Charge Transport in Dye-Sensitized Solar Cells Based on P25 TiO2 and Amorphous-Free P25 Photoanodes

Previously we demonstrated that the elimination of the amorphous component in commercially available TiO2 (P25) has a favorable influence on performance of dye sensitized solar cells (DSCs). The photo-conversion efficiency (PCE) of DSCs based on hydrothermally treated, amorphous-free P25 (H-P25), sensitized with a commercial organometallic dye (N719), was significantly enhanced (5.3%) compared to those based on untreated P25 (3.2%), due to an increased the photocurrent (Jsc), along with a substantially better fill factor (FF). Herein, the performance of DSCs based on H-P25 was further optimized by applying TiCl4 surface treatment on the photoanodes prior to devices assembly. The PCEs were enhanced after TiCl4 surface treatment to (6.2%) and (4.3%) for H-P25 and P25 devices respectively. These enhancements were attributed to the enhancement of Jsc and FF due to the removal of amorphous barriers and associated defect states as well as suppressing the electron recombination at (photoanode/dye/electrolyte) interfaces after being treated by TiCl4. In order to further investigate the reasons for the rises in Jsc and FF, even for devices made with the amorphous free H-P25 material, electron diffusion length, transient photocurrent, photovoltage decay and Mott- Schottky measurements were employed and studied along with photovoltaic device performance. The results indicated that DSCs based on H-P25 photoanode treated with TiCl4 showed a significant improvement on the charge collection and injection efficiencies and thus on PCE compared to DSCs based on pristine P25. The fact that a substantial improvement is seen even after the removal of amorphous TiO2. It is also interesting to compare the ways in which TiCl4 enhances performance for the two base materials.