.H. Won, H.J. Choi, W.P. Hwang, S.I.Jang, J.H. Kim, S.H. Jeong, J.U. Kim, J.K. Lee, M.R.Kim, (2011), Dye-sensitized solar cells based onelectrospun polymer blends as electrolytes. Sol. EnergyMater. Sol. Cells,95, 296–300.

[22] A. Benabdellah, H. Belarbi, H. Ililkti. (2018). Dopingof PANI by ionic liquids and its applications in thejunctions. Book.

[23] A. Benabdellah, H. Belarbi, H. Ilikti, T.Benabdallahand M. Hatti. (2015). Magnetic Properties ofPolyaniline/ZFe2O4 Nanocomposites Synthesized inCTAB as Surfactant and Ionic Liquid. TensideSurfactants Detergents, Vol 52, 431-431.

[24] G. Wang, L. Wang, S. Zhuo, S. Fang and Y. Lin, ChemCommun(2011), 47, 2700–2702.

[25] Y. Zhou, W. Xiang, S. Chen, S. Fang, X. Zhou, J. Zhang and Y. Lin, ChemCommun, (2009), 3895-3897.

[26] Y. Zhang, J. Zhao, B. Sun, X. Chen, Q. Li, L. Qiu andF.Yan, Electrochim Acta, 2012, 61, 185-190.

[27] A. Benabdellah, M. Debdab, Y. Chaker, B. Fetouhi, M.Hatti. (2019). Efficiency of Polyaniline/(ZnO, Cds)Junctions Doped by Ionic Liquid in PhotovoltaicProperties. International Conference on ArtificialIntelligence in Renewable Energetic Systems. IC-AIRES2019.

[28] G. Wang, L. Wang, S. Zhuo, S. Fang and Y. Lin, ChemCommun 2011, 47, 2700–2702.

[29] Y. Zhang, J. Zhao, B. Sun, X. Chen, Q. Li, L. Qiu andF.Yan, Electrochim Acta, 2012, 61, 185-190.

[30] Y. Zhou, W. Xiang, S. Chen, S. Fang, X. Zhou, J.Zhang and Y. Lin, Chem Commun, 2009, 3895-3897.

[31] A. Mahdjoub, S. Benzitouni and M. Zaabat. (2018).High transparency of ZnO: In coated glass substrates. Journal of New Technology and Materials (JNTM). Vol. 08, N°01, 31-36

[32] B. Fetouhi, H. Belarbi, A. Benabdellah, S. Kasmi-Mir,G.Kirsch. (2016), Extraction of the heavy metals fromthe aqueous phase in ionic liquid 1-butyl-3-methylimidazolium hexafluoro-phosphate by N-salicylideneaniline. J. Mater. Environ. Sci. 7 (3)746-754.

[33] Y. Chaker, The influence of chloride and hydrogensulfate anions in two polymerised ionic liquids based on the poly(1-(hydroxyethyl)-3-vinylimidazolium cation,synthesis, thermal and vibrational studies. EuropeanPolymer Journal. Vol 108, (2018) 138-149

[34] BC. Jiao, XD. Zhang, CC. Wei (2011), Effect of aceticacid on ZnO: in transparent conductive oxide preparedby ultrasonic spray pyrolysis. Thin Solid Films520:1323–1329. doi:10.1016/j.tsf.2011.04.152

[35] H. Gómez, A. Maldonado, R. Asomoza, (1997),Characterization of indium-doped zinc oxide filmsdeposited by pyrolytic spray with different indiumcompounds as dopants. Thin Solid Films 293:117–123.doi:10.1016/S0040-6090(96)09001-3

[36] J. Wienke, AS. Booij, (2008), ZnO: in deposition byspray pyrolysis — Influence of the growth conditionson the electrical and optical properties. Thin Solid Films516:4508–4512. doi:10.1016/j.tsf.2007.05.078

[37] S. Hyung Kang, K. Jae-Yup, K. Yukyeong ,K. HyunSik , S.Yung-Eun, Surface Modification of StretchedTiO2 Nanotubes for Solid-State Dye-Sensitized SolarCells. J. Phys. Chem. C 2007, 111, 26, 9614-9623

[38] J. Bisquert. Comment on Diffusion Impedance andSpace Charge Capacitance in the Nanoporous Dye-Sensitized Electrochemical Solar Cell and ElectronicTransport in Dye-Sensitized Nanoporous TiO2 SolarCells- Comparison of Electrolyte and Solid-StateDevices. J. Phys. Chem. B 2003, 107, 48, 13541-13543.

[39] H.J. Lee, K. JinLee, K.Mi-Ra, W. S. Shin, S. HoJin, K.Hoon Kim, D. Won Park & S.Wook Park, (2011),Influence of Ionic Liquids in Quasi-Solid StateElectrolyte on Dye-Sensitized Solar Cell Performance.Journal Molecular Crystals and Liquid Crystals.Volume 462, 75-81.

[40] K. Jeong-Hwa, J. Kun-Ho, S.Shi-Joon, H. Dae-Kue.(2017), Enhanced Performance of Dye-Sensitized SolarCells Based on Electrospun TiO2 Electrode. Journal ofNanoscience and Nanotechnology, Vol 17, 8117-8121.

[41] O. Borodina and T. R. Jow, Quantum ChemistryStudies of the Oxidative Stability of Carbonate, Sulfoneand Sulfonate-Based Electrolytes Doped with BF4-,PF6-Anions. J.Electrochemical Society. 2011 vol 33(2011) 77-84.

[42] B. Lin, H. Shang, F. Chu, Y. Ren, N. Yuan, B. Jia, S.Zhang, Y. Wei, X. Yu and J. Ding, ElectrochimicaActa, 2014, 134, 209– 214.

[43] Y. Wang, J. Zhang, X. Cui, P. Yang and J. Zeng,Electrochim Acta, 2013, 112, 247-251.

[44] S. Sharma, O. K. Varghese, G. K. Mor, T. J. LaTempa,N. K. Allam and C. A. Grimes, J Mater Chem, 2009,19, 3895-3898.

[45] F. Fabregat-Santiago, J. Bisquert, G. Garcia-Belmonte,G Boschloo and A. Hagfeldt. (2005). Solar EnergyMaterials and Solar Cells, 87, 117-131.

[46] W. Zhang, C. Yuan, J. Guo, L. Qiu, F. Yan. (2014).ACS Appl Mater Interfaces, 6, 8723−8728.

[47] X. Chen, J. Zhao, J. Zhang, L. Qiu, D. Xu, H. Zhang, X.Han, B. Sun, G. Fu, Y. Zhang and F. Yan, J MaterChem, 2012, 22, 18018–18024.

[48] P. Wang, S. M. Zakeeruddin, J. E. Moser, M. K.Nazeeruddin, T. Sekiguchi and M. Grätzel, Nat Mater,2003, 2, 402–407.