## 3 Results and Discussion
The sp\({}^{2}\) sites of the carbon materials resulted in a \(\pi\)-\(\pi\  
The current density-voltage curves of DSSCs using closed-ended TiO\({}_{2}\) NTAs both with and without modification were measured under air-mass (AM) 1.5 sunlight, and the results are presented in Figure 5. The \(V_{\alpha}\), short-circuit current density (\(J_{\mathrm{sc}}\)), fill factor (_ff_), and energy conversion efficiency (n) of the DSSCs are summarized in Table 1. For the DSSCs without any treatment, the energy conversion efficiency was 4.10%, which increased to 5.73% when Ag NPs were embedded via UV irradiation (corresponding to an overall increase of 40%). When carbon materials were added to the closed-ended TiO\({}_{2}\) NTAs via CVD, the energy conversion efficiency improved to 5.69%, corresponding to a 39% increase. With both Ag NPs and carbon materials, the energy conversion efficiency further improved to 6.36%, corresponding to an overall increase of 55%. Note that when Ag NPs were treated with TiCl\({}_{4}\), the core-shell type Ag@TiO\({}_{2}\) nanoparticles were formed. Because the dye is adsorbed on Ag@TiO\({}_{2}\), the amount of dye loading may not be significantly reduced (Table 1). As previously reported, a large amount of carbon doping materials could lower the conversion efficiency by decreasing dye loading [25]. However, in this case, only a trace amount of carbon material was deposited, which did not significantly decrease the dye loading. Figure 4: Ultraviolet-visible (UV-Vis) spectrum of Ag NPs on the TiO\({}_{2}\) NTAs. Figure 5: Current density-voltage curves of DSSCs based on: (a) unmodified closed-ended TiO\({}_{2}\) NTAs, (b) embedded Ag NPs, (c) applied carbon materials, and (d) both Ag NPs and carbon materials. The current density-voltage curves for DSSCs based on open-ended TiO\({}_{2}\) NTAs with or without modification were also measured under AM 1.5 sunlight, and the results are presented in Figure 6. The \(V_{\alpha c}\), \(I_{sc}\), \(ff\) and \(\eta\) values of these DSSCs are summarized in Table 2. When unmodified TiO\({}_{2}\) NTAs were used, DSSCs based on open-ended TiO\({}_{2}\) NTAs had higher energy conversion efficiency (5.32%) compared to those based on closed-ended TiO\({}_{2}\) NTAs (4.10%). The closed-end barrier of the TiO\({}_{2}\) NTA disturbs electron transport between the TiO\({}_{2}\) layer and the electrode [17; 25]. When Ag NPs were embedded in the open-ended TiO\({}_{2}\) NTAs, the energy conversion efficiency improved from 5.32% to 6.14%, corresponding to a 15% enhancement. In this case, electron generation in the DSSCs was enhanced by the plasmonics from the NPs, despite the slightly diminished dye loading (from 153 to 151 nmol/cm\({}^{2}\)). When carbon materials alone were applied to TiO\({}_{2}\) NTAs, the energy conversion efficiency improved to 6.07% (a 14% increase). In this case, electron transport was improved due to the \(\pi\)-\(\pi\) conjugation across the small quantity of carbon materials in spite of a diminished dye load (153 to 147 nmol/cm\({}^{2}\), which was even less than with Ag NPs). Here carbon materials were distributed to interact with the TiO\({}_{2}\) and the dye, making up for the loss of dye loading in terms of the energy conversion efficiency. When Ag NPs and carbon materials were both applied to \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**DSSCs Based on Closed-Ended** & \(J_{sc}\) **(mA/cm\({}^{2}\))** & \(V_{oc}\) **(V)** & \(ff\) & \(\eta\) **(\%)** & **Dye Loading** \\
**TiO\({}_{2}\) NTAs Decorated** & & & & & \\ \hline without Ag NPs and carbon materials & 7.02 & 0.81 & 0.72 & 4.10 \(\pm\) 0.28 & 144 \\ with Ag NPs & 9.92 & 0.81 & 0.72 & 5.73 \(\pm\) 0.31 & 142 \\ with carbon materials & 10.03 & 0.80 & 0.71 & 5.69 \(\pm\) 0.26 & 139 \\ with Ag NPs and carbon materials & 11.25 & 0.80 & 0.71 & 6.36 \(\pm\) 0.34 & 141 \\ \hline \hline \end{tabular}
\end{table}