Quantum Dot–Dye Co-Sensitized Solar Cells Based on TiO₂–rGO Photoanodes Using CdS and Methylene Blue

In this study, TiO2–rGO nanocomposites were synthesized and used as photoanode materials in quantum dot-sensitized solar cells. In the solar cells, CdS quantum dots and methylene blue (MB) dye were used as sensitizers. A comparative study was conducted using MB dye and CdS quantum dots individually and together as co-sensitizers. Thus, the synergistic effect between the MB dye and CdS quantum dots was effectively utilized. The efficiencies of the solar cells with TiO2-rGO nanocomposite photoanodes were higher than those of the solar cells fabricated with pure TiO2 photoanodes. The solar cell based on TiO2–rGO with MB–CdS dual sensitization exhibited the highest efficiency of 0.21%, whereas the efficiencies obtained for TiO2–rGO/CdS, TiO2/CdS, and TiO2/MB–CdS solar cells were 0.20%, 0.08%, and 0.07%, respectively. The synergistic effect between the MB dye and CdS quantum dots enhanced photon absorption, thereby improving the overall efficiency of the cell. These findings demonstrate that dual sensitization combined with TiO2–rGO photoanodes provides an effective strategy for improving light harvesting and charge transport in quantum dot-sensitized solar cells.