<![CDATA[Natural-dye-sensitized TiO2 films are promising photoanode materials for dye-sensitized solar cells (DSSCs) because natural dyes provide visible-light absorption and offer an environmentally friendly alternative to synthetic sensitizers. This study investigated the influence of sensitizer type, co-sensitization, and TiO2 crystallite size on the optical absorption properties and apparent optical band gap of dye-sensitized TiO2 films. Micro- and nano-TiO2 films sensitized with Citrus hystrix, Curcuma sp., and mixed-dye sensitizers were deposited on indium tin oxide (ITO) substrates by spin-coating. The optical responses of the films were analyzed using UV-Vis spectroscopy, and the apparent optical band gap energies were determined using the Tauc plot method. The research revealed that both sensitizer type and TiO2 crystallite sizes influenced the optical properties of the samples. Films containing Citrus hystrix exhibited higher optical absorption than those containing Curcuma sp. in both micro- and nano-TiO2 systems. The apparent optical band gap ranged from 2.82 to 3.68 eV. Of all the samples investigated, the nano-TiO2/Citrus hystrix films showed the least apparent optical band gap of 2.82 eV, revealing the most extended optical response toward low photon energies. Although co-sensitization extended the absorption profile, it did not yield lower apparent optical band-gap energies than those of the Citrus hystrix films. These results suggest that the optical behavior of dye-incorporated TiO2 films depends on the sensitizer-TiO2 combination. Each film configuration was fabricated and measured once; therefore, the reported values represent individual measurements without replicate-based statistical uncertainty. The results shed light on the production of TiO2-based photoanodes that are environmentally friendly for DSSC applications.]]>
