Comparative Study of TiO₂, ZnO, and Nb₂O₅ Photoanodes for Nitro-Substituted Naphthoquinone Photosensitizer-Based...

This research focuses on the first demonstration of NO₂Lw (2-hydroxy-3-nitronaphthalene-1,4-dione) as a photosensitizer and TiO₂, ZnO, and Nb₂O₅ as photoanode materials for dye-sensitized solar cells (DSSCs). The metal-free organic photosensitizer (i.e., nitro-group-substituted naphthoquinone, NO₂Lw) was synthesized for this purpose. As a photoanode material, metal oxides, such as TiO₂, ZnO, and Nb₂O₅, were selected. The synthesized NO₂Lw contains an electron-withdrawing group (-NO₂) and anchoring groups (-OH) that exhibit absorption in the visible range. The UV-visible absorbance spectrum of NO₂Lw demonstrates the absorption ascribed to ultraviolet and visible region charge transfer. The NO₂Lw interacts with the TiO₂, ZnO, and Nb₂O₅ photoanode, as shown by bathochromic shifts in wavelengths in the photosensitizer-loaded TiO₂, ZnO, and Nb₂O₅ photoanodes. FT-IR analysis also studied the bonding interaction between NO₂Lw and TiO₂, ZnO, and Nb₂O₅ photoanode material. The TiO₂, ZnO, and Nb₂O₅ photoanodes loaded with NO₂Lw exhibit a shift in the wavenumber of the functional groups, indicating that these groups were involved in loading the NO₂Lw photosensitizer. The amount of photosensitizer loading was calculated, showing that TiO₂ has higher loading than ZnO and Nb₂O₅ photoanodes; this factor may constitute an increased J_SC value of the TiO₂ photoanode. The device performance is compared using photocurrent-voltage (J-V) curves; electrochemical impedance spectroscopy (EIS) measurement examines the device's charge transport. The TiO₂ photoanode showed higher performance than the ZnO and Nb₂O₅ photoanodes in terms of photoelectrochemical properties. When compared to ZnO and Nb₂O₅ photoanodes-based DSSCs, the TiO₂ photoanode Bode plot shows a signature frequency peak corresponding to electron recombination rate toward the low-frequency region, showing that TiO₂ has a greater electron lifetime than ZnO and Nb₂O₅ photoanodes based DSSCs.