# Overview on Different Types of Solar Cells: An Update
## 4 Dye-Sensitized Solar Cells
### The Development of Natural Dye from Plant Extracts in DSSCs  
Many researchers have developed DSSCs by utilizing various types of natural dyes from plant extracts. Some that have been developed include dye extracts or plant pigments such as chlorophyll extract [162], anthocyanins [163], and beta caroten [164]. One of the results of the DSSC that has been developed [164] by using carotenoids succeeded in making DSSCs with an efficiency of 3% and which were stable after 1 h of sunlight exposure. Beta-carotene is found in every part of the plant, namely from flowers, fruits, stems, and roots, and provides pigments to fruits and flowers with distinctive red, orange, and yellow colors [165]. Plant pigmentation occurs because the structure of the pigment interacts with sunlight to change wavelengths that are either transmitted or reflected by plant tissues [166; 167; 168].  
Carotenoids are involved in photosystems and contribute to energy absorption in the visible light spectrum by transferring the absorbed energy to chlorophyll. Carotenoids also protect from excess light through energy dissipation, the detoxification of free radicals, and limiting damage to cell membranes. In addition, highly conjugated carotenoids can function as short-wire molecules that mediate the electron transfer in donor-acceptor complexes and membranes. Figure 10 shows beta-carotene having a series of delocalizations, but on a larger scale with 11 carbon-carbon double bonds conjugated together [169]. Beta-carotene absorbs the visible light spectrum between 380 and 520 nm. Therefore, it takes less energy to push electrons on beta-carotene than TiO\({}_{2}\), which works in the ultraviolet range (\(<\)400 nm). The number of conjugated double bonds (CDB), maximum absorption (\(\lambda\)max), and carotenoid colors are presented in Table 1.  
\begin{table}
\begin{tabular}{c c} \hline
**Trivial Name** & **Semi-Systematic Name** \\ \hline \(\zeta\)-carotene & 7,8,7,8′-tetrahydro-\(\psi\), \(\psi\)-carotene \\ \hline Neurosporene & 7,8-dihydro-\(\psi\), \(\psi\)-carotene \\ \hline Pro-lycopene & 7Z,9Z,7′Z,9′Z-tetra-cis-\(\psi\), \(\psi\)-carotene \\ \hline Lycopene & \(\psi\), \(\psi\)-carotene \\ \hline \(\gamma\)-carotene & \(\beta\), \(\psi\)-carotene \\ \hline \(\delta\)-carotene & \(\varepsilon\), \(\psi\)-carotene \\ \hline \(\alpha\)-carotene & \(\beta\), \(\varepsilon\)-carotene \\ \hline zeinoxanthin & \(\beta\), \(\varepsilon\)-carotene-3,-ol \\ \hline lutein & \(\beta\), \(\varepsilon\)-carotene-3,3′-diol \\ \hline \(\beta\)-carotene & 7,8-dihydro-\(\beta\), \(\beta\)-carotene \\ \hline \(\beta\)-cryptoxanthin & \(\beta\), \(\beta\)-carotene-3-ol \\ \hline Zexanathin & \(\beta\), \(\beta\)-carotene-3,3′-diol \\ \hline anthexaranthin & 5,6-epoxy-5,6-dihydro-\(\beta\), \(\beta\)-carotene-3,3′-diol \\ \hline \end{tabular}
\end{table}
Table 1: Trivial name and semi-systematic names of carotenoids.  
Figure 10: The structure of beta-carotene [169].  
The trivial and semi-systematic names of carotenoids are shown in Table 1. The number of conjugated double bonds (CDB) was compared with the maximum absorbance spectra (\(\lambda_{\text{max}}\)) and the color of the carotenoid solutions. The maximum absorbance spectra expressed in acetonitrile/ethyl acetate solution were measured using high-performance liquid chromatography (HPLC) with a PDA detector [170] unless otherwise stated. Beta-carotene is one of the most abundant classes of carotenoids found in food and is used as a food coloring. Plants that produce beta-carotene include corn [171], pumpkin, carrots, tomatoes, and melinjo fruit. Schematically the working principle of DSSC is shown in Figure 11. In the simplest arrangement, the DSSC consists of a transparent conductive glass coated with nanocrystalline TiO\({}_{2}\) (nc-TiO\({}_{2}\)), a dye molecule bound to the nc-TiO\({}_{2}\) surface, and an electrolyte such as \(\Gamma\)/I\({}^{3-}\), with illuminated cells capable of generating voltages and currents [172].