Increased Efficiency of Dye-Sensitized Solar Cells by Incorporation of a Spacer in Donor-Acceptor Zinc Porphyrins Bearing Cyanoacrylic Acid as an Anchoring Group

Two novel porphyrins, ZnP(SP)CNCOOH and ZnPCNCOOH, bearing cyanoacrylic acid as an anchoring group were synthesized. Porphyrin ZnP(SP)CNCOOH contains a -conjugated spacer (SP) for improved electronic communication between the dye and the TiO2 electrode. The spacer bears polyethylene glycol chains to prevent dye aggregation and to enhance solubility of the dye. Electrochemical measurements and theoretical calculations suggest that both porphyrins are promising sensitizers for dye-sensitized solar cells (DSSCs), as their molecular orbital energy levels favor electron injection and dye regeneration. Solar cells sensitized by ZnP(SP)CNCOOH and ZnPCNCOOH show power conversion efficiencies of 7.61 and 5.02%, respectively. Photovoltaic measurements (J-V curves and incident photon to current conversion efficiency spectra) show that higher short-circuit current (J(sc)) and open-circuit voltage (V-oc) values are reached for the solar cell based on ZnP(SP)CNCOOH. This can be mainly ascribed to suppressed charge recombination, as indicated by their electrochemical impedance spectra.