Self-assemblies formed by isonicotinic acid analogues axially coordinating with zinc porphyrin via pyridyl unit: Synthesis and application in dye sensitized solar cells

A novel zinc porphyrin ZnP bearing a 1,3,5-triazine-2,4-diamine unit has been designed and synthesized in good yields to construct axial-coordinated assemblies (denoted as ZnP-Ai, i = 1, 2, 3 and 4) with different isonicotinic acid analogues (assigned as A1, A2, A3 and A4) through zinc-to-ligand axial coordination approach. Then these assemblies were grafted onto TiO₂ electrode surface to build dye sensitized solar cells. The performance of these cells also was examined. Photoelectrochemical measurements illustrate that all the assembly based cells have certain capabilities to export photocurrent. Especially, the ZnP-A2 assembly with a cyanoacrylic acid group based solar cell has the highest conversion efficiency of 0.81% with a J_SC of 3.0 mA/cm², a V_OC of 0.38 V, and a FF of 0.71 among these assembly based solar cells. Additionally, the UV-vis absorption, fluorescence spectra, density functional theory (DFT) calculations, transmission electron microscopy (TEM) and electrochemical impedance spectra (EIS) were performed to determine the photoelectric behavior as well as morphological structure on the TiO₂ surface modified by these assemblies.