Novel iridium complex with carboxyl pyridyl ligand for dye-sensitized solar cells: High fluorescence intensity, high electron injection efficiency?

Abstract

Novel iridium-based sensitizers Iridium(III) bis[2-phenylpyridinato- N, C 2′]-5-carboxylpicolinate) ( Ir1), Iridium(III) bis[2-(naphthalen-1-yl) pyridinato- N, C 2′]-5-carboxyl-picolinate) ( Ir2), Iridium(III) bis[2-phenylpyridinato- N, C 2′]-4,4′-(dicarboxylicacid)-2,2′-bipyridine ( Ir3) were synthesized for sensitization of mesoscopic titanium dioxide injection solar cells. By changing the ligand, the absorption spectra can be extended and molar extinction coefficient was enhanced. The dye-sensitized nanocrystalline TiO 2 solar cells (DSSCs) based on dye Ir3 showed the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 85%, a short-circuit photocurrent density ( J sc) of 9.59 mA cm −2, an open-circuit photovoltage ( V oc) of 0.552 V, and a fill factor ( ff) of 0.54, corresponding to an overall conversion efficiency of 2.86% under AM 1.5 sun light. Moreover, the HOMO and LUMO energy levels tuning can be conveniently accomplished by alternating the ligand. The high oxidative potential of Ir3 enables it to be used along with Br - / Br 3 - redox electrolyte and the photovoltage was found to be enhanced greatly.