**4. Effect of CNT on the cell performance of DSSC**

#### **4.1 Effect of CNT based photoanode on the cell performance of DSSC**

As mentioned earlier (in Section 3.1.), adding CNT nanoparticles into mesoporous structure provides a strong light-harvesting capability and a large surface area for high-efficiency DSSC. Mesoporous semiconductor materials anchor on the long tubular CNT's outer surface and this assembly ensure efficient electron transport through CNTs. CNT improves the electron transport and increases the coating's thickness; thus, dye building on the anode material increase. CNT results in gains in the photocurrent without compromising the electron injection to the electrode.

From the previous discussion (Section 3.1.), CNT can be used either CNT/semiconductor material composite photoanode or counter electrode. For CNT-based photoanode for different types of dyes, such as metal complex dye sensitizer, natural dye sensitizer has been explored for DSSC operation.

**Figure 10.** *CNT based counter electrode for DSSC.*

crystalline structure, there were no grain boundaries, which provides a smooth surface for electron transportation [38]. Zhu et al. sensitized rice grain-shaped TiO2/MWCNT composite by electrospinning process. Due to the single crystalline

composite, DSSC showed a 32% improvement in cell performance with 0.2 wt.%

In recent years, carbon-based materials in ionic liquids have been investigated as

a potential alternative for traditional liquid electrolytes for DSSC application. An effective electrolyte has low viscosity, low vapor pressure, high diffusion coefficient, high electrochemical, and thermal stability. Conventional liquid redox electrolyte has low viscosity and high diffusion coefficient. However, liquid redox electrolyte uses a volatile solvent, which causes a problem in the commercialization

of DSSC, such as cell leakage of electrolyte, performance degradation, high-

temperature instability, and pressure build-up after in the fabricated cell due to the volatile solvent. Also, liquid electrolyte creates obstacles for the flexible structure and large-scale solar cell. Quasi-solid-state electrolytes based on ionic liquids can easily solve the drawbacks of liquid electrolyte efficiently. Organic hole conducting materials, p-type inorganic semiconductors, or different nano-components (i.e., graphene, CNTs) were diffused into ionic liquids to the sensitized quasi-solid-state electrolyte for DSSC application. **Figure 9** shows a basic schematic diagram of a

In recent years, carbon-based materials, such as graphite, carbon black, and carbon nanotubes, have been studied to replace traditional platinum (Pt) counter

structure and high surface area of the rice grain-shaped TiO2/MWCNT

MWCNT [39].

**3.2 CNT based electrolyte in DSSC**

*Solar Cells - Theory, Materials and Recent Advances*

CNT based electrolyte for DSSC.

**3.3 CNT based cathode in DSSC**

**Figure 9.**

**392**

*CNT based electrolyte for DSSC application.*

**Figure 11.** *SEM of the cross-section CNT based counter electrode [43].*


to obtain a fixed percentage of MWCNT/TiO2 composite. The MWCNT/TiO2 composites were tape cast on FTO glass substrate. The concentration of MWCNTs was varied in the range of 0–0.250 wt. %. The fabricated photoanodes were soaked in a 0.5 mM ethanolic solution of N719 sensitizer. They were increasing the percentages of MWCNTs in the MWCNT/TiO2 composite, which results in a slight improvement in dye loading (from 0.010–0.020%). In comparison, the average number of dye mole per volume unit improved almost 3.5 times for the 0.25 wt.% MWCNT/ TiO2film than the pure TiO2film. However, this chemisorption of dye multilayers are detrimental for overall cell efficiency: for optimum cell efficiency, the dye should be chemisorbed in a closely packed monolayer. **Figure 13** illustrates the SEM

*I-V characteristics of pristine TiO2, chemically modified CNT/ TiO2 and O2 plasma treated CNT/TiO2*

*Improvement of Efficiency of Dye Sensitized Solar Cells by Incorporating Carbon Nanotubes*

From **Table 2**, optimized concentration (0.010–0.020 wt.%) of MWCNTs based

The integration of MWCNTs improved the cell efficiency of the DSSC by devel-

oping a special charge carrier transport channel that is distributed uniformly throughout the TiO2 semiconductor. Cell efficiency of all concentrations of MWCNT incorporated by TiO2 is higher than that of the without MWCNT incorporated by TiO2. The concentration of the MWCNT from 0.000 wt. % to 0.015 wt. %, cell efficiency has improved dramatically (From **Table 3**). The optimum concentration is 0.015 wt. % MWCNTs have a maximum cell efficiency of 1.653%, whereas for without MWCNT integrated TiO2, cell efficiency is 0.921%. After achieving the best possible combination, further increasing the concentration of MWCNT leads to a negative effect on cell parameters such as Isc, Voc, and FF.

