To deprotect or not to deprotect : phosphonate ester versus phosphonic acid anchor ligands in copper(I)-based dye-sensitized solar cells

The performances of n-type DSCs containing the heteroleptic copper(I) dyes [Cu(1)(dmbpy)]+ and [Cu(2)(dmbpy)]+ (1 = ((6,6′-dimethyl-[2,2′-bipyridine]-4,4′-diyl)bis(4,1-phenylene))bis(phosphonic acid);2 = tetraethyl ((6,6′-dimethyl-[2,2′-bipyridine]-4,4′-diyl)bis(4,1-phenylene))bis(phosphonate); dmbpy = 6,6′-dimethyl-2,2′-bipyridine) have been evaluated to determine whether or not deprotection of the phosphonate ester prior to assembly of the heteroleptic [Cu(Lanchor)(Lancillary)]+ dye is an essential step. Fully masked DSCs containing [Cu(1)(dmbpy)]+ with I3−/I− electrolyte show conversion efficiencies, η, of ≈2.1% compared to ≈0.3% for those containing [Cu(2)(dmbpy)]+ in which 2 may be partially deprotected in situ. Compound 2is a surprisingly effective ancillary ligand; DSCs containing [Cu(1)(2)]+ exhibit η ≈2%. EQE spectra for DSCs containing the dyes [Cu(1)(dmbpy)]+ and [Cu(1)(2)]+ are similar, showing broad bands with λmax around 460–480 nm and EQEmax = 40%.