Phenothiazine conjugated bipyridine as ancillary ligand in Ru(II)-complexes for application in dye sensitized solar cell

Abstract A new high molar extinction coefficient ruthenium(II)-bipyridine complex “cis-Ru(4,4′-bis((E)-2-(10-decyl-10H-phenothiazin-3-yl)vinyl)-2,2′-bipyridine)(4,4′-dicarboxylic acid-2,2′-bipyridine)(NCS) 2 PTZ 1″ was synthesized through conjugation of phenothiazine unit with bipyridine and characterized by FT-IR, 1 H-NMR and ESI-MASS spectroscopes. Absorption measurements and time dependent-density functional theory (TD-DFT) calculations show increased spectral response for the ancillary ligand and the corresponding complex. The dye upon anchoring onto mesoporous nanocrystalline TiO 2 solar cells exhibited solar-to-electric energy conversion efficiency ( η ) of 3.77% short-circuit photocurrent density ( J SC ) = 7.79 mA/cm 2 , open-circuit voltage ( V OC ) = 640 mV, fill factor = 0.750) under air mass 1.5 sunlight, the reference Z 907 and HRS 1sensitized solar cells, fabricated and evaluated under identical conditions exhibited η -value of 7.02% ( J SC  = 15.25 mA/cm 2 , V OC  = 650 mV, fill factor = 0.705) and 3.05% ( J SC  = 8.20 mA/cm 2 , V OC  = 610 mV, fill factor = 0.620) respectively. The lower film absorption of PTZ 1on TiO 2 surface could be probably due to larger molecular diameter and planarity of phenothiazine prone to aggregate in solution as well as on TiO 2 surface. The DFT calculations show that the first three HOMOs of PTZ 1 have t 2g character as observed in case of Z 907, while HOMO-4 and HOMO-5 have π-orbitals with major component on phenothiazine moieties of L 1.