"Surfaces-as-ligands, surfaces-as-complexes" strategies for copper(I) dye-sensitized solar cells

A series of TiO2-supported copper(I) dyes, [Cu(Lanchor) (Lancillary)]+ with Lancillary = 2,2′:4′,4″:2″,2‴-quaterpyridine (1), 4,4′-bis(6-methyl-[2,2′-bipyridin]-4-yl)-1,1′-biphenyl (2), or 4,4′-bis(6,6′-dimethyl-[2,2′-bipyridin]-4-yl)-1,1′-biphenyl (3), and Lanchor = (6,6′-dimethyl-[2,2′-bipyridine]-4,4′-diyl)bis(4,1-phenylene)bis(phosphonic acid) (4), has been assembled in a stepwise manner. DSSCs incorporating these dyes demonstrate the need for 6,6′-substituents in both ligands in [Cu(Lanchor) (Lancillary)]+; both JSC and VOC increase on going from [Cu(4) (1)]+ to [Cu(4) (2)]+ to [Cu(4) (3)]+. First, second and third generation dyes [(4){Cu(3)}n]n+ (n = 1, 2 or 3) have been assembled using the 'surfaces-as-ligands, surfaces-as-complexes' strategy, although the separation between sites of electron injection and hole transporting domains in the multinuclear complexes fails to enhance DSSC performance. Replacing Lancillary2 in [Cu(4) (2)]+ by the metalloligand {Ru(bpy)2(2)}2+ improves dye performance due to the better spectral response of the heteronuclear [Cu(4){(2)Ru(bpy)2}]3+ complex. This assembly approach presents a flexible method of tuning dye properties while retaining the surface-bound bis(diimine)copper(I) domain.