TiO2 photoanode significantly increases the overall cell conversion efficiency. Introducing a reflection layer into the cell increases the electron lifetime and decreases recombination, leading to improved overall cell performance and

Not only DSSC sensitized with metallic dye, but also DSSC sensitized with natural dye shows similar characteristics to the concentration of CNT (i.e., MWCNT). Kabir et al. used natural yellow dye sensitizer extracted from the turmeric (*Curcuma longa*). They have fabricated DSSC with natural yellow dye as a sensitizing source for TiO2 photoanode with different MWCNT concentrations. The concentration of MWCNT ranges from 0.005 wt. % to 0.050 wt. %. **Figure 14** shows surface morphology of (a) bare TiO2, (b) MWCNTs, (c) MWCNTs/TiO2,

image of the bare TiO2 and MWCNT (0.25 wt.%)/TiO2 film [44].

photoconversion efficiency (9.0%) [44].

*photoanode based DSSC with N719 dye [35].*

*DOI: http://dx.doi.org/10.5772/intechopen.96630*

**Figure 12.**

**395**

and (d) TiCl4 treated MWCNTs/TiO2 film [45].

#### **Table 1.**

*Different CNT/TiO2 photoanode based DSSC [35].*

Zhang et al. used N719 dye on the CNT photoanode-based DSSC. They prepared two different types of CNT based photoanode: pristine, chemically modified, and O2 plasma-treated CNT. For chemically modified CNT, 500 mg CNT was mixed with 100 ml H2SO4/HNO3 solution (1:1) and kept at 140°C for 6 hours. Afterward, the solution was filtered, cleaned with distilled water, and vacuum dried. For O2 plasma-treated CNT, CNT was treated with O2 plasma treated for 40 minutes at 0.26 Torr (at 50 W) [35].

O2 plasma-treated CNTs/TiO2 photoanode based DSSCs has more uniform holes and rough surface, which provides higher dye adsorption and less charge recombination than either TiO2 or chemical modified CNTs/TiO2. The O2 plasma-treated CNTs/TiO2 photoanodebased DSSC showed 6.34% cell efficiency, which is 75% higher than the conventional TiO2 photoanode based devices (**Table 1**). **Figure 12** illustrates the I-V characteristics of pristine TiO2, chemically modified CNT/ TiO2, and O2 plasma-treated CNT/ TiO2 photoanode based DSSC with N719 dye. The value of the open-circuit voltage of chemically modified CNT/ TiO2 based DSSC was lower than the TiO2 photoanode based DSSC because of poor adhesion between chemically modified CNT/TiO2; however, the overall cell conversion efficiency was 28% higher than the traditional TiO2 based DSSC [35].

Dembele et al. sensitized an ethanolic suspension of MWCNTs (0.006 g of MWCNTs in 15 mL of ethanol) and then mixed with a known weight of TiO2 paste *Improvement of Efficiency of Dye Sensitized Solar Cells by Incorporating Carbon Nanotubes DOI: http://dx.doi.org/10.5772/intechopen.96630*

**Figure 12.**

*I-V characteristics of pristine TiO2, chemically modified CNT/ TiO2 and O2 plasma treated CNT/TiO2 photoanode based DSSC with N719 dye [35].*

to obtain a fixed percentage of MWCNT/TiO2 composite. The MWCNT/TiO2 composites were tape cast on FTO glass substrate. The concentration of MWCNTs was varied in the range of 0–0.250 wt. %. The fabricated photoanodes were soaked in a 0.5 mM ethanolic solution of N719 sensitizer. They were increasing the percentages of MWCNTs in the MWCNT/TiO2 composite, which results in a slight improvement in dye loading (from 0.010–0.020%). In comparison, the average number of dye mole per volume unit improved almost 3.5 times for the 0.25 wt.% MWCNT/ TiO2film than the pure TiO2film. However, this chemisorption of dye multilayers are detrimental for overall cell efficiency: for optimum cell efficiency, the dye should be chemisorbed in a closely packed monolayer. **Figure 13** illustrates the SEM image of the bare TiO2 and MWCNT (0.25 wt.%)/TiO2 film [44].

