*Effect of Combination of Natural Dyes and the Blocking Layer on the Performance of DSSC DOI: http://dx.doi.org/10.5772/intechopen.94760*

semiconductor material [16]. **Figure 4** shows the basic interaction between anthocyanin and semiconductor material (e.g., TiO2).

Carotenoids occur in many plants and algae, as well as several bacteria, and fungi. It contributes to yellow, orange, and red colors and allows them to absorb short-wave visible light [32]. Carotenoids can be divided into two major types: xanthophylls (with oxygen) and carotenes (purely hydrocarbons and without oxygen) [16, 33]. **Figure 5** illustrates the interaction between carotenoids- semiconductor material (i.e., TiO2).

Flavonoids are essential floral pigments. The development of a specific color depends on the accumulation of flavonoid chromophores and other intrinsic and extrinsic factors. Chemically, the flavonoids have a C6- C3- C6 carbon framework with two connected two phenyl rings (A and B) and a heterocyclic ring (C). Depending on the oxidation potential of the C-ring, the particular flavonoids absorb light in the visible wavelength. Till now, over 5000 flavonoids have been identified from different plants. Most of the flavonoid pigment has loosely or unbound electrons. Thus less energy is required for excitation of such electrons is lower compared to the others. As a result, those pigment molecules can be energized by the light within the visible range [16].

The overall cell efficiency of natural dye-based DSSCs is comparably low compared to DSSCs sensitized with sensitized dyes. Due to the inadequate interaction between dyes and semiconductor surface, a significant reduction of the cell's shortcircuit current. The pigment's long structure obstructs the dye molecules to form a bond with the oxide surface of the semiconductor materials effectively. Those are the field of works that are yet to be developed in natural dye DSSCs to achieve highefficiency devices and device stability. To further raise the efficiency of the DSSC combination of dyes has been explored and reported DSSC or to broaden the absorption spectrum [35–39]. A combination of natural dyes with an optimized choice of the extracting solvent enhances the absorption of solar light and allowed utilization of the photon energy more efficiently. As a result, DSSC sensitized with the dye mixture shows higher absorbance, and cumulative absorption properties over the entire visible region than the DSSC fabricated with single individual dyes [35, 36].

Kabir et al. studied the effect of chlorophyll and anthocyanin dye mixture on the cell performance of natural dye-based DSSC. They also mixed the dyes at five different volume ratios to find the optimized dye mixture. The cell conversion efficiency of DSSC fabricated with individual chlorophyll, and anthocyanin dyes

**Figure 5.** *Carotenoids -semiconductor material (i.e.,TiO2) interaction [34].*

Anthocyanins are also an abundant and widespread group of water-soluble pigments in plants. They absorb light at the longest wavelengths. Depending on the pH value, anthocyanins are responsible for the existence of attractive colors, such as red, orange, magenta, pink, blue, blue-black and purple floral [16, 30]. Generally, the carbonyl and hydroxyl functional groups in the anthocyanin dye sensitizers create an electronic coupling with the semiconductor material's conduction band, which helps transfer the excited electron efficiently to the conduction band of

*Basic structure of anthocyanin and anthocyanin-semiconductor material (TiO2) intaraction [31].*

**Figure 3.**

**Figure 4.**

**318**

*Chlorophyll-semiconductor material (i.e.,TiO2) interaction [29].*

*Solar Cells - Theory, Materials and Recent Advances*

were 0.466% and 0.531%, respectively. DSSC co-sensitized with the optimized dye mixture (20% chlorophyll +80% anthocyanin) showed cell conversion efficiency of 0.847%, which is almost 1.82 and 1.6 times higher than the cell efficiency of the individual chlorophyll and anthocyanin dye-sensitized DSSC's (shown in **Figure 6**). The chemical characteristics study of the dye showed that no new bond except has formed; however, few shifts in the adsorption peak was observed (Shown in **Figure 7** and **Table 1**). Similar characteristics were seen when dyes were adsorbed the TiO2 semiconductor material (shown in **Figure 8**. and **Table 2**, [36].

**Figure 9** illustrates the UV–visible absorption spectra of natural chlorophyll (green), anthocyanin (red), and the optimum combination of dyes (green + red) diluted in ethanol. The dye mixture has demonstrated the cumulative absorption properties of both individual green and red dye.

Kabir et al. also studied the effect of betalain and curcumin dye combination on the cell performance of natural dye-based DSSC. They also mixed the dyes at three different volume ratios to find the optimized dye combination. The optimized dye mixture demonstrated the cumulative absorption properties of both individual betalain and curcumin dye (shown in **Figure 10**). The DSSC fabricate with the combination of betalain and curcumin dye also showed superior cell performance than DSSC manufactured with individual betalain and curcumin dye (shown in **Figure 11** and **Table 3**) [35].

