Terpyridine and Quaterpyridine Complexes as Sensitizers for Photovoltaic Applications

Abstract

Terpyridine and quaterpyridine-based complexes allow wide light harvesting of the solar spectrum. Terpyridines, with respect to bipyridines, allow for achieving metal-complexes with lower band gaps in the metal-to-ligand transition (MLCT), thus providing a better absorption at lower energy wavelengths resulting in an enhancement of the solar light-harvesting ability. Despite the wider absorption of the first tricarboxylate terpyridyl ligand-based complex, Black Dye (BD), dye-sensitized solar cell (DSC) performances are lower if compared with N719 or other optimized bipyridine-based complexes. To further improve BD performances several modifications have been carried out in recent years affecting each component of the complexes: terpyridines have been replaced by quaterpyridines; other metals were used instead of ruthenium, and thiocyanates have been replaced by different pinchers in order to achieve cyclometalated or heteroleptic complexes. The review provides a summary on design strategies, main synthetic routes, optical and photovoltaic properties of terpyridine and quaterpyridine ligands applied to photovoltaic, and focuses on n-type DSCs.

Keywords: Ru(II) complexes; dye-sensitized solar cells; polypyridines; quaterpyridines; terpyridines.

Figure 1

Publications concerning the use of terpyridines (blue) and quaterpyridines (red) in DSCs. Source: SciFinder (January 2016) [15].

Figure 2

(a) Black Dye (BD) or N749 structure; (b) light absorption spectrum (red) and IPCE (black) [12] (Adapted from Ref 12 with permission of The Royal Society of Chemistry); and (c) crystal structure showing intermolecular hydrogen bonding [21] (Reprinted with permission from Nazeeruddin, M. K.; Péchy, P.; Renouard, T.; Zakeeruddin, S. M.; Humphry-Baker, R.; Comte, P.; Liska, P.; Cevey, L.; Costa, E.; Shklover, V.; Spiccia, L.; Deacon, G. B.; Bignozzi, C. A.; Grätzel, M. Engineering of efficient panchromatic sensitizers for nanocrystalline TiO₂-based solar cells. J. Am. Chem. Soc. 2001, 123, 1613–1624. Copyright 2001 American Chemical Society).

Figure 2

(a) Black Dye (BD) or N749 structure; (b) light absorption spectrum (red) and IPCE (black) [12] (Adapted from Ref 12 with permission of The Royal Society of Chemistry); and (c) crystal structure showing intermolecular hydrogen bonding [21] (Reprinted with permission from Nazeeruddin, M. K.; Péchy, P.; Renouard, T.; Zakeeruddin, S. M.; Humphry-Baker, R.; Comte, P.; Liska, P.; Cevey, L.; Costa, E.; Shklover, V.; Spiccia, L.; Deacon, G. B.; Bignozzi, C. A.; Grätzel, M. Engineering of efficient panchromatic sensitizers for nanocrystalline TiO₂-based solar cells. J. Am. Chem. Soc. 2001, 123, 1613–1624. Copyright 2001 American Chemical Society).

Figure 3

N719 structure.

Figure 4

Structure proposed by Wang et al. and N3 dye [71].

Figure 5

Complexes reported by Funaki et al. [72].

Figure 6

Complexes with one (4a) or two (4b) metal centers [74].

Figure 7

Terpyridine with a cyanoacrylic acid moiety [76].

Figure 8

4-Methylstyryl substituted and double-anchored tpy (HIS-2) [77].

Figure 9

Series of 5’’-substituted tpy proposed by Yang (7a-c) [78]; and Kimura (7d-g) [79].

Figure 10

4’ substituted Black Dye analogs [80].

Figure 11

Structures proposed by Ozawa et al. [82,83,84,85,86,87].

Figure 12

The first qtpy complex applied in DSCs by Renouard et al. [90].

Figure 13

Qtpy complexes investigated by Barolo et al. [68,91,92].

Figure 14

First example of tpy Ru-complex showing a bipyridine instead of two thiocyanates [25].

Figure 15

Monothiocyanate complexes proposed by Chandrasekharam [98] (top) and Giribabu [99] (bottom).

Figure 16

Bipyridine ancillary ligands with fluoren-2-yl or carbazol-3-yl substitutions [100].

Figure 17

Ancillary ligands modifications of complex 6 [101].

Figure 18

Four (23) and three (24) anchored complexes by Pavan Kumar [101] and Kanniyambatti [76].

Figure 19

Tpy extended with substituted stiryl moieties by Giribabu [102].

Figure 20

Bis-tpy complex proposed by Stergiopoulos et al. [106].

Figure 21

A first series of bis-tpy complexes proposed by Houarner et al. [107].

Figure 22

A structural variation of bis-py Ru complex proposed by Houarner et al. [109].

Figure 23

Modification of the BD structure with tris (t-butyl) tpy [100].

Figure 24

C^N bidentate ligands proposed by Funaki et al. for Ru(II)-complexes [116,117,118].

Figure 25

β-diketonates ligands by Islam et al. [119,120,121,122,123,124,125].

Figure 26

Pyridyl-pyrazolate ligand and quinolyl-bipyridine ligand for Ru(II)-complexes [22,127,128,129].

Figure 27

Tpy and phenyl-bipyridines complexes investigated by Wadman et al. [132].

Figure 28

Crystal structure of complex 37 in form of its dimer [132] (Adapted from Ref 131 with permission of The Royal Society of Chemistry).

Figure 29

Bis-tpy-based Ru(II) complex proposed by Kisserwan et al. [135].

Figure 30

Robson et al. [136] series of bis-tridentated ruthenium complexes bearing triphenyl amino groups.

Figure 31

Example of dipyrazinyl-pyridine ligand [135].

Figure 32

Triazolate ligand studied by Schulze et al. [140,141].

Figure 33

Ru(II) complexes proposed by Park et al. [142].

Figure 34

ORTEP drawing of complex 43b [142] (Reprinted with permission from Park, H.-J.; Kim, K. H.; Choi, S. Y.; Kim, H.-M.; Lee, W. I.; Kang, Y. K.; Chung, Y. K. Unsymmetric Ru(II) Complexes with N-Heterocyclic Carbene and/or Terpyridine Ligands: Synthesis, Characterization, Ground- and Excited-State Electronic Structures and Their Application for DSSC Sensitizers. Inorg. Chem. 2010, 49, 7340–7352. Copyright 2010 American Chemical Society).

Figure 35

Phosphine-coordinated Ru(II) sensitizer by Kinoshita et al. [144].

Figure 36

2,2’-Dipyrromethane by Li et al. [146].

Figure 37

Benzimidazole ligand tested by Swetha et al. [147].

Figure 38

Iron complexes reported by Duchanois [152].

Figure 39

NDI-Tpy proposed by Ji et al. [161].

Figure 40

“K1” structure proposed by Wood et al. [164].

Figure 41

D131 structure used in cosensitization [165,166].

Scheme 1

Retrosynthetic pathways to tpy core.

Scheme 2

Example of the Kröhnke pathway.

Scheme 3

Microwave-assisted synthesis of the trans-Ru (II) complex [68].