From **Table 2**, optimized concentration (0.010–0.020 wt.%) of MWCNTs based TiO2 photoanode significantly increases the overall cell conversion efficiency. Introducing a reflection layer into the cell increases the electron lifetime and decreases recombination, leading to improved overall cell performance and photoconversion efficiency (9.0%) [44].

Not only DSSC sensitized with metallic dye, but also DSSC sensitized with natural dye shows similar characteristics to the concentration of CNT (i.e., MWCNT). Kabir et al. used natural yellow dye sensitizer extracted from the turmeric (*Curcuma longa*). They have fabricated DSSC with natural yellow dye as a sensitizing source for TiO2 photoanode with different MWCNT concentrations. The concentration of MWCNT ranges from 0.005 wt. % to 0.050 wt. %. **Figure 14** shows surface morphology of (a) bare TiO2, (b) MWCNTs, (c) MWCNTs/TiO2, and (d) TiCl4 treated MWCNTs/TiO2 film [45].

The integration of MWCNTs improved the cell efficiency of the DSSC by developing a special charge carrier transport channel that is distributed uniformly throughout the TiO2 semiconductor. Cell efficiency of all concentrations of MWCNT incorporated by TiO2 is higher than that of the without MWCNT incorporated by TiO2. The concentration of the MWCNT from 0.000 wt. % to 0.015 wt. %, cell efficiency has improved dramatically (From **Table 3**). The optimum concentration is 0.015 wt. % MWCNTs have a maximum cell efficiency of 1.653%, whereas for without MWCNT integrated TiO2, cell efficiency is 0.921%. After achieving the best possible combination, further increasing the concentration of MWCNT leads to a negative effect on cell parameters such as Isc, Voc, and FF.

Zhang et al. used N719 dye on the CNT photoanode-based DSSC. They prepared two different types of CNT based photoanode: pristine, chemically modified, and O2 plasma-treated CNT. For chemically modified CNT, 500 mg CNT was mixed with 100 ml H2SO4/HNO3 solution (1:1) and kept at 140°C for 6 hours. Afterward, the solution was filtered, cleaned with distilled water, and vacuum dried. For O2 plasma-treated CNT, CNT was treated with O2 plasma treated for 40 minutes at

O2 plasma-treated CNTs/TiO2 photoanode based DSSCs has more uniform holes and rough surface, which provides higher dye adsorption and less charge recombination than either TiO2 or chemical modified CNTs/TiO2. The O2 plasma-treated CNTs/TiO2 photoanodebased DSSC showed 6.34% cell efficiency, which is 75% higher than the conventional TiO2 photoanode based devices (**Table 1**). **Figure 12** illustrates the I-V characteristics of pristine TiO2, chemically modified CNT/ TiO2, and O2 plasma-treated CNT/ TiO2 photoanode based DSSC with N719 dye. The value of the open-circuit voltage of chemically modified CNT/ TiO2 based DSSC was lower than the TiO2 photoanode based DSSC because of poor adhesion between chemically modified CNT/TiO2; however, the overall cell conversion efficiency was

Dembele et al. sensitized an ethanolic suspension of MWCNTs (0.006 g of MWCNTs in 15 mL of ethanol) and then mixed with a known weight of TiO2 paste

0.26 Torr (at 50 W) [35].

**Figure 11.**

**Table 1.**

**394**

*SEM of the cross-section CNT based counter electrode [43].*

*Solar Cells - Theory, Materials and Recent Advances*

**(mA/cm<sup>2</sup> )**

PristineTiO2 6.48 0.84 0.65 3.63

**Voc (V)** **Fill factor (FF)**

8.56 0.83 0.66 4.66 28

11.04 0.85 0.68 6.34 75

**Efficiency (%η)**

**Improvement (%)**

**Photoanode Jsc**

*Different CNT/TiO2 photoanode based DSSC [35].*

Chemically modified CNT/TiO2

O2 plasma treated CNT/TiO2

28% higher than the traditional TiO2 based DSSC [35].

