The solution was composed of 5 ml H2O and 0.1 mM NaOH. The films both had an area of 1 cm2. Figure 4 enables DAPT chemical structure the calculation of the dye loadings and the light absorptions at 370 and 530 nm (the dye’s absorption maximum) for both NRs and tree-like films. Compared

to the upstanding ZnO NRs film, the tree-like film shows an improvement in both light harvesting and dye loading. The Nyquist plots of the impedance spectra are shown in Figure 5. To characterize the ZnO/dye/electrolyte interface characteristics, the DSSCs were at V oc under AM 1.5 illumination by EIS measurement. The Nyquist plots (Figure 5) show a large semicircle at low frequencies and a small semicircle at high frequencies. As shown in Figure 5, they were fitted with an equivalent circuit alike to those reported in the literature. The equivalent circuit comprises R s (ohmic resistance), R ct1 (the Pt counter electrode), PRIMA-1MET manufacturer and R ct2 (ZnO/dye/electrolyte interfaces): (1) where τeff is the electron efficacious lifetime and f min is the frequency corresponding to the imaginary part minimum. R ct and τ eff are reported in Table 1. Here, it is shown that the interface area increases and R ct2 decreases for tree-like nanostructures. The electrochemical parameters were evaluated by fitting the EX 527 manufacturer experimental data with the equivalent circuit, as summarized in Table 1. The R CT2 value

for the photoelectrode containing a tree-like structure (95.8 Ω) is lower than that of the photoelectrode containing a nanorod structure (109.2 Ω), whereas the R CT1 value is almost the same. One possible cause for low-load transport resistance might be that axial charge transport in tree-like ZnO structures effectively obstructs the recombination progress with iodine

redox carriers [8]. Figure 3 Scanning electron microscopy images. SEM images of different ZnO nanostructures on FTO substrates. Side-view (a,c) and top-view (b,d) of vertically grown tree-like structures. Figure 4 Absorption spectra of DSSCs with ZnO nanostructures. Optical absorption spectra of D-719 dye-sensitized ZnO nanostructured electrodes. Figure 5 Analysis of electrochemical impedance spectroscopy. EIS of different ZnO nanostructure electrodes. Nyquist plots are used to measure under illumination (100 mA cm−2). Table 1 Electrochemical out and photovoltaic parameters of DSSCs Sample V oc (V) J sc (mA/cm2) FF R ct2 (Ω) τ eff (ms) Eff (%) NRs 0.661 0.699 0.397 109.2 3.23 0.203 Tree-like 0.680 0.784 0.413 95.8 3.91 0.231 Regarding branch-free rods, less accumulation on the electrode layer leads to poor electrolyte filling, improving the recombination pathway and raising the charge transport resistance. The surface charge density and trap level of the ZnO layer also play an important role in deciding the charge transport resistance by depleting the space charge layer.