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

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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 JSC 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.