**Figure 15** shows the FESEM image of MWCNT and MWCNT-PMMA composite, and **Figure 16** illustrates the TEM and HR-TEM images MWCNT and MWCNT-

0 500 15.9 7.0 69.0 755 13.6

0.010 500 16.4 9.0 74.0 758 16.0

*Effect of CNT (MWCNT) concentration in the cell performance of N719 bye based DSSC [44].*

**4.3 Effect of CNT based counter electrode on the cell performance of DSSC**

its excellent electrochemical activity. However, using Pt as a counter electrode increases overall cell cost. Many efforts have been made for large surface area and fast electron transportation to apply CNTs to the cathode. CNTs prices are lower than Pt, but it has high electrochemical activity, which makes DSSCs commercially viable. Prasetio et al. sensitized CNT-based cathode by doctor blade method and observed CNT concentration's effect by varying the weight of CNT (0.01, 0.02, and 0.04 g). A slurry was prepared by mixing a fixed mass of (0.01 or 0.02 or 0.04 g) CNT, 0.2 g ethylcellulose, 2 ml ethanol, and 0.8 g terpineol. The slurry was doctor bladed on FTO substrate and dried in the air, followed by annealing at 450°C for 60 minutes. **Figure 17** illustrates SEM images of prepared CNT cathode fabricated with different CNT masses (0.01, 0.02, and 0.04 g) [43].[Use the similar format for

To achieve high cell performance in a large application area, platinum is used for

**Table 7** lists the photovoltaic performance of DSSC fabricated with different masses of CNT as a cathode. Increasing the mass of CNT in the cathode increases the photogenerated current; however, CNT does not increase other cell parameters, such as open-circuit voltage and fill factor. An increase in short circuit current

Ramasamy et al. spray-coated MWCNT on FTO and used it as a cathode. Dispersed MWCNT was sprayed onto FTO glass substrate with a spray gun, which was

**Table 6** lists the photovoltaic performance of DSSC fabricated with MWCNT-PMMA composite. Lee et al. Lee et al. achieved higher cell efficiency of 2.9% (than the reference cell's efficiency of 1.9%), which was possible because of enhanced

PMMA composite [47].

Transparent layer + reflecting layers

Transparent layer + reflecting layers

**Table 2.**

**397**

**Anode structure CNTs**

**(wt %)**

*DOI: http://dx.doi.org/10.5772/intechopen.96630*

**Tannealing (°C)**

**Thickness (μm)**

Transparent layer 0.003 450 12.5 5.6 68.0 700 11.9 Transparent layer 0.007 450 11.5 6.4 67.1 695 13.8

Transparent layer 0 450 12.6 6.5 71.0 745 12.7 1.05

*Improvement of Efficiency of Dye Sensitized Solar Cells by Incorporating Carbon Nanotubes*

Transparent layer 0.010 450 12.8 8.1 71.0 724 15.6 1.05 Transparent layer 0.015 450 9.9 7.9 71.0 734 15.3 1.65 Transparent layer 0.020 450 11.3 7.4 71.0 704 14.8 1.25 Transparent layer 0.045 450 8.8 6.7 71.0 698 13.6 1.35 Transparent layer 0.075 450 10.1 5.9 73.0 707 11.6 1.35 Transparent layer 0.250 450 16.4 1.1 62.0 789 2.2 3.70

**PCE (%)**

**FF (%)**

**Voc (mV)**

**Jsc (mA cm<sup>2</sup> )**

**Dye loading (mol mm<sup>3</sup> <sup>10</sup><sup>7</sup>**

**)**

amorphous structure and ionic conductivity [47].

gram, either g or gr or gram throughout the chapter].

resulted in higher cell conversion efficiency.

Higher concentrations of MWCNTs result in a loss of transparency and low absorption of light, which decreases the photogenerated current [45].

## **4.2 Effect of CNT based electrolyte on the cell performance of DSSC**

As mention earlier (Section 3.2.), CNT based electrolyte not only enhance cell performance of DSSC but also provide improvement in cell structure. Ahmad et al. sensitized a new type of quasi-solid-state electrolyte by dispersing graphene and CNT into the 1-methyl 3-propyl imidazolium iodide (PMII) ionic liquid. They also varied the CNT (i.e., SWCNT) content from 1 wt.% to 16 wt.% in the PMII ionic liquid. Maximum cell efficiency of 1.43% was observed for 7% SWCNT +93% PMII ionic liquid electrolyte (**Table 4**). They have also combined graphene with SWCNT and observed the effect of SWCNT in the quasi-solid-state electrolyte in DSSC application. Combining SWCNTand graphene with PMII enhances cell performance significantly, which is higher than both SWCNT + PMII combination and PMII (**Table 5**) [46].

