Amphiphilic ruthenium sensitizers and their applications in dye-sensitized solar cells

Amphiphilic ligands 4,4'-bis(1-adamantyl-aminocarbonyl)-2,2'-bipyridine (L-1), 4,4'-bis{5- N-[2-(3beta-cholest-5-en-3ylcarbamate-N-yl)-ethyl]aminocarbonyl}-2,2'-bipyridine (L-2), 4,4'-bis{5-{N-[2-(3beta-cholest-5-en-3-ylcarbamate-N-yl)-propyl]aminocarbonyl}}-2,2'-bipyridine (L-3), and 4,4'-bis(dodecan-12-ol)-2,2'-bipyridine (L-4) and their heteroleptic ruthenium(II) complexes of the type [Ru(II)LL1(NCS)(2)] (5), [Ru(II)LL3(NCS)(2)] (6), [Ru(II)LL3(NCS)(2)] (7), and [Ru(II)-LL4 (NCS)(2)] (8) (where L = 4,4'-bis(carboxylic acid)-2,2'-bipyridine) have been synthesized starting from dichloro-(p-cymene)ruthenium(II) dimer. All the ligands and the complexes were characterized by analytical, spectroscopic, and electrochemical techniques. The performance of these complexes as charge-transfer photosensitizers in nanocrystalline TiO2-based solar cells was studied. When complexes 5-8 anchored onto a 12 + 4 mum thick nanocrystalline TiO2 films, very efficient sensitization was achieved (85 +/- 5% incident photon-to-current efficiencies in the visible region, using an electrolyte consisting of 0.6 M butylmethylimidazolium iodide, 0.05 M I-2, 0.1 M Lil, and 0.5 M tett-butyl pyridine in 1:1 acetonitrile + valeronitrile). Under standard AM 1.5 sunlight, the complex 8 yielded a short-circuit photocurrent density of 17 +/- 0.5 mA/cm(2), the open-circuit voltage was 720 +/- 50 mV, and the fill factor was 0.72 +/- 0.05, corresponding to an overall conversion efficiency of 8.8 +/- 0.5%.