Fast and green process to obtain astaxanthin-rich extracts from shrimp shell waste for dye sensitized solar cells

Aiming to address the critical need for renewable energy, this study explores the potential of astaxanthin-rich extracts from shrimp waste as natural sensitizers for dye-sensitized solar cells (DSSCs) using an eco-friendly and economically viable process. Photoconversion efficiencies (PCE) of astaxanthin-based DSSCs were evaluated through I-V measurements while charge transfer resistances (R_CT) were assessed by electrochemical impedance spectroscopy. The sensitizer preparation involved extraction of astaxanthin from waste shrimp (Aristaeomorpha foliacea) cephalothoraxes, which were desiccated, finely milled and treated with ethyl acetate, to obtain a crude extract very rich in astaxanthin mainly present in esterified forms. The extraction process was fast and avoided extreme experimental conditions in terms of energy consumption, ultra-vacuum, high temperatures and use of toxic solvents. Direct application of the crude extract as sensitizer for DSSCs resulted in low PCE (0.09 %) and high R_CT, due to the limited ability of esterified astaxanthin to interact with the TiO₂ layer. This limitation was overcome through saponification of the extract with methanolic NaOH, leading to free astaxanthin with high recovery yield and limited degradation. The saponified extract showed lower R_CT and higher PCE (0.30 %). These results highlight the promising potential of suitably processed shrimp waste as a source of sensitizers for DSSCs.