Lee et al. sensitized MWCNT–polymethyl methacrylate (PMMA) composite electrolyte by thermal polymerization for solid state DSSC. The MWCNT-PMMA composite has made a homogenous solution of 0.26 g MWCNT, 5 g of methyl methacrylate (MMA), and 2-hydroxy-2-methyl-propylphenone (initiator). The solution was vacuum dried and cleaned thoroughly (with dichloroethane (DCE) to remove initiator residue). The MWCNT-PMMA composite was mixed with iodide couples (0.1 M of LiI, 0.015 M of I2, and 0.2 M of t-butyl pyridine) in acetonitrile solvent and stirred for 20 hours for MWCNT-PMMA composite electrolyte.

*Improvement of Efficiency of Dye Sensitized Solar Cells by Incorporating Carbon Nanotubes DOI: http://dx.doi.org/10.5772/intechopen.96630*


#### **Table 2.**

Higher concentrations of MWCNTs result in a loss of transparency and low absorption of light, which decreases the photogenerated current [45].

*SEM images of (a, b, d, e, f) the 0.25 wt.% CNT photoanode at various magnifications, and (c) bare TiO2*

**4.2 Effect of CNT based electrolyte on the cell performance of DSSC**

PMII (**Table 5**) [46].

**396**

**Figure 13.**

*photoanode [44].*

*Solar Cells - Theory, Materials and Recent Advances*

As mention earlier (Section 3.2.), CNT based electrolyte not only enhance cell performance of DSSC but also provide improvement in cell structure. Ahmad et al. sensitized a new type of quasi-solid-state electrolyte by dispersing graphene and CNT into the 1-methyl 3-propyl imidazolium iodide (PMII) ionic liquid. They also varied the CNT (i.e., SWCNT) content from 1 wt.% to 16 wt.% in the PMII ionic liquid. Maximum cell efficiency of 1.43% was observed for 7% SWCNT +93% PMII ionic liquid electrolyte (**Table 4**). They have also combined graphene with SWCNT and observed the effect of SWCNT in the quasi-solid-state electrolyte in DSSC application. Combining SWCNTand graphene with PMII enhances cell performance significantly, which is higher than both SWCNT + PMII combination and

Lee et al. sensitized MWCNT–polymethyl methacrylate (PMMA) composite electrolyte by thermal polymerization for solid state DSSC. The MWCNT-PMMA composite has made a homogenous solution of 0.26 g MWCNT, 5 g of methyl methacrylate (MMA), and 2-hydroxy-2-methyl-propylphenone (initiator). The solution was vacuum dried and cleaned thoroughly (with dichloroethane (DCE) to remove initiator residue). The MWCNT-PMMA composite was mixed with iodide couples (0.1 M of LiI, 0.015 M of I2, and 0.2 M of t-butyl pyridine) in acetonitrile solvent and stirred for 20 hours for MWCNT-PMMA composite electrolyte.

*Effect of CNT (MWCNT) concentration in the cell performance of N719 bye based DSSC [44].*

**Figure 15** shows the FESEM image of MWCNT and MWCNT-PMMA composite, and **Figure 16** illustrates the TEM and HR-TEM images MWCNT and MWCNT-PMMA composite [47].

**Table 6** lists the photovoltaic performance of DSSC fabricated with MWCNT-PMMA composite. Lee et al. Lee et al. achieved higher cell efficiency of 2.9% (than the reference cell's efficiency of 1.9%), which was possible because of enhanced amorphous structure and ionic conductivity [47].

## **4.3 Effect of CNT based counter electrode on the cell performance of DSSC**

To achieve high cell performance in a large application area, platinum is used for its excellent electrochemical activity. However, using Pt as a counter electrode increases overall cell cost. Many efforts have been made for large surface area and fast electron transportation to apply CNTs to the cathode. CNTs prices are lower than Pt, but it has high electrochemical activity, which makes DSSCs commercially viable. Prasetio et al. sensitized CNT-based cathode by doctor blade method and observed CNT concentration's effect by varying the weight of CNT (0.01, 0.02, and 0.04 g). A slurry was prepared by mixing a fixed mass of (0.01 or 0.02 or 0.04 g) CNT, 0.2 g ethylcellulose, 2 ml ethanol, and 0.8 g terpineol. The slurry was doctor bladed on FTO substrate and dried in the air, followed by annealing at 450°C for 60 minutes. **Figure 17** illustrates SEM images of prepared CNT cathode fabricated with different CNT masses (0.01, 0.02, and 0.04 g) [43].[Use the similar format for gram, either g or gr or gram throughout the chapter].

