Strategies for the Implementation of Chenodeoxycholic Acid in Natural Polymer-Based Hydrogels for Stable and Low-Light Effective Quasi-Solid Electrolytes for Aqueous Dye-Sensitized Solar Cells

The disclosing of the full potential of aqueous Dye-Sensitized Solar Cells (a-DSSCs) is tightly bonded to the implementation of more sustainable, stable, and efficient electrolytes which are able to perform both in outdoor and indoor environments. In this contribution, we report the formulation of biopolymer-based hydrogels (e.g., chitosan, carrageenan, and porcine gelatin) in conjunction with ZnO nanoparticles and their application as electrolytes in quasi-solid-state a-DSSC. The thorough characterization (XRD, IR, SEM) of the hydrogels reveals tunable morphology impacting their ability to stabilize a I-based redox mediator and chenodeoxycholic acid (CDCA) employed as an additive. Once implemented in a-DSSCs, all the biopolymer-based quasi-solid electrolytes perform well, delivering a photoconversion efficiency (PCE) approaching or even overcoming 1% (comparable to the one of a reference cell based on xanthan gum), showing an extremely high open circuit voltage (>700 mV). The addition of CDCA, alternatively during the gel formulation or washing phase, enables the porcine gelatin-derived systems to increase their efficiency of about 50% and carrageenan ones to ensure an extremely promising shelf life with any PCE decrease over more than 15 days. More importantly, the porcine gelatin-derived, CDCA-additivated electrolytes are able to properly perform also under indoor light (i.e., 1200 lx), showing PCE values approaching 3% and outperforming reference devices. Our results prove how a thoughtful selection of the polymer scaffold and a specifically designed preparation strategy are fundamental to improve the efficiency of sustainable quasi-solid aqueous electrolytes.