Effect of 1-Substituted 2-(Pyridin-2-yl)-1-Benzo[]imidazole Ligand-Coordinated Copper and Cobalt Complex Redox Electrolytes on Performance of Ru(II) Dye-Based Dye-Sensitized Solar Cells.

A comparative study has been attempted on 1-substituted 2-(pyridin-2-yl)-1-benzo[]imidazole ligand-coordinated copper and cobalt metal complex electrolytes Cu[nbpbi](PF), Cu[npbi](PF), Co[nbpbi](PF), and Co[npbi](PF) in dry acetonitrile coupled with both N3 and N719 dyes in dye-sensitized solar cell (DSSC) devices. Impressively, the copper metal sites coordinated with ligands nbpbi (L1) and npbi (L2) shift the redox potential about 190-200 mV and pave the way to achieve remarkably higher power current efficiency, which is clarified with cyclic voltammetry, electrochemical impedance spectrum, electron lifetime, and quasi Fermi-level experimental results. Overall efficiencies of 4.99, 4.82, 3.26, and 3.19% under 1 sun conditions (100 mW cm) were obtained for Cu[nbpbi](PF) and Cu[npbi](PF) electrolytes coupled with the sensitizers (N3 and N719 dyes), which are considerably higher than those acquired for devices containing the cobalt electrolytes. These results signify a record for copper complex-based electrolytes coupled with ruthenium dyes in liquid DSSCs. In particular, bulky acceptor 4-nitro benzyl moiety-substituted 2-(pyridin-2-yl)-benzimidazole (on the N-H position) (ligand L1)-coordinated copper metal complex electrolytes achieved higher efficiency, approaching a suitable redox potential of 0.68 V NHE. At the same time, the napthyl moiety-substituted 2-(pyridin-2-yl)-benzimidazole (ligand L2)-coordinated copper metal complex electrolytes showed less redox potential due to its donating nature. It was determined that the and PCE increment of the devices consisting of Cu[nbpbi](PF) electrolytes was mainly attributed to various factors such as higher chemical capacitance, larger charge, longer electron life time, a downward shift in the quasi Fermi level of TiO, the slow recombination process, and fast dye regeneration. These results make easily tunable metal complexes bearing a new sort of 1-substituted 2-(pyridin-2-yl)-1-benzo[]imidazole ligand-based electrolytes as very promising copper electrolytes for further improvements of extremely efficient liquid DSSCs.