Development of DSSC photovoltaic cells for energy production through the recovery of winemaking by-products

Global energy consumption is currently based on fossil fuels but, in recent years, due to the decreasing availability of non-renewable resources and the increasing energy demand, the scientific world has pushed the research on more sustainable resources. Among them, solar energy, free, inexhaustible and clean source, has been much more studied, with the aim of optimizing materials, technologies and processes to obtain green electrical energy. Photovoltaic cells (PVs) are devices able to carry out this conversion and technologies based on the use of organic materials are raising interest, since they could be a viable alternative to the traditional systems based on silicon. The most promising PVs are the so-called Dye Sensitized Solar Cells (DSSCs), which mimic the natural chlorophyll photosynthesis process. One of the most important cells’ elements is the dye, which absorbs sunlight and injects electrons in a semiconductor on which it is adsorbed, generally titania, a non-toxic and low-cost oxide. The organic dyes adsorbed on the semiconductor are usually natural colorants extracted from blueberries, oranges, blackberries, currants, olives, grapes and many other fruits and vegetables [1]. Nevertheless, developing such a technology based on food on a large scale could be considered incorrect from an ethical point of view and, at the end, economically disadvantageous too. 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. The innovative idea behind this applied research work, developed in collaboration with Vinicola Serena srl, a venetian winery located in the Prosecco region, consists in recovering and valorizing, through innovative solutions, the waste of winemaking process called “lees”, for the realization of DSSC solar cells. Generally, at the end of winemaking and clarification wine process, the precipitate on the bottom is composed mostly of bentonite, that slightly bleaches wines, absorbing molecules that, properly extracted, can be valorized and used as dyes in DSSCs. In this work, a nanostructured titania was synthetized by a sol-gel approach and characterized by physisorption at -196 °C, X-ray diffraction, scanning electron microscopy and diffuse reflectance spectroscopy. The synthetized nanoparticles, with an average size < 50 nm, showed an ordered mesoporous network with high surface area (> 100 m2g-1), exhibiting the main diffraction peaks and characteristic band gap of anatase phase. Organic dyes (tannins, anthocyanins, polyphenols, catechins), after extraction with green solvents from winemaking lees and characterization to estimate the concentrations of each dye and the color intensity, were adsorbed on the high surface area TiO2 matrix. DSSC prototypes were then assembled and tested to evaluate the power density and photocurrent generated under simulated solar light irradiation. The results, obtained using dyes extracted from winemaking lees, were comparable with the typical values of a DSSC reported in the literature [1]. This novel approach can represent an eco-friendly and low environmental impact solution to produce electrical energy by transforming an agri-food waste into a resource.