Heterodimetallic Ferrocenyl Dithiophosphonate Complexes of Nickel(II), Zinc(II) and Cadmium(II) as Sensitizers for TiO2-Based Dye-Sensitized Solar Cells

The formation, characterization, and dye sensitized solar cell application of nickel(II), zinc(II) and cadmium(II) ferrocenyl dithiophosphonate complexes were investigated. The multidentate monoanionic ligand [S(2)PFc(OH)](-) (L1) was synthesized. The reaction between metal salt precursors and L1 produced Ni(II) complexes of the type [Ni{S2P(Fc)(OH)}(2)] (1) (molar ratio 1:2), and a tetranickel(II) complex of the type [Ni-2{S2OP(Fc)}(2)](2) (2) (molar ratio (1:1). It also produced a Zn(II) complex [Zn{S2P(Fc)(OH)}(2)](2) (3), and a Cd(II) complex [Cd{S2P(Fc)(OH)}(2)](2) (4). Complexes 1-4 were characterized by H-1 and P-31 NMR, FTIR and elemental analysis, and complexes 1 and 2 were additionally analyzed by X-ray crystallography. The first examples of dye-sensitized solar cells (DSSCs) co-sensitized with ferrocenyl dithiophosphonate complexes 1-4 are reported. Co-sensitization with the ruthenium dye N719, produced the dye materials (3)-N719 (eta=8.30%) and (4)-N719 (eta=7.78%), and they were found to have a better overall conversion efficiency than the pure Ru N719 dye standard (eta=7.14%) under the same experimental conditions. The DSSCs were characterized using UV/vis, cyclic voltammetry, electrochemical impedance spectroscopy (EIS), photovoltaic- (I-V curves), and performing incident photon-to-current efficiency (IPCE) measurements.