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Abstract: A series of novel D–π–A hydrazone dyes (HB, HP, HF and HT) containing an N,N-diphenylhydrazone donor and 2-cyanoacetic acid acceptor linked by a different aromatic bridge (benzene, pyrrole, furan, and thiophene) have been designed and synthesized to evaluate the aromatic bridge effects on the photophysical, electrochemical and the photovoltaic properties of the hydrazone-sensitized TiO2 solar cells. Each of the hydrazone-based dyes exhibited different adsorption behavior, frontier molecular orbitals, and photovoltaic performance depending on the identity of aromatic π-conjugated bridges. Specifically, HP-sensitized TiO2 solar cell showed an obviously higher photocurrent, photovoltage, and power conversion efficiency than other three dyes. We interpret that these results were stemmed from light-harvesting abilities, the charge recombination rate and electron lifetime of different aromatic bridges. Optical spectroscopy, cyclic voltammetry, density functional theory calculations, electrochemical impedance spectra, and photovoltaic measurements were employed to support our proposal. With the addition of 1mM chenodeoxycholic acid (CDCA) as the coadsorbent, a maximum power conversion efficiency of a DSSC based on HP was 7.74% (J sc =16.17mA/cm2, V oc =0.69V, FF=0.694) under simulated AM 1.5G solar irradiation (100mW/cm2). This work suggests that N,N-diphenylhydrazone and N-(2-ethylhexyl) substituted pyrrole moieties can be used as an alternative and effective donor and π-conjugated bridge, respectively, in the construction of efficient D–π–A organic dyes. [Copyright &y& Elsevier]

Abstract: Three D–A′–π–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. [Copyright &y& Elsevier]