Bis(phenothiazyl-ethynylene)-Based Organic Dyes Containing Di-Anchoring Groups with Efficiency Comparable to N719 for Dye-Sensitized Solar Cells.

A new series of acetylene-bridged phenothiazine-based di-anchoring dyes have been synthesized, fully characterized, and used as the photoactive layer for the fabrication of conventional dye-sensitized solar cells (DSSCs). Tuning of their photophysical and electrochemical properties using different π-conjugated aromatic rings as the central bridges has been demonstrated. This molecular design strategy successfully inhibits the undesirable charge recombination and prolongs the electron lifetime significantly to improve the power conversion efficiency (η), which was proven by the detailed studies of electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD). Under a standard air mass (AM) 1.5 irradiation (100 mW cm-2 ), the DSSC based on the dye with phenyl bridging unit exhibits the highest η of 7.44 % with open-circuit photovoltage (Voc ) of 0.796 V, short-circuit photocurrent density (Jsc ) of 12.49 mA cm-2 and fill factor (ff) of 0.748. This η value is comparable to that of the benchmark N719 under the same conditions.