Advanced Cd II complexes as high efficiency co-sensitizers for enhanced dye-sensitized solar cell performance

This work reports on two new complexes with the general formula [Cd 3 (IBA) 3 (Cl) 2 (HCOO)(H 2 O)] n ( 1 ) and {[Cd 1.5 (IBA) 3 (H 2 O) 6 ]·3.5H 2 O} n ( 2 ), which can be synthesized by the reaction of Cd II with rigid linear ligand 4-HIBA containing imidazolyl and carboxylate functional groups [4-HIBA = 4-(1 H -imidazol-1-yl)benzoic acid]. Single-crystal X-ray diffraction analyses indicate that complex 1 is a 2D “wave-like” layer structure constructed from trinuclear units and complex 2 is just a mononuclear structure. Surprisingly, both complexes 1 and 2 appear as a 3D supramolecular network via intermolecular hydrogen bonding interactions. What's more, due to their strong UV-visible absorption, 1 and 2 can be employed as co-sensitizers in combination with N719 to enhance dye-sensitized solar cell (DSSC) performance. Both of them could overcome the deficiency of the ruthenium complex N719 absorption in the region of ultraviolet and blue-violet, and the charge collection efficiency is also improved when 1 and 2 are used as co-sensitizers, which are all in favor of enhancing the performance. The DSSC devices using co-sensitizers of 1 /N719 and 2 /N719 show an overall conversion efficiency of 8.27% and 7.73% with a short circuit current density of 17.48 mA cm −2 and 17.39 mA cm −2 , and an open circuit voltage of 0.75 V and 0.74 V, respectively. The overall conversion efficiency is 27.23% and 18.92% higher than that of a device solely sensitized by N719 (6.50%). Consequently, the prepared complexes are high efficiency co-sensitizers for enhancing the performance of N719 sensitized solar cells.