# Sustainable Organic Dyes from Winemaking Lees for Photoelectrochemical Dye-Sensitized Solar Cells
## 3 Results and Discussion
### DSSCs Efficiencies  
The photovoltaic performances of DSSCs using natural winemaking lees dyes as the photosensitizer (TiO\({}_{2}\)-dye/electrolyte containing I, I\({}_{3}\)-/Pt counter electrode) were determined to evaluate the cell power and the photocurrent generated in the presence of the solar simulator. The J-V and P-V curves can be used to determine the open circuit voltage (V\({}_{\text{OC}}\)), the short circuit current density (J\({}_{\text{SC}}\)), the fill factor (FF), and the efficiency (\(\eta\)). The same photocurrent tests for the cell using bare TiO\({}_{2}\)-400 electrode determined under identical experimental conditions were also carried out and, as expected, no current was observed. DSSCs was realized with the mesoporous nanostructured titania calcined at 400 \({}^{\circ}\)C and using four different organic dyes that were extracted from winemaking lees to impregnate the semiconductor layer. Figure 10 reports the J-V and P-V curves of these solar cells.  
As reported in Table 3, the efficiency of cells built with white wine lees has lower efficiency than red wine extract, due to the poor content of anthocyanins that limits the absorption of visible light radiation. Using Soxhlet extraction for both red and white winemaking lees can increase the performance of the cell, most probably due to the tannins reaction, which leads to an increase in red-coloured molecules that can absorb in the visible range and efficiently transfer excited electron to semiconductor layer. The best efficiency \(\eta\) was obtained by red wine extract made with Soxhlet, showing a V\({}_{\text{oc}}\) and J\({}_{\text{sc}}\) values of 0.492 V and 1.47 mA/cm\({}^{2}\), respectively. All these data are comparable with the typical values of an organic dye sensitized solar cell [9] built with dyes that were extracted from vegetables and fruits.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Anthocyanins (g L\({}^{-1}\))** & **Tannins (g L\({}^{-1}\))** & **Catechins (g L\({}^{-1}\))** \\ \hline A & 1.84 & 0.32 & 0.10 \\ B & 1.88 & 1.97 & 0.10 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Anthocyanins, tannins, catechins, and total polyphenols characterizations of extracted dye from red wine lees. (A) Soxhlet extraction with 1:3 less-solvent ratio, in ethanol; (B) room temperature (RT) extraction with 1:1 wt lees-solvent ratio, in ethanol. Relative uncertainties are less than 10%.  
Figure 10: J-V curves of the DSSC prototypes realized with red and white winemaking lees extract. R-RT is the extract of red wine lees at RT; R-S extract of red wine lees with Soxhlet; W-RT is the extract of white wine lees at RT; W-S extract of white wine lees with Soxhlet.  
Plant kingdom is full of dyes and, depending on fruit, flower or leaf concentration of photosensitive molecules, can significantly vary. Although winemaking lees are widely available, every kind of grape also has different types of polyphenols and different concentrations. Moreover, differences of polyphenols composition depending on the picking times of the grapes are possible, also employing the same type of processed wine.  
Two kinds of red wine lees can lead to different efficiency, although lees have been subjected to the same extraction process, as reported in Figure 11.  
Efficiency, Jsc and Voc are comparable with other DSSCs existing in literature (Table 4) and built while using grapes or wine as dyes. As expected, changing the typology of grapes and wine leads to a widely different efficiency, from 0.025% to 0.57%. For the future it is desirable to further study the variation of winemaking lees composition during the year to understand how the grapes properties can affect the final composition of winemaking lees and eventually purify the extracts to obtain more comparable solutions during the year since vegetables and fruits are natural agricultural products subjected to climatic conditions.