Recent Investigations on Thiocyanate-Free Ruthenium(II) 2,2′-Bipyridyl Complexes for Dye-Sensitized Solar Cells

Abstract

Three decades ago, dye-sensitized solar cells (DSSCs) emerged as a method for harnessing the energy of the sun and for converting it into electricity. Since then, a lot of work has been devoted to create better global photovoltaic efficiencies and long term stability. Among photosensitizers for DSSCs, thiocyanate-free ruthenium(II) complexes have gained increasing interest due to their better stability compared to conventional thiocyanate-based complexes, such as benchmark dyes N719 and Z907. In this mini-review, two classes of thiocyanate-free Ru(II) complexes are presented: (a) bis-bipyridyl compounds bearing an ancillary cyclometalating bidentate ligand; (b) bipyridyl compounds bearing non-cyclometalating ancillary ligands. The coverage, mainly from 2014 up to now, is not exhaustive, but illustrates the most recent design strategies and photovoltaic properties of these two families of ruthenium(II) dyes.

Synthesis, Characterization, and Electrochemical Activities of Ruthenium(II) Bipyridyl-Dithiocarbamate Complexes

“…According to Mauri et al, one of the main complications of thiocyanate ancillary ligand is its ambidentate nature, due to its metal coordination property via the nitrogen or sulfur atom. Besides, it is to a certain extent labile and is easily replaced by other species in the International Journal of Photoenergy International Journal of Photoenergy complex, such as 4-tert-butylpyridine (TBP) which is usually involved as additive in the redox mixture [8]. To overcome this thiocyanate problems, many research groups have investigated the field of NCS-free bipyridine ruthenium(II) complexes employed as dyes in DSSC to replace the NCS ligands [8].…”

“…Besides, it is to a certain extent labile and is easily replaced by other species in the International Journal of Photoenergy International Journal of Photoenergy complex, such as 4-tert-butylpyridine (TBP) which is usually involved as additive in the redox mixture [8]. To overcome this thiocyanate problems, many research groups have investigated the field of NCS-free bipyridine ruthenium(II) complexes employed as dyes in DSSC to replace the NCS ligands [8]. All the ruthenium(II) complexes showed signal at 0.55-2.15 ppm due to the alkyl group, as similarly reported in the literature [26].…”

“…In consideration of other metals in complex form, ruthenium(II) complexes have tremendous attention as photosensitizers in DSSCs because of their promising photoelectrochemical characteristics and extraordinary stability in the oxidized state [1]. In addition, sensitizers based on ruthenium complexes have been reported to reach power conversion efficiencies of over 11% [4][5][6][7][8]. Ruthenium(II) polypyridyl sensitizers have been extensively used as effective sensitizers because of their intense charge transfer absorption in the visible region of the electromagnetic spectrum [8].…”

“…In addition, sensitizers based on ruthenium complexes have been reported to reach power conversion efficiencies of over 11% [4][5][6][7][8]. Ruthenium(II) polypyridyl sensitizers have been extensively used as effective sensitizers because of their intense charge transfer absorption in the visible region of the electromagnetic spectrum [8]. In support of the previous statement, recently, researchers have reported incorporated dithiocarbamate ligands in dye sensitizers that are able to stabilize transition metals in various oxidation states and to enhance the efficiency of ruthenium(II) sensitizers' systems [9,10].…”

Base-free synthesis of air- and moisture-stable Ru(III)-NHC complexes, [RuIII(PyNHCR)(Cl)3(H2O)] as precursors for Ru(II)-NHC complexes

“…The chemistry of coordination and organometallic complexes of ruthenium has continued to grow at unprecedented rates in the last few decades. [1][2][3][4] Ruthenium complexes have found applications in many industrial and scientific fields such as catalysis, [5][6][7][8] solar cells, 3 material sciences 9 and medicinal chemistry. 10 Ruthenium, the cheapest noble metal combined with its diverse applications, has attracted researchers from academia and industry to develop new Ru complexes with novel or improved properties and applications.…”