**Table 7** lists the photovoltaic performance of DSSC fabricated with different masses of CNT as a cathode. Increasing the mass of CNT in the cathode increases the photogenerated current; however, CNT does not increase other cell parameters, such as open-circuit voltage and fill factor. An increase in short circuit current resulted in higher cell conversion efficiency.

Ramasamy et al. spray-coated MWCNT on FTO and used it as a cathode. Dispersed MWCNT was sprayed onto FTO glass substrate with a spray gun, which was

#### **Figure 14.**

*SEM image of (a) bare TiO2, (b) MWCNTs, (c) MWCNTs/TiO2, and (d) TiCl4 treated MWCNTs/TiO2 film [45].*


#### **Table 3.**

*I-V performance of different concentrations of the MWCNT incorporated TiO2 based DSSC fabricated with natural yellow dye [45].*


connected to an air compressor. Ramasamy et al. varied the spray time and observed the effect of spraying time on the cell performance of DSSC. Since the spray time is directly related to the thickness of the MWCNT layer, in other words, they have observed the effect of MWCNT coating thickness on the cell performance

*TEM and HR-TEM images of (a, c) MWCNT and (b, d) MWCNT–PMMA composites [47].*

**Content (wt%) Jsc (mA/cm2**

*DOI: http://dx.doi.org/10.5772/intechopen.96630*

**Table 5.**

**Figure 15.**

*graphene in PMII [46].*

100% PMII 0.370 0.575 0.64 0.16 0.01 85% PMII +3% SWCNT +12% graphene 7.32 0.594 0.44 2.50 0.10 85% PMII +12% SWCNT +3% graphene 4.66 0.561 0.43 1.39 0.10

*Improvement of Efficiency of Dye Sensitized Solar Cells by Incorporating Carbon Nanotubes*

*I-V performance of DSSCs with quasi-solid-state electrolytes containing different wt.% of SWCNT and*

*SEM images of (a) MWCNT, and (b and c) MWCNT–PMMA composite film [47].*

**) Voc (V) FF Efficiency (%)**

of DSSC [41].

**399**

**Figure 16.**

#### **Table 4.**

*I-V performance of DSSCs with quasi-solid-state electrolytes containing different wt.% of SWCNTs in PMII [46].*

*Improvement of Efficiency of Dye Sensitized Solar Cells by Incorporating Carbon Nanotubes DOI: http://dx.doi.org/10.5772/intechopen.96630*


**Table 5.**

*I-V performance of DSSCs with quasi-solid-state electrolytes containing different wt.% of SWCNT and graphene in PMII [46].*

**Figure 15.**

**Figure 14.**

*film [45].*

**Table 3.**

**Table 4.**

*PMII [46].*

**398**

*natural yellow dye [45].*

**SWCNT content (wt%) Jsc (mA/cm2**

*Solar Cells - Theory, Materials and Recent Advances*

**MWCNT concentration**

*SEM image of (a) bare TiO2, (b) MWCNTs, (c) MWCNTs/TiO2, and (d) TiCl4 treated MWCNTs/TiO2*

0 wt.% 0.515 0.010 3.792 0.024 0.472 0.007 0.921 0.037 1.13 0.005 wt.% 0.512 0.008 4.973 0.017 0.535 0.003 1.362 0.038 1.15 0.010 wt.% 0.513 0.001 5.346 0.011 0.564 0.001 1.546 0.008 1.22 0.015 wt.% 0.502 0.006 5.995 0.028 0.553 0.009 1.653 0.054 1.37 0.020 wt.% 0.499 0.005 5.119 0.023 0.549 0.010 1.404 0.046 1.34 0.025 wt.% 0.498 0.001 4.873 0.020 0.522 0.002 1.267 0.017 1.31 0.030 wt.% 0.489 0.004 4.543 0.018 0.504 0.006 1.119 0.027 1.28 0.040 wt.% 0.486 0.011 4.543 0.023 0.499 0.008 1.080 0.047 1.28 0.050 wt.% 0.481 0.013 4.361 0.028 0.494 0.003 1.036 0.041 1.25

