Physical properties of as-prepared and post-annealed TiO2 layers by atomic layer deposition and their cell performance

We report on the physical properties of TiO2 blocking layers with various thicknesses in both the as-prepared and the post-annealed states and on their cell performances in dye-sensitized solar cells (DSSCs). The TiO2 layers of various thicknesses (up to 50 nm) were prepared on fluorine-doped SnO2/glass substrates by using atomic layer deposition. The electron lifetime of the DSSCs was observed to depend critically on both the thickness and the annealing treatment for TiO2 layers with thicknesses up to 10 nm. However, for thicknesses above 20 nm, the cell performance of the DSSCs decreased because of increases in the defect density and charge recombination. We conclude that the cell efficiency of DSSCs with a 10-nm-thick TiO2 layer is higher than those of DSSCs with layers of other thicknesses; in addition, the cell characteristics of the post-annealed structures were better than those of the as-prepared ones.