An insight into the controllable synthesis of Cd( ii ) complexes with a new multifunctional ligand and its application in dye-sensitized solar cells and luminescence properties

Based on a new design of 4-cyanobenzyl-based 1,2,4-triazole ligand 4-(1,2,4-triazolylmethyl) cyanobenzene (TMCB), a series of cadmium complexes 1-5' from a mononuclear to three-dimensional (3D) structure have been synthesized through hydro(solvo)thermal reactions; they were generally formulated as [Cd(TMCBA) sub(2)] sub(n) (1), [Cd(TMCB)(1,4-bda)(H sub(2)O)] sub(n) (2), {[Cd sub(2)(TMCB) sub(4)(1,4-bda) sub(2)(H sub(2)O) sub(2)] sub(n).3H sub(2)O} sub(n) (3), {[Cd(TMCB) sub(4)(H sub(2)O) sub(2)].(NO sub(3)) sub(2 ).(H sub(2)O) sub(2)} sub(n) (4), [Cd sub(1.5)(1,4-bda) sub(1.5)(DM F) sub(2)] sub(2n) (5) and [Cd sub(1.5)(1,4-bda) sub(1.5)(DM F) sub(2)] sub(2n) (5') (TMCBA = 4-(1,2,4-triazolylmethyl) benzoic acid, which is formed from the hydrolysis of TMCB; 1,4-H sub(2)bda = 1,4-benzenedicarboxylic acid; the difference between two genuine supramolecular isomers of 5 and 5' is the use of TMCB as the additive agent for the reaction). Complexes 1-5' exhibit tunable luminescence with emission maxima containing deep blue, blue, light blue, green and deep green region at 298 K or 77 K in both different solvents (polarity: DMSO > CH sub(3)OH > CHCl sub(3)) and solid state. Interestingly, the good thermal stability accompanied by their compensated adsorption to ruthenium complex N719 in the region of low wavelength, enabled 1 and 4 to serve as co-sensitizers in combination with N719 in dye sensitized solar cells (DSSCs). After co-sensitization with N719, the overall conversion efficiency of 1 and 4 were found to be 7.68% and 6.85%, which are 40.40% and 25.23% higher than that for DSSCs only sensitized by N719 (5.47%) under the same conditions, respectively. The improvement in efficiency is attributed to the fact that complexes 1 and 4 overcome the deficiency of N719 absorption in the low wavelength region of ultraviolet and blue-violet, offset competitive visible light absorption of I sub(3) super(-) and reduce charge recombination due to the formation of an effective cover layer of the dye molecules on the TiO sub(2) surface. As a result, the synthesized complexes are promising candidates as co-adsorbents and co-sensitizers for highly efficient DSSCs.