*I-V performance of different concentrations of the MWCNT incorporated TiO2 based DSSC fabricated with*

0% (only PMII) 0.370 0.575 0.64 0.16 0.01 1% 0.524 0.573 0.70 0.25 0.01 7% 5.19 0.540 0.41 1.43 0.13 10% 2.15 0.616 0.36 0.56 0.02 13% 1.64 0.614 0.41 0.46 0.02 16% 2.09 0.541 0.32 0.40 0.02

*I-V performance of DSSCs with quasi-solid-state electrolytes containing different wt.% of SWCNTs in*

**) Voc (V) FF Efficiency (%)**

**VOC (V) Isc (mA) FF η% Dye loading**

**(mol mm<sup>3</sup> <sup>10</sup><sup>7</sup>**

**)**

*SEM images of (a) MWCNT, and (b and c) MWCNT–PMMA composite film [47].*

**Figure 16.** *TEM and HR-TEM images of (a, c) MWCNT and (b, d) MWCNT–PMMA composites [47].*

connected to an air compressor. Ramasamy et al. varied the spray time and observed the effect of spraying time on the cell performance of DSSC. Since the spray time is directly related to the thickness of the MWCNT layer, in other words, they have observed the effect of MWCNT coating thickness on the cell performance of DSSC [41].


#### **Table 6.**

*I-V performance of DSSC fabricated with MWCNT-PMMA composite [47].*

#### **Figure 17.**

*SEM images of prepared CNT cathode fabricated with different masses of the CNT (a, b) 0.01 gram (c, d) 0.02 gram, and (e, f) 0.04 gram [43].*


MWCNT cathode based DSSC showed higher cell performance (10.04%) due to aligned MWCNT and improved charge carrier conduction path (**Table 9**) [40]. Xiao et al. used Pt/SWCNT film to spray onto the ITO coated polyethylene naphthalate substrate using a vacuum thermal decomposition method at 120°C. The fabricated cathode showed higher light transmittance, higher chemical stability, higher electrocatalytic activity for redox electrolyte, and lower charge carrier transfer resistance [48]. **Table 10** lists the photovoltaic properties of DSSC

*I-V performance of DSSC fabricated with different H2PtCl6.6H2O and SWCNT content [48].*

DSSCs have attracted considerable attention due to their simple fabrication process, inexpensive raw materials, and employment of eco-friendly materials. Recently, to take advantage of their lower electrical resistance, excellent electrocatalytic operation, mechanical integrity, low cost, and flexibility, CNTs

fabricated with different H2PtCl6.6H2O and SWCNT content [48].

**5. Prospects of CNT in DSSC application**

**Spraying time (s) Voc (V) Jsc (mA/cm<sup>2</sup>**

*DOI: http://dx.doi.org/10.5772/intechopen.96630*

*I-V performance of DSSC fabricated with MWCNT based cathode [41].*

**Cathode Jsc (mA/cm<sup>2</sup>**

**SWCNT (%)**

**Table 8.**

**Table 9.**

**Table 10.**

**401**

*MWCNT) [40].*

**H2PtCl6.6H2O (%)**

Bare FTO 0.428 1.48 0.07 0.04 0.772 8.03 0.11 0.68 0.784 12.81 0.15 1.51 0.773 15.67 0.28 3.39 0.778 15.92 0.47 5.82 0.778 15.86 0.57 7.03 0.783 15.64 0.62 7.59

*Improvement of Efficiency of Dye Sensitized Solar Cells by Incorporating Carbon Nanotubes*

Reference Pt coated cathode 17.68 746.27 0.65 8.80 Paste printed MWCNT cathode 15.27 738.43 0.69 8.03 CVD grown MWCNT cathode 17.62 755.89 0.73 10.04

*I-V performance of DSSC with different MWCNT based cathode (different deposition method for*

**Light transmittance (%)**

0.24 0 87 7.29 0.74 0.56 3.00 0.48 0 83 9.42 0.74 0.68 4.71 0.72 0 72 5.86 0.75 0.67 2.91 0.48 0.03 81 9.61 0.75 0.68 4.88 0.48 0.06 80 11.20 0.75 0.71 5.96 0.48 0.012 74 8.53 0.75 0.68 4.33

**Jsc (mA/cm<sup>2</sup> )**

**) FF (%) Efficiency (%)**

**) Voc (V) FF (%) Efficiency (%)**

**Voc (V)**

**FF (%)** **Efficiency (%)**

#### **Table 7.**

*I-V performance of DSSC fabricated with different mass of CNT as cathode [43]*.

