Systematic investigation of the role of compact TiO2 layer in solid state dye-sensitized TiO2 solar cells

The preparation steps of solid state dye-sensitized nanocrystalline TiO2 solar cells are optimized with respect to the blocking TiO2 layer which is one of the essential layers in such a multi-layer solar cell. By varying the number of spraying cycles in the preparation of the blocking TiO2 films, a series of samples with increasing blocking layer thicknesses was prepared. Influence of the layer thickness on the surface morphology was examined using scanning electron microscope (SEM). The thickness and refractive index of the blocking layers were also investigated with ellipsometry measurements. A linear increase in TiO2 layer thickness with the number of spraying cycles was observed for repetitive spraying cycles between 6 and 30. To characterize the rectifying behavior of the blocking layer, cells with the structure, FTO/blocking TiO2/hole conductor/Au, were prepared and their Current (I)-voltage (V) properties investigated. Solid state solar cells were also prepared with different blocking layer thicknesses and their photovoltaic properties were investigated in order to study the influence of the blocking layer thickness on solar cell performance. From the results, an optimum number of ten spraying cycles (corresponding to a film thickness of 150 nm) for the preparation of blocking TiO2 is suggested to obtain the best rectifying behavior and best photovoltaic properties of the corresponding solar cells. The automated procedure of preparing the blocking layer guarantees reproducibility in obtaining constant thickness and quality of this crucial layer as seen in the current-voltage characteristics of the solar cells. (C) 2004 Elsevier B.V. All rights reserved.