Effects of the acceptors in triphenylamine-based D-A′-π-A dyes on photophysical, electrochemical, and photovoltaic properties

Three D-A'-pi-A structural triphenylamine dyes (Dye 1, Dye 2, and Dye 3) with cyanoacetic acid or malononitrile as an electron acceptor (A) and fluorenone or 9-(dicyanomethylene)fluorene as an additional acceptor (A') have been designed and synthesized. Results revealed that both A and A' have great influence on the optical, electrochemical and photovoltaic properties. In comparison with Dye 3, the photovoltaic performance of Dye 1 is remarkably improved by replacing 9-(dicyanomethylene)fluorene with fluorenone as the additional acceptor. The power conversion efficiency of dye-sensitized solar cell based on the Dye 1 (5.33%) is four times higher than that of Dye 3(1.25%). The low efficiency of cell based on Dye 3 is mainly because the delocalization of the excited state is broken between the strong electron-withdrawing additional acceptor (9-(dicyanomethylene)fluorene) unit and cyanoacetic acid, which affects the efficient electron injection from Dye 3 to the conduction band of TiO2. (C) 2013 Elsevier B.V. All rights reserved.