Synthesis of novel ruthenium sensitizers and their application in dye-sensitized solar cells

Ruthenium(II) complexes [Ru(L2)(NCS)2] (K8) and [Ru(L)(L9)(NCS)2] (K9) (where L = 4,4′-bis(carboxyvinyl)-2,2′-bipyridine and L9 = 4,4′-dinonyl-2,2′-bipyridine) were synthesized and characterized by spectroscopic and electrochemical techniques. The performance of K8 and K9 complexes as charge transfer photosensitizers in nanocrystalline TiO2-based solar cells was investigated. These complexes when anchored onto TiO2 films exhibit very efficient sensitization yielding 75 ± 5% incident photon-to-current efficiencies (IPCE) in the visible region using an electrolyte consisting of 0.6 M methyl-N-butyl imidazolium iodide, 0.05 M iodine, 0.1 M LiI and 0.5 M tert-butylpyridine in 50/50 (v/v) mixture of valeronitrile and acetonitrile. At one sun, the K8 complex gave a short circuit photocurrent density of 18 ± 0.5 mA/cm2, the open circuit voltage 640 ± 50 mV and fill factor of 0.75 ± 0.05, corresponding to an overall conversion efficiency of 8.64 ± 0.5%. Under similar conditions, the K9-sensitized solar cell gave a photocurrent density of 16.5 ± 0.5 mA/cm2, 666 ± 50 mV open circuit potential and 0.71 ± 0.05 fill factor yielding 7.81% ± 0.6% efficiency.