Design of OsII-based Sensitizers for Dye-Sensitized Solar Cells: Influence of Heterocyclic Ancillaries

A series of OsII sensitizers (TFOS‐x, in which x=1, 2, or 3) with a single 4,4′‐dicarboxy‐2,2′‐dipyridine (H2dcbpy) anchor and two chelating 2‐pyridyl (or 2‐pyrimidyl) triazolate ancillaries was successfully prepared. Single‐crystal X‐ray structural analysis showed that the core geometry of the OsII‐based sensitizers consisted of one H2dcbpy unit and two eclipsed cis‐triazolate fragments; this was notably different from the RuII‐based counterparts, in which the azolate (both pyrazolate and triazolate) fragments are located at the mutual trans‐positions. The basic properties were extensively probed by using spectroscopic and electrochemical methods as well as time‐dependent density functional theory (TD‐DFT) calculations. Fabrication of dye‐sensitized solar cells (DSCs) was then attempted by using the I−/I3−‐based electrolyte solution. One such DSC device, which utilized TFOS‐2 as the sensitizer, showed promising performance characteristics with a short‐circuit current density (JSC) of 15.7 mA cm−2, an open‐circuit voltage of 610 mV, a fill factor of 0.63, and a power conversion efficiency of 6.08 % under AM 1.5G simulated one‐sun irradiation. Importantly, adequate incident photon‐to‐current conversion efficiency performances were observed for all TFOS derivatives over the wide spectral region of 450 to 950 nm, showing a panchromatic light harvesting capability that extended into the near‐infrared regime. Our results underlined a feasible strategy for maximizing JSC and increasing the efficiency of DSCs. Heavyweight: A series of OsII‐based sensitizers are prepared and demonstrated to be suitable dyes for the fabrication of DSCs with the I−/I3− electrolyte solution. The panchromatic light harvesting capability of these sensitizers extends into the near‐IR region, which is achieved by simple replacement of RuII with the more reducible and heavier OsII metal. Our results underline an attainable strategy for producing DSCs with potential industrial applications.