Dye-sensitized solar cells based on TiO2 nanotubes and a solid-state electrolyte

Anatase TiO2 nanotubes were employed with success as photoanode in dye-sensitized solar cells (DSSC) using a plasticized polymer electrolyte based on a poly(ethylene oxide) derivative. The plasticized electrolyte, poly(ethylene oxide-co-epychlorohydrin) containing NaI–I2 had their conductivity and thermal behavior characterized as a function of the salt content. The highest ionic conductivity (5.5 × 10−4 S cm−1) was obtained with 12.5 wt% NaI and 50 wt% of the plasticizer poly(ethyleneglycol)dibenzoate. The TiO2 nanotubes were prepared by a simple sol–gel route and were characterized by FEG-SEM, TEM, XRD and BET. For the same film thickness, the DSSC assembled with the titania nanotubes had much higher efficiency in comparison with the device using TiO2 nanoparticles. Although the one-dimensional properties exhibited by these materials can improve the electronic transport, in this study we demonstrated that the increase in the DSSC performance may be much more closely related to the high surface area of the titania films. This more open structure allows much more dye to be chemically absorbed and also facilitates the penetration of the polymer electrolyte, improving the iodide diffusion inside the film. We also observed that it was necessary to introduce a film of nanoparticulated TiO2 prior deposition of the nanotubes in order to improve electrical contact with the conducting glass. Devices with efficiency of 4.03% at 100 mW cm−2 (Xe(Hg) lamp) can be obtained using a combination of TiO2 nanotubes and this plasticized polymer electrolyte.