Bilayer Self-assembled Supramolecular Dye Sensitized Solar Cells Based On Zinc Porphyrin Coordination Polymers

Porphyrins and their derivatives have superior advantages like intense absorption in the visible region,ease of adjusting the molecular structure for photoelectric properties as well as high photochemical and electrochemical stabilities,making them the high-potential candidates of DSSCs sensitizers.In this work,we have synthesized a zinc porphyrin ligand P1 featuring an acylhydrazone Schiff base structure,then its coordination polymers?CPs?with different metal ions(Mn²⁺,Co²⁺,Ni²⁺,Cu²⁺and Zn²⁺)were prepared.These porphyrin CPs are immobilized onto TiO₂ electrode surfaces through axially coordinating with anchoring porphyrin AP,to build bilayer structured supramolecular light harvesting arrays.Subsequently,the sensitized TiO₂ electrodes were fabricated into solar cells.The effect of different metal ions of the porphyrin CPs in DSSCs was tested.The FT-IR spectra,UV–Vis absorption,fluorescence spectra,SEM-EDS spectra,electrochemical impedance spectra?EIS?and charge extraction?CE?and transient photovoltage decay?TPD?measurements were performed to investigate the morphological structure and photoelectronic behavior on the TiO₂ surface modified by these assemblies.Our results reveal that the bilayer structured supramolecular chromophore based solar cells show significantly improved photocurrent conversion efficiency.Particularly,P1Mn and P1Zn based solar cells showed a relatively higher short circuit current density(J_SC)due to their broad absorption bands and remarkable light harvesting abilities.Meanwhile,the V_OC values of the cells fabricated with the bilayered chromophores slightly decreased.Electrochemical impedance spectroscopy?EIS?in combination with charge extraction?CE?and transient photovoltage decay?TPD?measurements indicates that the decreased V_OC resulted from the vigorous electron recombination and the downward shifted conduction band edge(E_CB)of titania.