Exploring copper(I) and ruthenium(II) dyes for their use in dye-sensitised solar cells
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Date
28/11/2013Item status
Restricted AccessEmbargo end date
31/12/2100Author
Hewat, Tracy Elizabeth
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Abstract
Dye design is one of the most important and challenging areas in dye-sensitised solar cell
research. The purpose of the work in this thesis is to synthesise and characterise novel
ruthenium(II) and copper(I) dyes that will provide insight into the number of binding groups
required and the potential use of chromophoric ligands.
A series of four simple Ru(II) dyes have been synthesised with the general formula Ru(4,4’-
(R)-bipyridine)2(NCS)2 where R represents CH3 or CO2H. The study investigates the number
of acid groups required to successfully bind to TiO2 whilst maintaining efficient charge
injection. The series consists of one acid group, two acids, two acids on adjacent bipyridines,
and three acids groups. Dye uptake was studied via optical waveguide spectroscopy,
providing information on dye diffusion, adsorption and desorption kinetics, and surface
coverage. Interestingly, the two acid groups on adjacent ligands suggested poor/slow binding
to TiO2 surface and a high degree of dye aggregation in comparison to two acid groups on
the same ligand. The dye with three binding groups showed strong adsorption to TiO2 and
better dye coverage, resulting in a high efficiency. The complexes were all fully
characterised by electrochemistry, photoluminescence, absorption spectroscopy, DFT
calculations and solar cell performance testing.
To date, there has been limited exploration of copper(I) complexes as potential alternatives
to ruthenium(II) sensitisers, with even fewer publications reported for Cu(I) heteroleptic
species. The neutral complexes that were synthesised are of the general formula: Cu(4,4’-
(R)-6,6’-(CH3)-bipyridine)(β-diketonate) and Cu(4,4’-(R)-6,6’-(CH3)-bipyridine)(dipyrrin)
where R represents CH3 or CO2Et. Additional blocking groups on the ligands are introduced
to minimise structural change during oxidation or MLCT excitation. Improved stability and
reproducibility have been shown for complexes containing the dipyrrin ligand, likely due to
better steric constraints and better π-overlap with the bipyridine. There has also been a
remarkable improvement in light absorption, from 450 nm to 600 nm. In-situ solar studies
have been carried out on the Cu(4,4’-(R)-6,6’-(CH3)-bipyridine)(dipyrrin) series and a 0.41%
efficiency has been achieved. Computational studies supports the experimental data in which
the main transition appears to be ligand centred (dipyrrin) with a small MLCT contribution.