The internal resistance was investigated by EIS. The impedance spectra of the cells prepared Selleck PF2341066 using various amounts of nanorods sintered at 850°C are presented in Figure 2. The semicircles are related to the electron transfer resistance and the tendency
of recombination at the TiO2/electrolyte interface . The arc decreased with increasing amount of nanorods until 7 wt.% and then increased. The 1-D nanorods improved the charge transport and decreased electron recombination by providing fast moving paths for electrons. Although 1-D nanostructured nanorods have been proven to deliver a higher short-circuit photocurrent density (J sc) than TiO2 nanoparticles, too many large rutile nanorods could become a barrier for the electrons due to the higher energy level of the rutile phase. Figure 2 Impedance spectra of the cells with the rutile nanorods. Figures 3 and 4 show the electron diffusion coefficients (D n) and lifetimes (τ r) of the rutile TiO2
nanorods as a function of J sc. The D n and τ r values were determined by the photocurrent and photovoltage transients induced by a stepwise SYN-117 cell line change in the laser light intensity controlled with a function generator. The trends of diffusion coefficients by TiO2 structures are known to be reasonably consistent selleck products with the resistances in the TiO2 film determined by EIS [22, 23]. In Figure 3, all the DSSCs with 1-D rutile nanorods have a higher J sc than the 0 wt.% TiO2 electrode. Table 1 shows that the diffusion coefficients of the electrode with the 1-D rutile nanorods are higher than those of the electrode without the nanorods. However, the value of the diffusion however coefficient at the electrode with 15 wt.% nanorods decreased due to the higher energy level of the rutile phase
in the nanorods. In Figure 4, the J sc of the electrode with the 1-D nanorods is also increased. The lifetime of the electrodes with rutile nanorods is relatively similar to the 0 wt.% electrode at 3, 5, and 15 wt.% and higher at 7 and 10 wt.%. The 1-D nanorods with the increased τ r values can provide an electron pathway. The improved diffusion coefficient and the provided electron pathway result in a synergistic effect that increases the J sc. Figure 3 Electron diffusion coefficients ( D n ) for the DSSCs with the 1-D rutile nanorods. Figure 4 Electron lifetimes ( τ r ) for the DSSCs with the 1-D rutile nanorods. Table 1 Diffusion coefficients and lifetime values of the DSSCs with 1-D rutile nanorods at 1-V light intensity 0 wt.% 3 wt.% 5 wt.% 7 wt.% 10 wt.% 15 wt.% Diffusion coefficient (cm2 s−1) 2.40E−05 3.03E−05 2.89E−05 2.76E−05 2.63E−05 1.99E−05 Lifetime (τ r) (ms) 70.9 70.9 70.9 75.5 75.5 70.9 Table 2 shows the performances of the DSSCs with the 1-D structured rutile nanorods. The J sc value increased with increasing amount of nanorods until 10 wt.% and then decreased at 15 wt.%. The conversion efficiency of the cells using the rutile-phase nanorods was improved depending on the amount of nanorods.