Design of OsII-based sensitizers for dye-sensitized solar cells: Influence of heterocyclic ancillaries

Abstract

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 H 2dcbpy 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. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.