#### **Figure 6.**

*I-V characteristics of DSSC fabricated with chlorophyll, anthocyanin and different combinations [36].*

Nonetheless, to the best of our knowledge, combination of dyes have a positive

*FT-IR adsorption spectra of natural chlorophyll (green), anthocyanin (red), and combination*

In DSSCs, a porous layer of nanostructuredsemiconductor materials such as TiO2 [40–45], ZnO [46–48], SnO2 [49, 50], SrTiO3 [51, 52] Zn2SnO4 [53, 54] and Nb2O5 [55] called a photo anode, covered with photosynthetic dye. The photo anode of

impact on the cell performance of natural based DSSC.

**4. Effect of blocking layer in DSSC**

*(20% green +80% red) of dyes (with TiO2) [36].*

**Functional group**

Alkyl Halide (CdCl)

Alkene (═CdH)

Aromatic (C═C)

Alcohol (OdH)

*red) without TiO2 [36].*

**Table 1.**

**Figure 8.**

**321**

**Absorption range (in cm<sup>1</sup> )**

*DOI: http://dx.doi.org/10.5772/intechopen.94760*

Alkane (CdH) 2820–2850 Stretch

Alkane (CdH) 2850–3000 Stretch

**Type of vibration**

1400–1600 Stretch Medium

(symmetric)

(asymmetric)

3200–3600 Stretch Broad

**Intensity Absorption**

600–800 Stretch Strong 616 610 606

675–1000 Bending Strong 944 950 —

Ether (CdO) 1000–1300 Stretch Strong 1017 1026 — Amine (CdN) 1080–1360 Stretch Weak 1338 1354 —

*Effect of Combination of Natural Dyes and the Blocking Layer on the Performance of DSSC*

Alkene (C═C) 1620–1680 Stretch Variable 1652 1619 1635

weak

and strong

*IR absorption of organic functional groups of natural green, red, and combination of dyes (20% green +80%*

**peak of green dye (in cm<sup>1</sup> )**

**Absorption peak of combination of dyes (in cm<sup>1</sup> )**

1422 1404 —

3346 3320 3329

Strong 2837 — —

Strong 2975 — —

**Absorption peak of red dye (in cm<sup>1</sup> )**

#### **Figure 7.**

*FT-IR adsorption spectra of natural chlorophyll (green), anthocyanin (red), and combination (20% green +80% red) of dyes (without TiO2) [36].*


*Effect of Combination of Natural Dyes and the Blocking Layer on the Performance of DSSC DOI: http://dx.doi.org/10.5772/intechopen.94760*

#### **Table 1.**

were 0.466% and 0.531%, respectively. DSSC co-sensitized with the optimized dye mixture (20% chlorophyll +80% anthocyanin) showed cell conversion efficiency of 0.847%, which is almost 1.82 and 1.6 times higher than the cell efficiency of the individual chlorophyll and anthocyanin dye-sensitized DSSC's (shown in **Figure 6**). The chemical characteristics study of the dye showed that no new bond except has formed; however, few shifts in the adsorption peak was observed (Shown in **Figure 7** and **Table 1**). Similar characteristics were seen when dyes were adsorbed

**Figure 9** illustrates the UV–visible absorption spectra of natural chlorophyll (green), anthocyanin (red), and the optimum combination of dyes (green + red) diluted in ethanol. The dye mixture has demonstrated the cumulative absorption

Kabir et al. also studied the effect of betalain and curcumin dye combination on the cell performance of natural dye-based DSSC. They also mixed the dyes at three different volume ratios to find the optimized dye combination. The optimized dye mixture demonstrated the cumulative absorption properties of both individual betalain and curcumin dye (shown in **Figure 10**). The DSSC fabricate with the combination of betalain and curcumin dye also showed superior cell performance than DSSC manufactured with individual betalain and curcumin dye (shown in

*I-V characteristics of DSSC fabricated with chlorophyll, anthocyanin and different combinations [36].*

*FT-IR adsorption spectra of natural chlorophyll (green), anthocyanin (red), and combination (20% green*

the TiO2 semiconductor material (shown in **Figure 8**. and **Table 2**, [36].

properties of both individual green and red dye.

*Solar Cells - Theory, Materials and Recent Advances*

**Figure 11** and **Table 3**) [35].

**Figure 6.**

**Figure 7.**

**320**

*+80% red) of dyes (without TiO2) [36].*

*IR absorption of organic functional groups of natural green, red, and combination of dyes (20% green +80% red) without TiO2 [36].*

**Figure 8.**

*FT-IR adsorption spectra of natural chlorophyll (green), anthocyanin (red), and combination (20% green +80% red) of dyes (with TiO2) [36].*

Nonetheless, to the best of our knowledge, combination of dyes have a positive impact on the cell performance of natural based DSSC.
