Low temperature sintering of binder-containing TiO2/metal peroxide pastes for dye-sensitized solar cells

Abstract

Nano-structured metal oxide films are key components of dye-sensitized (DSC) solar cells. Scaling such devices requires lower temperature processing to enable cheaper substrates to be used. In this context, we report a new and scalable method to sinter binder-containing metal oxide pastes to make DSC photo-electrodes at lower temperatures. Metal peroxide powders (CaO₂, MgO₂, or ZnO₂) were added to terpineol-based P25 pastes containing ethyl cellulose binder or to commercial TiO₂ paste (DSL18NR-T). Thermal analysis shows that binder decomposition occurs at 300 °C instead of the standard 450 °C for a TiO₂-only paste and suggests that the metal peroxides act as combustion promoters releasing heat and oxygen within the film while heating. The data show that this heat and oxygen release coincide best with binder combustion for ZnO₂ and DSC device tests show that adding ZnO₂ to TiO₂ pastes produces the best performances affording η = 7.5% for small devices (0.26 cm²) and η = 5.7% at 300 °C or 450 °C for DSL18NR-T/ZnO₂ for larger (1 cm²) devices. To the best of our knowledge, the performance of the (0.26 cm²) cells is comparable to the highest efficiency devices reported for DSCs fabricated using low temperature methods. The device efficiency is most strongly linked with J_sc; BET and dye sorption measurements suggest that J_sc is linked with the metal oxide surface area and dye loading. The latter is linked to the availability of surface sorption sites for dye molecules which is strongly negatively affected by any residual organic binder which resulted from incomplete combustion.