Bis(pyrazolyl)methane supported cobalt (II) complexes as sensitizers in dye-sensitized solar cells

Abstract

A series of eight cobalt(II)-based dyes was synthesised using pyrazole and bis(pyrazolyl) methane derivatives. The new dyes were equipped with suitable anchoring functionalities, such as, carboxylic acid or thiocyanate groups, either on the ligand backbone or as a co-ligand to the metal center. All the synthesized compounds were characterized by various spectro-analytical techniques. The HOMO and LUMO energy gap of the dye molecules were determined theoretically by using B3LYP method. The opto-electronic and electrochemical properties of the dyes were analyzed by UV–visible spectroscopy and cyclic voltammetry studies respectively. The photo sensitizing capacity of all the synthesized cobalt-complexes was determined with a help of solar cell constructed using dye-TiO2 coated FTO anode, platinum coated FTO cathode and an iodine based redox mediator. Among the tested compounds, complexes C8 and C9 which contain carboxylic anchoring groups exhibited the best performance.