Highly efficient light harvesting ruthenium sensitizers for dye-sensitized solar cells featuring triphenylamine donor antennas

Two new heteroleptic ruthenium complexes, coded as KW1 and KW2, featuring triphenylamine electrondonating antennas, have been synthesized and used in dye-sensitized solar cells (DSSCs). Compared to the reference dye Z907, these new dyes exhibit broad absorption and efficient light harvesting properties. Particularly the KW2 dye exhibits a low-energy metal-ligand charge transfer band centred at 554 nm with a high molar extinction coefficient of 2.43 x 104 M-1 cm(-1) arising from an extended conjugation in the donor antenna ligand. Photovoltaic devices using these sensitizers in conjunction with a volatile electrolyte show high photovoltaic conversion efficiencies of similar to 10.7% under full sunlight irradiation (AM 1.5G, 100 mW cm(-2)). This efficiency is nearly 20% higher than that of the Z907-based reference device, which is attributed to a largely improved short circuit current. The distinct effects of different donor antennas incorporated in the ancillary ligands on the primary photovoltaic parameters in these devices are investigated with transient photoelectrical decays and impedance spectroscopy measurements. The devices utilizing these highly efficient light harvesting ruthenium sensitizers featuring triphenylamine donor antennas in combination with low volatility electrolytes exhibit good durability during the accelerated tests (60 degrees C for 1000 h in a solar simulator, 100 mW cm(-2)).