## 3 Results and Discussion

Table 1: Photovoltaic properties of dye-sensitized solar cells (DSSCs) based on closed-ended TiO\({}_{2}\) nanotube arrays (TiO\({}_{2}\) NTAs) with Ag nanoparticles (NPs) and/or carbon materials. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**DSSCs Based on Open-Ended TiO\({}_{2}\)** & \(J_{sc}\) **(mA/cm\({}^{2}\))** & \(V_{oc}\) **(V)** & \(ff\) & \(\eta\) **(\%)** & **Dye Loading** \\
**NTAs Decorated** & & & & & \\ \hline without Ag NPs and carbon materials & 9.12 & 0.81 & 0.72 & 5.32 \(\pm\) 0.36 & 153 \\ with Ag NPs & 10.61 & 0.81 & 0.71 & 6.14 \(\pm\) 0.46 & 151 \\ with carbon materials & 10.73 & 0.80 & 0.71 & 6.07 \(\pm\) 0.30 & 147 \\ with Ag NPs and carbon materials & 12.41 & 0.80 & 0.69 & 6.91 \(\pm\) 0.41 & 149 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Photovoltaic properties of DSSCs based on open-ended TiO\({}_{2}\) NTAs with Ag NPs and/or carbon materials. Figure 6: Current density-voltage curves of DSSCs based on: (a) unmodified open-ended TiO\({}_{2}\) NTAs, (b) embedded Ag NPs, (c) applied carbon materials, and (d) both Ag NPs and carbon materials. the open-ended TiO\({}_{2}\) NTAs, the energy conversion efficiency improved to 6.91%, corresponding to a 30% enhancement when compared to the unmodified open-ended TiO\({}_{2}\) NTAs. In this case, the Ag NPs and carbon materials produced additive effects with their respective plasmonics and \(\pi\)-\(\pi\) conjugations; this was in spite of a slightly reduced dye loading of 149 nmol/cm\({}^{2}\). Comparing the performance parameters in Table 2, the \(V_{oc}\) and \(\mathit{ff}\) decreased with treatment; the conduction band of the TiO\({}_{2}\) NTAs shifted down as shown in Figure S2, which in turn affected the \(V_{oc}\) and the charge recombination through electron density suppressing the \(\mathit{ff}\). However, the \(J_{sc}\) was increased by the plasmonic activity in conjunction with \(\pi\)-\(\pi\), which improved the energy conversion efficiency of the DSSCs. The DSSCs based on open-ended TiO\({}_{2}\) NTAs were characterized by EIS across the frequency range from 10\({}^{-2}\) to 10\({}^{6}\) Hz, as shown in Figure 7. The applied bias voltage was set at the \(V_{oc}\) with 10 mV of AC amplitude. The data were analyzed using an equivalent circuit (Figure 7 inset), and the fit parameters are listed in Table 3. The ohmic series resistance (R\({}_{8}\)) was due to the sheet resistance corresponding to the x-axis value where the first semicircle begins (on the left-hand side of Figure 7). The value of R\({}_{8}\) was similar with or without Ag NPs or carbon materials, indicating that the additional deposits did not affect the sheet's resistance to FTO or the current collector. The R\({}_{1}\) value is given by the sum of the small semicircle, which at high frequency was assigned to the parallel combination of resistances and the capacitances at the Pt-FTO/electrolyte and the FTO/TiO\({}_{2}\) interfaces. The R\({}_{2}\) value is given by the sum of the large semicircle at low frequency (associated with the resistance) and the capacitance at the dye-adsorbed TiO\({}_{2}\)/electrolyte interface, as well as the transport resistance. The values of R\({}_{1}\) without and with Ag NPs were approximately 5.58 and 5.54 \(\Omega\), respectively. However, the value of R\({}_{2}\) with Ag NPs (36.90 \(\Omega\)) was much lower than without Ag NPs (61.12 \(\Omega\)). More electrons were generated by plasmonic activities than were produced at the dye-adsorbed TiO\({}_{2}\)/electrolyte interface. As a result, the R\({}_{2}\) value was reduced in the presence of Ag NPs. The value of R\({}_{1}\) with carbon materials (5.07 \(\Omega\)) was less than for without or with Ag NPs (5.58 and 5.54 \(\Omega\), respectively), whereas the value of R\({}_{2}\) (36.40 \(\Omega\)) was less than without Ag NPs (61.12 \(\Omega\)). Electrons were better transported by \(\pi\)-\(\pi\) conjugation affected by the FTO/TiO\({}_{2}\) and dye-adsorbed TiO\({}_{2}\)/electrolyte interfaces.