Electron-Withdrawing Anchor Group of Sensitizer for Dye-Sensitized Solar Cells, Cyanoacrylic Acid, or Benzoic Acid?

High electron-injection efficiency is important for further development of dye-sensitized solar cells (DSSCs). Different electron acceptors have different electron-injection capabilities, which affect device performance. Herein, the effects of two organic triazatruxene (TAT)-based donor-pi-bridge-acceptor sensitizers applied in DSSCs are reported. The sensitizers have either rigid 4-ethynyl benzoic acid (EBA) or Z-type cyanoacrylic acid (CA) as their electron acceptor, denoted as ZL003 and ZL005, respectively. Time-resolved photoluminescence (TR-PL) spectroscopy is applied to reveal the electron transfer dynamics between the sensitizers and TiO2 films. Notably, ZL003 has higher electron-injection efficiency compared with that of ZL005, which is consistent with the higher efficiency and photocurrent of devices based on the former. The dye loading of ZL003 is nearly twice as great as that of ZL005, which accounts for the lower photocurrent of the device. The charge recombination lifetimes for the two dyes are consistent with their open-circuit voltage. Consequently, the ZL003-based devices achieve a higher power conversion efficiency of 13.4% compared with only 7.2% for ZL005.