Electrodeposition of nanoporous ZnO on Al-doped ZnO leading to a highly organized structure for integration in Dye Sensitized Solar Cells

In the present study, we propose an improvement of the anode configuration in Zinc Oxide based Dye Sensitized Solar Cells (DSSC). Instead of the classical configuration, which is composed by two different metal oxides: one transparent conducting oxide (TCO) for the substrate and one nanostructured metal oxide for supporting the dye, the new approach is to use ZnO as unique material. Thus, nanoporous zinc oxide films have been electrodeposited on a sputtered Al doped ZnO layers with varying thicknesses up to 6 μm. The evolution of the porosity of the structure has been studied by scanning electron microscope (SEM) and electrochemical impedance spectroscopy and compared with standard nanoporous ZnO grown on fluorine doped tin oxide (SnO2:F noted FTO). This results firstly in the modification of the nanoporous structure morphology and secondly a better adhesion between the nanoporous layer and the substrate. Organization in the nanoporous material is enhanced with regular pores arrays and perpendicular to the substrate. Dye sensitized solar cells based on this simplified architecture present efficiencies up to 4.2% and 4.5% with N719 and D149 respectively as sensitizers. Higher fill factor and Voc are found in comparison with the one obtained for deposition on the classical transparent conducting oxide (FTO), which denote improved electrical transfer properties.