Preparation, Characterization and Photosensitizing Activities of Homoleptic Cu(II) Dithiocarbamates in TiO2-Based DSSC

Abstract

New homoleptic copper(II) dithiocarbamate complexes, [Cu(L1-L5)2] (L1=N-benzyl-N-4-bromobenzyl dithiocarbamate− Cu1; L2=N-benzyl-N-4-methoxybenzyl dithiocarbamate− Cu2; L3=4-N,N-diethylbenzyl-N-methyl dithiocarbamate− Cu3; L4=N-methyl-N-4-isopropylbenzyl dithiocarbamate− Cu4 and L5=N-3-pyridyl-N-4-bromobenzyl dithiocarbamate− Cu5) have been synthesized and characterized by elemental analysis, HRMS, IR and UV-Vis. spectroscopy, PXRD and cyclic voltammetry. The monomeric (1−3) and dimeric (4) structures have been elucidated by X-ray crystallography. In all four structures the copper atom has square planar geometry. In 3 and 4 existence of rare C−H⋅⋅⋅Cu intermolecular anagostic interactions have been detected in the solid state. All complexes were exploited as sensitizers for TiO2 photoanode based dye-sensitized solar cells (DSSC). When TiO2 anchored with these complexes was used as DSSC photoanode, significant light harvesting properties were observed with an exceptionally high light-to-electrical energy conversion efficiency (3.62%) shown by Cu3 complex. The extent of interfacial charge-recombination and electron lifetime was evaluated from the electrochemical impedance spectroscopy (EIS) studies. The better performance of Cu3 compared to other complexes was attributed to its structural features. All the complexes with σrt, 10−6-10−9 S cm−1 are weakly conducting but show semiconducting behaviour in the 303–383 K temperature range with Ea values of 0.20−0.90 eV. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim