e., the sheet resistance below 100 Ω sq−1 can be used as electrode [16, 17]. The surface morphologies of pristine PEDOT:PSS film and TiO2-PEDOT:PSS composite

film are depicted in Figure 1a,b, respectively. As is shown in the two images, the surface of modified PEDOT:PSS film is almost smooth, while the TiO2-PEDOT:PSS composite film is rough and has a large surface area which is good for catalytic reduction of I3 −. In TiO2-PEDOT:PSS composite film, as shown in Figure 1b, the thin catalytic layer is composed of TiO2 nanoparticles, and their diameter ranges from 20 to 50 nm. These nanoparticles are uniformly dispersed in PEDOT:PSS, forming a network structure, beneficial for electron conduction. Therefore, the performance of DSSCs with TiO2-PEDOT:PSS/PEDOT:PSS/glass TNF-alpha inhibitor CEs could be greatly improved by the addition of TiO2 nanoparticles. Figure 1 SEM images of PEDOT:PSS film (a) and TiO 2 -PEDOT:PSS composite film (b). A typical EIS spectrum for a DSSC exhibits three semicircles in the Nyquist plot, as is shown in Figure 2a. Traditionally, the first semicircle in high-frequency region corresponds to charge transfer resistance (R ct) of the CE/electrolyte interface, while the find more second semicircle in the middle-frequency region represents charge transfer and recombination

resistance in the TiO2/dye network [18, 19]. The low-frequency semicircle is attributed SAHA mouse to the Nernst diffusion Montelukast Sodium impedance of the I−/I3 − redox couple. From Figure 2a, we can obviously see that the spectra of TiO2-PEDO:PSS/PEDO:PSS/glass CE has a smaller semicircle than that of the POEDT:PSS/FTO CE, which indicates that TiO2-PEDO:PSS/PEDO:PSS/glass

CE has a better catalytic activity than POEDT:PSS/FTO CE. The simulated values of series resistance (R s), charge tansfer resistance (R ct), and diffusion element (Z w1) of corresponding cells calculated by Zview software are shown in Table 1. The simulated R ct and Z w1 of TiO2-PEDO:PSS/PEDO:PSS/glass CE (1.51 and 4.02 Ω cm2, respectively) are lower than those of PEDOT:PSS/FTO CE (4.47 and 11.28 Ω cm2, respectively), indicating that the addition of TiO2 nanoparticles greatly improves the catalytic activity for the redox reaction. The R s value of TiO2-PEDOT:PSS/PEDOT:PSS/glass CE is higher than that of PEODT:PSS/FTO CE due to a lower conductivity of PEDOT:PSS layer than that of FTO substrate, and the result is in accordance with the conclusion from the sheet resistance. However, the R ct of TiO2-PEDOT:PSS/PEDOT:PSS/glass composite CE is lower than that of Pt/FTO CE (5.73 Ω cm2) which is opposite to the traditional standpoint that a smaller R ct may lead to a higher fill factor (FF) and η in photovoltaic performance. However, for TiO2-PEDOT:PSS/PEDOT:PSS/glass CE, the charge transfer of the CE/electrolyte interface is mainly illustrated by the second semicircle of the spectra. Similar findings have been reported by He et al. [20] and Roy-Mayhew et al.