An efficient flexible dye-sensitized solar cell with a photoanode consisting of TiO2 nanoparticle-filled and SrO-coated TiO2 nanotube arrays

Three types of flexible dye-sensitized solar cells (DSSC) were fabricated, using as the photoanode an array of TiO2 nanotubes (TNT) or TiO2 nanotubes filled with TiO2 nanoparticles (TNT-TNP, particle size 14 nm) or TiO2 nanotubes not only filled with nanoparticles but also coated with a layer of strontium oxide (TNT-TNP-SrO). The nanotubes were obtained by electrochemical oxidation of a Ti sheet and their lengths (0.5 mm to 18.8 mm) were controlled by varying the anodization period from 0.25 to 18 h. The DSSC using titanium nanotube arrays as the photoanode (hereafter called TNT-DSSC) showed a solar-to-electricity conversion efficiency (eta) of 3.46%, when the anodization period was 12 h. When TNT-TNP was used as the anode, the efficiency of the DSSC (hereafter called TNT-TNP-DSSC) has increased to 4.56%. An efficiency of 5.39% was obtained when TNT-TNP-SrO was used as the photoanode for the DSSC (hereafter called TNT-TNP-SrO-DSSC). Our own dye, coded as CYC-B1 was used in all the cases. The morphologies of TNT and TNT-TNP were characterized by FE-SEM. XRD was used to characterize the TNT. Explanations on the photovoltaic performances of the DSSCs are substantiated by using electrochemical impedance spectra (EIS), incident photon to current conversion efficiency (IPCE) curves, and Mott-Schottky plots.