Bilayer structured supramolecular light harvesting arrays based on zinc porphyrin coordination polymers for enhanced photocurrent generation in dye sensitized solar cells

An acylhydrazone zinc porphyrin P1 and its coordination polymers (CPs, denoted as P1M, M = Mn, Co, Ni, Cu, Zn) with different metal ions (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) were synthesized. Then these coordination polymers were assembled into bilayer structured supramolecular chromophores through axially coordinating with anchoring porphyrin AP, and their performance in dye sensitized solar cells was investigated. 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.