In this work, we report the use of bulky substitutions in a new heteroleptic ruthenium(II) bipyridine complex, Ru(NCS)2LL', 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 VOC greater than 1 V in DSC. However, with conventional Ru(II)-polypyridyl complexes such as the C101 dye, similar increase in the VOC 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.

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 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.