Wideband dye-sensitized solar cells employing a phosphine-coordinated ruthenium sensitizer

Low-cost renewable energies are necessary for the realization of a low-carbon society. Organic photovoltaics such as organic thin-film solar cells 1 , 2 and dye-sensitized solar cells (DSSCs) 3 , 4 are promising candidates for realizing low-cost solar cells. However, device efficiencies are still considerably lower than those of traditional inorganic solar cells. To improve organic photovoltaic performance, approaches are needed to extend the absorption of organic compounds to longer wavelengths. Here, we report efficient DSSCs that exploit near-infrared, spin-forbidden singlet-to-triplet direct transitions in a phosphine-coordinated Ru( II ) sensitizer, DX1. A DSSC using DX1 generated a photocurrent density of 26.8 mA cm −2 , the highest value for an organic photovoltaic reported to date. A tandem-type DSSC employing both DX1 and the traditional sensitizer N719 is shown to have a power conversion efficiency of >12% under 35.5 mW cm −2 simulated sunlight. Single and tandem dye-sensitized solar cells with high power-conversion efficiencies and large photocurrent densities are fabricated using a photosensitizer whose long wavelength absorption originates from a spin-forbidden single–triplet transition.