Preparation and characterization of zinc oxide based photoanodes for aqueous dye-sensitized solar cells

This work focuses on the preparation and characterization of zinc oxide photoanodes conceived for water-based dye-sensitized solar cells (DSSCs). Nowadays, one of the main challenges is to replace the commonly used organic electrolyte solvents, which are highly volatile, hazardous and sensitive to moisture/water contaminations with water, the universal, greenest and cheapest solvent. In this work, the redox couples were dissolved only in water and a biosourced jellifying agent, namely carboxymethylcellulose, was added to the electrolyte system to improve the long-term stability of the devices. In the framework of photoanode development, three different microstructures of ZnO with peculiar morphological characteristics were exploited to tailor the photoanode architecture, especially in terms of surface area of the semiconducting layer and electron transfer rate. This target was reached with the desert rose morphology of ZnO. At the same time, the optimization of the sensitization conditions was carried out by means of a chemometric approach in order to limit/overcome the typical ZnO dissolution. Through this method the optimal manufacturing conditions were identified in 1 h of sensitization time and in a molar ratio of 1:50 between dye and co-adsorbent (chenodeoxycholic acid) concentrations in the sensitization solution; this led to an efficiency of 0.34% for lab-scale DSSCs.