Geometrical isomerism of Ru(II) dye-sensitized solar cell sensitizers and effects on photophysical properties and device performances.

To supplement our study on thiocyanate-free ruthenium sensitizers (TFRS) for dye-sensitized solar cells (DSSCs), which belong to a class of Ru(II)-based complexes coordinated by a single 4,4'-dicarboxylic acid-2,2'-bipyridine and two symmetrically arranged functionalized trans-azolate chelates, we carefully isolated and characterized the second and less-abundant stereoisomer, in which the two pyridyl azolate ancillaries are asymetrically cis-arranged to each other. Two distinctive ancillaries, namely: 5-[4-(5-hexyl-2-thienyl)-2-pyridinyl]-3-trifluoromethyl pyrazole and 5-(6-tert-butyl-1-isoquinolinyl)-3-trifluoromethyl pyrazole, were employed in this study, giving a total of four sensitizers, that is, thienyl substituted TFRS-2 a and 2 b, and isoquinolinyl substituted TFRS-52 a and 52 b, in which the suffix b indicates the cis-stereoisomers. To gain insight into their fundamental properties their photophysical, electrochemical, and spectroelectrochemical behavior was investigated by density functional theory. Upon comparison of the correspondingly fabricated DSSCs, the sensitizers TFRS-2 a and 52 a yielded significantly higher conversion efficiencies than their asymmetrical cis-counterparts, TFRS-2 b and 52 b. To rationalize the cell performances charge extraction/photovoltage decay and impedance spectroscopic measurements were carried out to compare the rates of interfacial electron recombination from the TiO2 conduction band to the electrolyte.

Neutral copper(I) dipyrrin complexes and their use as sensitizers in dye-sensitized solar cells.

Heteroleptic neutral copper(I) dipyrrin complexes have been synthesised with the general formula [Cu(4,4'-(R)-6,6'-(CH3)-bipyridine)(dipyrrin)], R = CH3 or CO2Et, and H-dipyrrin is either 1,3,7,9-tetramethyldipyrromethene (HL1), 1,13-diphenyl-6,8-diisoindolemethene (HL2), or 1,13-diphenyl-3,11-di(trifluoromethyl)-6,8-diisoindolemethene (HL3). Improved stability was observed across the series , likely due to better steric constraints between the ligands. Visible light absorption has also been enhanced with a red-shift in absorption from 450 nm to 600 nm. Complex 3 shows photoluminescence lifetime in the order of nanoseconds suggesting singlet fluorescence which is supported by theoretical calculations. Study of the complexes as sensitisers in dye-sensitised solar cells was achieved by assembling the dye in situ on the surface of TiO2 in a series of steps (anchoring ligand followed by ancillary ligand and [Cu(CH3CN)4][BF4]. The highest efficiency achieved was 0.41% for the dye with HL3, attributed to better dye regeneration due to a more favourable oxidation potential.

Substituted [Cu(I)(POP)(bipyridyl)] and related complexes: synthesis, structure, properties and applications to dye-sensitised solar cells.

The synthesis and subsequent spectroscopic, electrochemical, photophysical and computational characterisation of a series of heteroleptic Cu(I) complexes of general formula: [CuPOP{4,4'(R)-bipyridyl}][BF(4)] and [CuPOP{4,4',6,6'(R)-bipyridyl}][BF(4)] is described (POP = bis{2-(diphenylphosphanyl)phenyl} ether; R = Me, CO(2)H, CO(2)Et. The steric constraint imposed by the POP ligand can impede distortion towards square planar geometry upon MLCT excitation or oxidation and this is explored in the context of varying substituents on the bipyridyl ligand. The insight gained opens new avenues for design of functional Cu(I) systems suitable for photophysical and photoelectrochemical applications such as sensitisers for dye-sensitised solar cells (DSSCs).