Rod-like Dinuclear Ruthenium Complexes for Dye-sensitized Photovoltaics
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Rod-like Dinuclear Ruthenium Complexes for Dye-sensitized Photovoltaics Ravi Mosurkal, Jin-An He, Jayant Kumar*, Lian Li1, John Walker2 and Lynne Samuelson2,* Center for Advanced Materials, University of Massachusetts, Lowell, MA 01854 1 Molecular Technologies Inc., Westford, MA 01886 2 Department of the Army, U.S. Army Soldier and Biological Chemical Command Natick Soldier Center, Natick, MA 01760 ABSTRACT Ruthenium complexes with tridentate terpyridine type ligands have many structural advantages over the complexes with bipyridine ligands. Polynuclear ruthenium complexes prepared using these terpyridine ligands bridged with phenylene rings are potential candidates for photosensitization in dye-sensitized photovoltaic cells. In this study, we have carried out synthesis, characterization and theoretical modeling of rigid, rod-like homometallic dinuclear ruthenium complexes using terpyridine and bipyridine ligands. The photophysical and photovoltaic properties have been investigated. These supramolecular dyes are found to be efficient photosensitizers in dye-sensitized photovoltaic cells when a liquid electrolyte is employed. INTRODUCTION There has been tremendous interest in the design and synthesis of novel photosentizers for their use in dye sensitized photovoltaic (DSPV) cells. Presently the most efficient and stable sensitizers are carboxylated polypyridyl complexes. Among them, [Ru(dcbpy)2(NCS)2] well known as N3 shows overall photo-to-electric conversion efficiency of ~10% when a liquid electrolyte containing I3-/I- solution is used [1]. The high efficiency in these DSPV cells is possible due to the nanoporous high surface area of TiO2 [2]. Though N3 dye has been the most efficient candidate, the absorption beyond 650 nm is very small. To utilize the full solar radiation, the dyes with absorption beyond 650 nm are necessary. Structural variations of Ru(II) complexes containing various polypyridyl ligands have been carried out by Gratzel et al [3]. Ferrere et al reported pure organic dyes[4] and Fe(II) complexes[5] as novel photosensitizers as alternative to conventional Ru(II) complexes. In an entirely different approach, dinuclear complexes, “dyads” have been found to be advantageous over mononuclear complexes due to the following reasons: (i) multinuclear systems can be easily synthesized with well-defined molecular lengths; (ii) these may provide fundamental insight into the interfacial electron transfer processes; and (iii) stabilization of photo-induced charge separation, multi-electron collection and antenna effects [6-7]. Homometallic dinuclear complexes using Ru and heterometallic complexes using Ru(II)/Rh(III) and other metals have been reported with strong internal energy and electron transfer processes [8]. Recently Kleverlaan et al studied stepwise charge separation in a multinuclear system containing Ru(II)/Rh(III) using bipyridyl ligands on nanocrystalline TiO2 films [9]. In the present study, we report the synthesis and photophysical properties of homometallic dinuclear Ru(II) complexes with bri
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