Co-sensitized dye-sensitized solar cells based on d¹⁰ coordinate complexes towards their optoelectronic properties

Three five-coordinate transition metal complexes [2,6-(PhNCMe) ₂C₅H₃NMCl₂·CH₃CN] (M = Zn, Cd, Hg) (named M1) have been assembled onto a nanocrystalline TiO ₂ film to prepare transition metal complex/N719 co-sensitized photoelectrodes for dye-sensitized solar cell applications. The metal center is chelated in a tridentate manner by the ligand and further coordinated by two chlorine atoms, resulting in distorted trigonal bipyramidal geometry. In the tandem structure of the TiO₂/M1/dye electrode, the M1 undergoes a re-organization of energy levels due to its single-crystal structure, which is advantageous to electron injection and hole recovery. The co-sensitized structure is proved to have a superior ability, when compared to a single N719 dye's influence on TiO₂. Therefore, co-sensitized solar cells based on TiO₂/M1/N719 electrodes yield a remarkably high photocurrent density (J_sc), open circuit voltage (V_oc) and energy conversion efficiency under standard global AM1.5 solar irradiation conditions, which are relatively higher than those for DSSCs using single organic sensitizers.