# Sustainable Organic Dyes from Winemaking Lees for Photoelectrochemical Dye-Sensitized Solar Cells
)1 Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, Via Torino 155, 30172 Mestre Venice, Italy; [EMAIL_ADDRESS] (A.T.)1 Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, Via Torino 155, 30172 Mestre Venice, Italy; [EMAIL_ADDRESS] (A.T.)1 Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, Via Torino 155, 30172 Mestre Venice, Italy; [EMAIL_ADDRESS] (E.C. )1 Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, Via Torino 155, 30172 Mestre Venice, Italy; [EMAIL_ADDRESS] (E.C. )1 Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, Via Torino 155, 30172 Mestre Venice, Italy; aldair@unive. energy to electrical energy. Organometallic dyes, which are based on ruthenium (Figure 1a) and osmium polypyrid complexes, have been widely employed as efficient sensitizers [3; 4], since they can absorb light in the visible range, have intense charge-transfer and highly efficient metal-ligand charge transfer. Unfortunately, this kind of metal coordination compounds is usually obtained with multistep reactions and expensive chromatographic purification procedures [1]. The use of organic dyes is an alternative to transition metals, leading to a significant reduction of manufacturing costs of the final device [5; 6; 7]. Many organic dyes are available in nature and they can be used as such. In fact, plants are full of natural pigments that determine their colour, covering the entire solar spectrum from red to purple and that can be employed in DSSCs. Therefore, natural dye molecules can be used like a sensitizer for their low cost, good light absorbance, easily preparation process, and eco-friendly behaviour, as they are completely biodegradable. One of the most important groups of naturally occurring pigments are anthocyanins, which are responsible for red, blue, and purple colours in different plant tissues, like fruits, flower, leaves, and bulbs [8]. These polyphenolic molecules are available in various fruits, such as berries, grapes, pomergranates, raspberries, and many other [9], and, during the impregnation process, can bind the semiconductor titania nanoparticles with their hydroxyl functional group, to obtain an electronic coupling that allows for an efficient electron transfer reaction. Anthocyanins [10; 11] and other several natural dyes, such as tannins [12], carotenoids [13; 14], flavonoids [5; 15], and chlorophylls [16; 17] (Figure 1b,c), can be easily extracted from vegetables or fruits and used to build DSSCs [1; 5] that are characterized by typical efficiency included between 0 and 2%. This difference is depending, among other things, on the starting material that provides different efficiency, such as 0.64% for eggplants, 0.90% for Radicchio, 1.07% for blackberries, and 0.78% for Red Sicilian orange [9]. Nevertheless, an ethical question arises, since food has to be used and destroyed to obtain dyes from fruits and vegetables. Therefore, developing such a technology on a large scale could be considered incorrect from an ethical point of view and, at the end, also economically disadvantageous. It is necessary to recover and exploit the concept of circular economy, which considers the whole product's life-cycle, from its production to the creation of markets for waste-derived raw materials. Waste-to-energy is a broad term that encompasses various waste treatment processes generating energy (e.g. in the form of electricity, heat, or produce a waste-derived fuel), each of which has different environmental impacts and circular economy potential. The innovative idea behind this applied research work, developed in collaboration with a venetian winery, consists of recovering and valorizing the waste of winemaking process, principally lees after fermentation and clarification processes, for the realization of DSSC solar cells.