Evaluation of Calendula officinalis Extract as a Functionalization Agent for Gold Nanoparticles / Comprehensive Multi-Technique Analytical Characterization and its use as a Dye-Sensitized Solar Cell Sensitizer

Calendula officinalis extract was evaluated as a functionalization agent for gold nanoparticles (AuNPs). The resulting nanoconjugate (AuNP-Cale) was thoroughly characterized, and explored as a sensitizer for dye-sensitized solar cells (DSSC). As a starting point, citrate-reduced AuNPs (AuNP-Cit) were synthesized and fully characterized. Comprehensive characterization for both AuNP-Cit and AuNP-Cale included dynamic light scattering (DLS), electrophoretic light scattering (ELS), colloidal and stability assay. Successful functionalization included increased hydrodynamic diameter, reduced zeta potential, and improved colloidal stability. DSSC evaluation demonstrated that while pre-formed AuNP-Cale did not enhance efficiency, improved performance was achieved when AuNP-Cit was added sequentially after the extract on the TiO2 electrode, likely due to better electrode coverage. This result correlated with enhanced light absorption (FORS) and favorable EIS parameters.