Double-layer novel zinc porphyrin based on axial coordination self-assembly for dye-sensitized solar cells

Porphyrin sensitizers have attracted great attention due to their admirable performance in dye-sensitized solar cell (DSSC). In this work, three antenna zinc porphyrins ZnPi (i = 1–3) and anchored porphyrin ZnPA have been designed, synthesized, and characterized. The antenna molecules ZnPi adhere on to the anchored porphyrin ZnPA via metal–ligand axial coordination self-assembly, and then the ZnPA bonding to nanostructured TiO2 to prepared ZnPi(i = 1–3)-ZnPA based DSSCs. Optical performance analysis showed that the devices based on self-assemblies exhibited obviously enhanced light-harvesting ability than the monomer anchor molecule ZnPA. The photovoltaic results showed that, compared with the ZnPA-sensitized solar cell, the ZnPi(i = 1–3)-ZnPA-sensitized solar cells have higher short - circuit photocurrent density (Jsc). However, the open circuit voltage (Voc) of the self-assembled porphyrin-sensitized solar cells are lower than the ZnPA-sensitized solar cell, this is because of the increase of charge recombination rate of the self-assembled porphyrin-sensitized solar cells on the electrode. As a result, the devices based ZnPi (i = 1–3)-ZnPA exhibited enhanced photoelectric conversion efficiency (PCE) than monomer ZnPA-sensitized solar cell. Especially for the ZnP3-ZnPA-sensitized solar cell with a optimal PCE is 3.44%, indicating that the trifluoromethyl substituent of the antenna molecule ZnP3 porphyrin was a more suitable group. Additionally, density functional theory (DFT) calculations are used to further verify the test results of the assembled sensitized solar cells. Therefore, our new method, metal-ligand self-assembly strategy provides new ideas for the high-performance DSSC.