Effects of Co-sensitising Chlorophyll and Betanin dyes on Optical Absorption properties and Photovoltaic performance of titanium dioxide-based Dye-S

To address the increasing energy demands, renewable energy technologies, such as Dye-Sensitised Solar Cells (DSSCs), are considered due to their low fabrication costs and environmental friendliness. However, to date, reduced optical absorption and low carrier collection are the primary reasons for the low Power Conversion Efficiency (PCE) of DSSCs. Previous studies have shown that natural dyes are potential sensitisers and co-sensitisers that enhance the performance of these solar cells. The present work focused on the application of natural dyes, betanin (Beta vulgaris) and chlorophyll (Spinacea oleracea), in DSSCs synthesised using titanium dioxide (TiO2) mesoporous films. The pigments were blended in a 1:1 volume ratio. The measurements of optical characteristics were performed using a UV-Vis spectrometer (400-800 nm), while an FT-IR spectrometer was used to determine functional groups. Chlorophyll had a broad absorption peak at 427 and 673 nm, whereas betanin showed a peak at 527 nm. The spectral interactions were confirmed by the shift of chlorophyll peaks to 440 and 671 nm, whereas betanin exhibited a bathochromic shift of 22 nm in the composite dye, respectively. FT-IR analysis revealed the presence of various functional groups, including O-H, C=O, C-H, and C-O, which are essential for light absorption and binding to TiO2. The co-sensitised DSSCs showed enhanced photovoltaic performance compared to the single-dye cells with a current density (JSC) of 1.22 mA/cm2, open-circuit voltage (VOC) of 0.63 V, and PCE of 0.56 %. These results demonstrate that natural dye co-sensitisation can be a practical approach for enhancing light trapping and efficiency in DSSCs, offering a sustainable alternative for solar energy applications