Fabrication of dye sensitized solar cells with improved multi-layer photonodes of hydrothermally grown TiO₂ nanocrystals in different autoclaving pHs

In this research dye sensitized solar cells (DSCs) with multilayer photopanodes made of small and large TiO₂ nanocrystals were fabricated. These nanocrystals were hydrothermally grown in two different basic autoclaving pHs of 10.0 and 12.0. The dominant sizes of TiO₂ NCs were measured about 15 and 70 nm for the growth in the mentioned pHs, respectively. The layers composed of 15 nm TiO₂ nanocrystals were well-transparent with high amount of dye adsorption. That is while the layers made of 70 nm TiO₂ nanoparticles demonstrated a high level of light scattering and lower amount of dye adsorption. Different multilayer photoanodes including one, two and three sub-layers of 15 nm TiO₂ nanocrystals and one over-layer of 70 nm TiO₂ nanoparticles were fabricated. Then the influence of the semi-scattering over-layer of the photanodes on the performance of corresponding DSCs was investigated. The results demonstrated that a maximum efficiency of 7.7% was achieved for a cell with a multilayer photoanode made of three sub-layers of small TiO₂ nanocrystals and one over-layer of 70 nm TiO₂ nanoparticles. This efficiency was increased about 16% compared to that of the cell with simple three layer photoanode. The reason was mainly attributed to the increased dye loading amount of the photoanodes with one semi-light scattering over-layer.