New class of NCS-free cyclometalated ruthenium(II) complexes with 6-phenylpyridine-2-carboxylate for use as near-infrared sensitizers in dye-sensitized solar cells

Three examples, FT102, FT90, and FT117 of a new class of NCS-free cyclometalated ruthenium(II) complexes, Ru(tctpy)(O^N^C) (where O^N^C is a tridentate 6-phenylpyridine-2-carboxylate), were synthesized for use as near-infrared (IR) sensitizers in dye-sensitized solar cells (DSSCs). A tridentate donor ligand, 6-phenylpyridine-2-carboxylate was introduced in order to enhance the light harvesting efficiency in the longer wavelength region for the first time. Modifying the ligand improved the photovoltaic performance, and DSSCs sensitized with FT117 exhibited efficient panchromatic sensitization over the entire visible wavelength, extending into the near-IR region. The highest incident photon-to-current conversion efficiency (68%) was found at 600 nm, and the action spectrum onset was near 920 nm.