Dye-sensitized solar cells have been under development for the last three decades but are yet to see the market. This has been attributed to stability issues of the electrolyte in the cell. Electrolytes can be liquid, quasi-solid, or solid. Liquid electrolytes were the first to be developed and, therefore, have been subject to radical revisions in both composition and applicability. They have shown the best power conversion efficiencies but have poor thermal stability. Although quasi-solid and solid-state electrolytes were developed to overcome these stability issues, they too have their limits. The aim of this paper is to explore the development of liquid electrolytes, outlining the current state of the technology and considering their potential in the photovoltaic market.

In times of climate change and dwindling fossil resources, the need for sustainable renewable energy technologies gains importance, increasingly fast. However, the state of the art technologies are energy intensive in their production, like monocrystalline photovoltaic, or even consist of not recyclable composite material, in the case of wind turbine blades. Despite a lack in efficiency and stability, dye sensitized solar cells (DSSC) have a high potential to supplement the state of the art green energy technology in future. With low production costs and no necessity for toxic compounds DSSCs are a potential product, which could circulate in the loops of a circular economy. Therefore, with this paper, we provide the status of research on DSSC recycling and an outlook on how recycling streams could be realized in the future for glass-based DSSCs without toxic components. The overview includes work on using recycled material to build DSSCs and extending the life of a DSSC, e.g., through rehydration. We also illustrate the state of sustainability research for DSSCs using the VOSviewer tool. To date, the term sustainability appears in 35 of 24,441 publications on DSSCs. In view of the global challenges, sustainability should be researched more seriously because it is as important as the efficiency and stability of DSSCs.

Keratin is one of the most important protein materials and can act as a sustainable biopolymer for manifold applications. This paper reports on a sustainable extraction method for keratin from wool fiber materials. The use of this extracted keratin for polymer film preparation and preparation of nano-composite materials by electrospinning is investigated. The preparation of keratin films is done in combination with the both biopolymers alginate and pectin. Keratin nanofibers are prepared in combination with the polymer polyacrylonitrile PAN. A view on antibacterial properties of the prepared films is given. As further analytic methods, Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetry, and scanning electron microscopy (SEM) are used. Finally, the preparation of new keratin containing materials is described, which may be used in future for biomedical applications.

To overcome the long-term stability problems of dye-sensitized solar cells (DSSC) due to solvent evaporation and leakage, gelling the electrolyte with polymers is an appropriate option. Especially for future applications of textile-based DSSCs, which require cost-effective and environmentally friendly materials, such an improvement of the electrolyte is necessary. Therefore, the temporal progressions of efficiencies and fill factors of non-toxic glass-based DSSCs resulting from different gel electrolytes with poly(ethylene oxide) (PEO) are investigated over 52 days comparatively. Dimethyl sulfoxide (DMSO) proved to be a suitable non-toxic solvent for the proposed gel electrolyte without ionic liquids. A PEO concentration of 17.4 wt% resulted in an optimal compromise with a relatively high efficiency over the entire period. Lower concentrations resulted in higher efficiencies during the first days but in a poorer long-term stability, whereas a higher PEO concentration resulted in an overall lower efficiency. Solvent remaining in the gel electrolyte during application was found advantageous compared to previous solvent evaporation. In contrast to a commercial liquid electrolyte, the long-term stability regarding the efficiency was improved successfully with a similar fill factor and thus equal quality.

The electrolyte for dye-sensitized solar cells (DSSCs) is subject of constant innovation, as the problems of leakage and drying greatly reduce the long-term stability of a device. One possible way to solve these problems is the use of gel polymer electrolytes (GPEs) with a gelling structure, which offer different advantages based on the used polymers. Here, potential GPE systems based on dimethyl sulfoxide (DMSO) as solvent for low-cost, non-toxic and environmentally friendly DSSCs were investigated comparatively. In order to observe a potential improvement in long-term stability, the efficiencies of DSSCs with different GPEs, consisting of polyacrylonitrile (PAN), acrylonitrile-butadiene-styrene (ABS), polyvinyl alcohol (PVA) and poly (vinylidene fluoride) (PVDF) and their blends with poly (ethylene oxide) (PEO), were investigated over a period of 120 days. The results indicate that blending the polymers with PEO achieves better results concerning long-term stability and overall efficiency. Especially the mixtures with PAN and PVDF show only slight signs of deterioration after 120 days of measurement.