Abstract
The syntheses of 4,4′-bis(4-dimethylaminophenyl)-6,6′-dimethyl-2,2′-bipyridine (1), 4,4′-bis(4-dimethylaminophenylethynyl)-6,6′-dimethyl-2,2′-bipyridine (2), 4,4′-bis(4-diphenylaminophenyl)-6,6′-dimethyl-2,2′-bipyridine (3), and 4,4′-bis(4-diphenylaminophenylethynyl)-6,6′-dimethyl-2,2′-bipyridine (4) are reported along with the preparations and characterisations of their homoleptic copper(I) complexes [CuL2][PF6] (L = 1–4). The solution absorption spectra of the complexes exhibit ligand-centred absorptions in addition to absorptions in the visible region assigned to a combination of intra-ligand and metal-to-ligand charge-transfer. Heteroleptic [Cu(5)(Lancillary)]+ dyes in which 5 is the anchoring ligand ((6,6′-dimethyl-[2,2′-bipyridine]-4,4′-diyl)bis(4,1-phenylene))bis(phosphonic acid) and Lancillary = 1–4 have been assembled on fluorine-doped tin oxide (FTO)-TiO2 electrodes in dye-sensitized solar cells (DSCs). Performance parameters and external quantum efficiency (EQE) spectra of the DSCs (four fully-masked cells for each dye) reveal that the best performing dyes are [Cu(5)(1)]+ and [Cu(5)(3)]+. The alkynyl spacers are not beneficial, leading to a decrease in the short-circuit current density (JSC), confirmed by lower values of EQEmax. Addition of a co-absorbent (n-decylphosphonic acid) to [Cu(5)(1)]+ lead to no significant enhancement of performance for DSCs sensitized with [Cu(5)(1)]+. Electrochemical impedance spectroscopy (EIS) has been used to investigate the interfaces in DSCs; the analysis shows that more favourable electron injection into TiO2 is observed for sensitizers without the alkynyl spacer and confirms higher JSC values for [Cu(5)(1)]+.
Highlights
Future energy strategies will rely increasingly upon sustainable methods of energy generation in order to conform to the United Nations Sustainable Development Goals
The most widely deployed technologies are based upon semiconductor photovoltaics, but a promising methodology is the so-called dye-sensitized solar cell (DSC)
DSCs [1] convert solar to electrical energy using a wide-bandgap semiconductor such as nanoparticulate TiO2 functionalized with a material that absorbs visible light [2,3,4,5]
Summary
Characteristics and introducing alkynyl units to optimize electronic communication and conjugation oxidation and ligand-based reduction processes compared to the parent bis(2,3,7,8-tetramethyl-1,10has been found to be beneficial in some families of dyes [33] Most importantly, these beneficial weresubstituents gained without increases electron density lifetimes, on the metal centre and enhance the population of the metal-to-ligand loss in thethe long excited-state which result from the steric crowding imposed by the 2,3,7,8charge transfer (MLCT). 2,20 -Bipyridine ligands bearing phenylethynyl or 4-substituted-phenylethynyl substituents in the 4,40 or 5,5’-positions have been the focus of some attention, see for example [37,38,39,40], to the best of our knowledge, the use of related bis(diimine)copper(I) complexes in DSCs has not been explored.
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