D-D-π-A organic dyes containing 4,4'-di(2-thienyl)triphenylamine moiety for efficient dye-sensitized solar cells.

Dye-sensitized solar cells (DSSCs) are currently under intense academic and industrial investigations, because of their environmentally-friendly, efficient, and low-cost features. The photosensitizer plays a key role in determining DSSCs' performance. The 4,4'-di(2-thienyl)triphenylamine moiety, included in dye TTC102, has been demonstrated before as a novel and efficient electron donor fragment. In this paper, the oversimple π-conjugated bridge of TTC102 was replaced by a 9-ethyl-3,6-di(2-thiophenyl)carbazole moiety. Two new D-D-π-A sensitizers, named TTC104 and TTC105, were synthesized and fully characterized. After anchoring on TiO(2) nanoparticle film, the absorption band of TTC104 is broader by 30 nm than that of TTC102. Under AM 1.5G irradiation, the energy conversion efficiency (η) of a DSSC based on TTC104 reaches 6.36%, which is 21.6% higher than that of TTC102 (5.24%). The results above demonstrate that the photovoltaic performance can be improved after introducing the 9-ethyl-3,6-di(2-thiophenyl)carbazole moiety to TTC102 when employed in DSSCs. Dye TTC105, containing a pyridyl group as the electron acceptor, showed only 1.88% conversion efficiency (η) when used in DSSCs. The huge different performances of TTC104 and TTC105 are proved to be partly due to the smaller dye loading amount, higher dark current and charge recombination rate of TTC105.