Impact of the Anchoring Ligand on Electron Injection and Recombination Dynamics at the Interface of Novel Asymmetric Push–Pull Zinc Phthalocyanines and TiO₂

Phthalocyanines are promising photosensitizers for dye-sensitized solar cells (DSSCs). A parameter that has been problematic for a long time involves electron injection (EI) into the TiO 2 . The development of push–pull phthalocyanines shows great potential to improve the ratio of EI to back electron transfer (BET). We have studied the impact of the anchoring ligand on EI and BET using transient absorption. The best performing derivative, which has a dicarboxylic acid anchoring ligand (TT15, DSSC efficiency of 3.96%), shows the fastest EI. The EI process occurs via an ultrafast component (∼700 fs for all derivatives) and a slower component (5.8 ps for TT15). The ps component is considerably slower for the other derivatives studied. Also BET depends on the anchoring ligand and is the slowest for TT15. This knowledge is essential for the optimization of the EI/BET ratio and the efficiency of a phthalocyanine-based DSSC.