Aggregation behaviour and electron injection/recombination dynamics of symmetrical and unsymmetrical Zn-phthalocyanines on TiO2 film

Abstract

We have synthesized symmetrical and unsymmetrical Zn-phthalocyanine derivatives (PZnPc, MPZnPc and TPZnPc) for dye sensitized solar cells (DSSCs). Steady state and time-resolved absorption and fluorescence studies were performed in DMF solvent and on a TiO₂ surface. The mode and extent of aggregation (H- and J-aggregates) of ZnPc adsorbed on a TiO₂ surface were demonstrated. MPZnPc shows both H- and J-aggregation, while TPZnPc shows only H-aggregation. Moreover, the fluorescence of ZnP/TiO₂ was completely quenched and this was assigned to electron injection from excited ZnPc to TiO₂. Energy level calculations show both ZnPc deriviatives have enough driving force to inject electrons into the conduction band of TiO₂. Furthermore, the radical cation of ZnPc was observed in nanosecond transient absorption measurements.