Influence of the built-in voltage on the fill factor of dye-sensitized solar cells

Dye-sensitized solar cells with different front contact materials to the nanoporous TiO2 layer are used to investigate the influence of the front contact barrier on the photovoltaic performance. The study uses devices that have SnO2:F, ZnO:Al, Al, or An contacts underneath an amorphous TiO2 blocking layer and the nanocrystalline TiO2. These devices are illuminated via the semitransparent platinum back contact. Variations of the front contact have no significant influence on the open circuit voltage of the devices. In contrast, the fill factors of the solar cells exhibit systematic differences. The experimental current/voltage curves are fitted to a simple model that uses two diodes, one corresponding to the front contact/TiO2 interface and a second one for the TiO2/electrolyte interface.