Systematic analysis of TiO2 compact layer effect on the performance of dye-sensitized solar cells

Prevention of the charge recombination at the photoelectrode is an important consideration in performance improvement of dye-sensitized solar cells (DSSCs). TiO2 as a compact layer was deposited on the fluorine-doped tin oxide (FTO)/glass substrate by using a TiCl4 aqueous solution in this study. The deposited TiO2 compact layer films fired at fired at 500 °C for 30 min were formed as a crystalline anatase phase with stoichiometry. The surface coverage and thickness of the TiO2 compact layer increased as the TiCl4 treatment time increased. The TCL30 sample treated for 30 min showed higher open-circuit voltage (0.739 V), a higher short-circuit current density (10.398 mA/cm2), and a greater fill factor (68.22) with higher power-conversion efficiency (5.237%) than the bare cell without a compact layer. Especially, the TCL30 sample exhibited a 17% increase in photo conversion efficiency compared with the bare cell. The TCL30 sample also showed the lowest dark current density and longest electron lifetime, which indicates effective suppression of the charge recombination. Meanwhile, based on the study of the patterned-TiO2 compact layers, it was found that the charge recombination via FTO might be the predominant loss mechanism rather than the TiO2 route. The cell with less surface area of the FTO/electrolyte interface showed better performance. Consequently, it was found that the surface area of the FTO/electrolyte interface should be decreased to improve the performance of DSSCs by minimizing the charge recombination via FTO.