Synthesis of phenothiazine-based di-anchoring dyes containing fluorene linker and their photovoltaic performance

• Novel A-D-π-D-A dyes based on phenothiazine were synthesized.
• Photovoltaic performance can be influenced by the π-linker significantly.
• A fluorene unit as π-linker can increase η due to increase of Jsc.
• A thiophene–fluorene–thiophene unit as π-linker decreases η due to π-stacking.

A new di-anchoring organic dye based on phenothiazine featuring A-D-π-D-A (acceptor-donor-π-linker-donor-acceptor) configuration with fluorene as the π linker was designed and successfully synthesized. Compared to the corresponding mono-anchoring D-A congener, this new dye exhibited a broader and stronger absorption in the light wavelength ranging from 400 nm to 600 nm and thus showed a more efficient photovoltaic performance for dye-sensitized solar cells (DSSCs). The overall power conversion efficiency (η) of this new dye in a sensitized solar cell amounted to 5.70%, which is 17% higher than that of the equivalent based counterpart (4.87%). On the other hand, the introduction of two thiophene units at position-2 and -7 of the fluorene unit gave another new dye with extended conjugation. This extended conjugation dye showed a higher molar extinction coefficient (ε), but exhibited π-stacked aggregation on the TiO2 surface, resulting in low efficiency of electron injection. The results indicate that the di-anchoring dye with fluorene as π linker is a promising candidate for efficient DSSCs.

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