Comparative Studies on the Structure-Performance Relationships of Phenothiazine-Based Organic Dyes for Dye-Sensitized Solar Cells.

A D-A-π-A dye () has been synthesized by introducing a benzothiadiazole (BTD) unit as an auxiliary acceptor in a phenothiazine-based D-π-A dye() to broaden its spectral response range and improve the device performance. Photophysical properties indicate that the inclusion of BTD in the effectively red-shifted the absorption spectra by reducing the . However, the device measurements show that the open-circuit voltage ( ) of cell (640 mV) is obviously lower than that of the cell (710 mV). This results in a poor photoelectric conversion efficiency (PCE) (4.43%) compared to that of cell (5.53%). Through further comparative analysis, we found that the introduction of BTD increases the dihedral angle between the D and A unit, which can reduce the efficiency of intramolecular charge transfer (ICT), lead to a less and lower molar extinction coefficient of . In addition, the ESI test found that the lifetime of the electrons in the cell is shorter. These are the main factors for the above unexpected result of PCE. Our studies bring new insights into the development of phenothiazine-based highly efficient dye-sensitized solar cells (DSSCs).