**Table 8** lists the I-V parameters of various spraying times of the MWCNT counter electrode. The value of open-circuit voltage is more or less independent of the spray time; however, both short circuit current and fill factor showed a strong dependence on the spraying time of MWCNTs. The charge transfer resistance of the MWCNT cathode in the iodide/tri-iodide electrolyte solution was decreased by increasing the spraying time, which results in a significant improvement in the cell performance of the MWCNT counter electrode based DSSC [41].

Nam et al. used two different methods for CNT counter electrode-based DSSC: screen printing and chemical vapor deposition. Screen printed MWCNT cathode based DSSC showed lower cell performance (8.03%) than the reference Pt cathode based DSSC's cell performance (8.80%) because of unfavorable contact resistance between the MWCNT and FTO. On the contrary, chemical vapor deposited

*Improvement of Efficiency of Dye Sensitized Solar Cells by Incorporating Carbon Nanotubes DOI: http://dx.doi.org/10.5772/intechopen.96630*


#### **Table 8.**

*I-V performance of DSSC fabricated with MWCNT based cathode [41].*


#### **Table 9.**

*I-V performance of DSSC with different MWCNT based cathode (different deposition method for MWCNT) [40].*


#### **Table 10.**

**Table 8** lists the I-V parameters of various spraying times of the MWCNT counter electrode. The value of open-circuit voltage is more or less independent of the spray time; however, both short circuit current and fill factor showed a strong dependence on the spraying time of MWCNTs. The charge transfer resistance of the MWCNT cathode in the iodide/tri-iodide electrolyte solution was decreased by increasing the spraying time, which results in a significant improvement in the cell

*SEM images of prepared CNT cathode fabricated with different masses of the CNT (a, b) 0.01 gram (c, d)*

0.01 2.093 0.49 31 0.32 0.02 4.829 0.48 32 0.74 0.04 6.413 0.45 32 0.91

**Jsc (mA/cm2**

Nam et al. used two different methods for CNT counter electrode-based DSSC: screen printing and chemical vapor deposition. Screen printed MWCNT cathode based DSSC showed lower cell performance (8.03%) than the reference Pt cathode based DSSC's cell performance (8.80%) because of unfavorable contact resistance between the MWCNT and FTO. On the contrary, chemical vapor deposited

performance of the MWCNT counter electrode based DSSC [41].

*I-V performance of DSSC fabricated with different mass of CNT as cathode [43]*.

**Sample Differential scanning calorimetry**

*Solar Cells - Theory, Materials and Recent Advances*

**Melting temperature Tm (°C)**

MWCNT-PMMA

**Table 6.**

**Figure 17.**

**Table 7.**

**400**

**(in gram)**

*0.02 gram, and (e, f) 0.04 gram [43].*

**Mass of CNT in cathode**

**(DSC) data**

*I-V performance of DSSC fabricated with MWCNT-PMMA composite [47].*

**Heat of melting ΔH (J/g)**

PEO 74.3 119..5 1.2 5.7 0.61 53.4 1.9

**Conductivity (mS/cm)**

81.2 97.8 2.3 8.9 0.57 61.8 2.9

**Photovoltaic performance**

**FF (%)** **Efficiency (%)**

**Voc (V)**

**Jsc (mA/ cm2 )**

**) Voc (V) FF (%) Efficiency (%)**

*I-V performance of DSSC fabricated with different H2PtCl6.6H2O and SWCNT content [48].*

MWCNT cathode based DSSC showed higher cell performance (10.04%) due to aligned MWCNT and improved charge carrier conduction path (**Table 9**) [40].

Xiao et al. used Pt/SWCNT film to spray onto the ITO coated polyethylene naphthalate substrate using a vacuum thermal decomposition method at 120°C. The fabricated cathode showed higher light transmittance, higher chemical stability, higher electrocatalytic activity for redox electrolyte, and lower charge carrier transfer resistance [48]. **Table 10** lists the photovoltaic properties of DSSC fabricated with different H2PtCl6.6H2O and SWCNT content [48].
