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A series of tri-tert-butyl zinc(II) phthalocyanines (Pcs) substituted with pyridyl, carboxyl, or picolinic acid anchoring groups on the periphery were prepared. Photovoltaic (PV) studies on these dyes were carried out revealing some interesting features. In the case of the pyridyl-substituted Pcs, the PV properties were found to depend strongly on the the pyridyl substitution pattern (meta or para) and the number of pyridyl units at the macrocycle's periphery (one or two). For these four pyridyl- substituted Pcs, higher photovoltaic efficiencies were obtained for 1) the para-versus the meta-substituted Pcs, and 2) the mono-versus the bis-functionalized dyes. In order to improve the poor adsorption of the pyridyl-substituted Pcs onto TiO2, a new dye was tested bearing a picolinic acid unit. This moiety combines a carboxylic acid function, as a strong anchoring group for binding to TiO2, with an electron-withdrawing nitrogen atom for better electron injection into the semiconductor's conduction band. For this latter system, an improvement in the PV efficiency up to 2.1% was obtained.

Two ruthenium sensitizers TT-230 and TT-232 based on cyclopenta[2,1-b:3,4-b']dithiophene (CDT) were tested in dye-sensitized solar cells (DSSCs) using,a tri-iodide/iodide redox couple, and their performances compared to the benchmark Z907. Both dyes of general formula Ru(LL')(NCS)(2) feature the same 4.4'-dicarboxylic acid 2,2'-bipyridine moiety acting as the anchoring group (L) to attach the dye on the TiO2 surface, and two CDT subunits as ancillary groups (L' either directly-linked (11-230) or vinylene-linked (TT-232) to the bipyridine moiety. In comparison with TT-230, the it-extended conjugation in TT-232 caused significant redshift and broadening of the absorption bands. However, despite better light-harvesting properties, the DSSC device sensitized with TT-232 strikingly underperformed compared to TT-230 under same conditions (PCE = 3.2% and 6.1%, respectively). The use of co-adsorbent (CHENO) or surfactants did not help to improve the photovoltaic properties of TT-230, and resulted in a degradation of the overall efficiency of the cell. (C) 2014 Elsevier Ltd. All rights reserved.

The detailed synthesis and characterization of four ruthenium(II) complexes [RuLL(NCS)(2)] is reported, in which L represents a 2,2-bipyridine ligand functionalized at the 4,4 positions with benzo[1,2-b:4,5-b]dithiophene derivatives (BDT) and L is 2,2-bipyridine-4,4-dicarboxylic acid unit (dcbpy) (NCS=isothiocyanate). The reaction conditions were adapted and optimized for the preparation of these amphiphilic complexes with a strong lipophilic character. The photovoltaic performances of these complexes were tested in TiO2 dye-sensitized solar cell (DSSC) achieving efficiencies in the range of 3-4.5% under simulated one sun illumination (AM1.5G).

A series of eight Ru(II) heteroleptic complexes incorporating an ancillary [2,2′]bipyridine functionalised at the [4,4′] positions with one (M-type) or two (B-type) thienylenevinylenes (nTVs, n = 2 or 4) is reported. Three types of substitutions have been used for nTVs: hexylthioether, hexyloxy and hexyl. The characterisation of the half-sandwich intermediates and final complexes is provided. In particular, the half-sandwich complexes in the M-type series are obtained as a racemate, whereas the heteroleptic complexes consist of two regioisomers. Finally, these complexes have been tested as dyes in dye-sensitized solar cells (DSSCs). Counterintuitively, better performances were obtained for M-type complexes with shorter 2TV moieties. The best performing dye was the Ru(II) complex mono-functionalized with a 2TV moiety having an hexylthioether substitution (M2S), which achieved a maximum power efficiency of 2.77% under full sun illumination (AM1.5G standard conditions). The structure–performance relationship in DSSCs is discussed based on photovoltaic and electrochemical data and DFT-calculations.

In this work, we report the use of bulky substitutions in a new heteroleptic ruthenium(II) bipyridine complex, Ru(NCS)(2)LL', coded TT-230 to obtain high open-circuit potential in a dye-sensitized solar cell (where L is a bipyridine ligand appended with two cyclopenta(2,1-b;3,4-bA)dithiophene moieties, and L' = 4,4,'-dicarboxylic acid 2,2'-bipyridine). The electrolytes based on cobalt complexes have shown significant advantages in terms of attainable open-circuit potential compared to the standard iodide/tri-iodide redox mediators. These merits of the cobalt complexes were previously realized with a porphyrin sensitizer, achieving a V-OC greater than 1 V in DSC. However, with conventional Ru(II)-polypyridyl complexes such as the C101 dye, similar increase in the V-OC could not be attained due to the enhanced recombination. In this work, we have shown that the use of bulky substituents can prevent the back reaction of photogenerated electron and subsequently increase the open-circuit potential of the device. The recombination processes were investigated by transient photovoltage decay measurements.