Cyclometalated Ruthenium(II) Complexes Featuring Tridentate Click‐Derived Ligands for Dye‐Sensitized Solar Cell Applications

A series of heteroleptic bis(tridentate) Ru(II) complexes featuring N^C^N-cyclometalating ligands is presented. The 1,2,3-triazole-containing tridentate ligands are readily functionalized with hydrophobic side chains by means of click chemistry and the corresponding cyclometalated Ru(II) complexes are easily synthesized. The performance of these thiocyanate-free complexes in a dye-sensitized solar cell was tested and a power conversion efficiency (PCE) of up to 4.0 % (Jsc =8.1 mA cm(-2) , Voc =0.66 V, FF=0.70) was achieved, while the black dye ((NBu4 )3 [Ru(Htctpy)(NCS)3 ]; Htctpy=2,2':6',2''-terpyridine-4'-carboxylic acid-4,4''-dicarboxylate) showed 5.2 % (Jsc =10.7 mA cm(-2) , Voc =0.69 V, FF=0.69) under comparable conditions. When co-adsorbed with chenodeoxycholic acid, the PCE of the best cyclometalated dye could be improved to 4.5 % (Jsc =9.4 mA cm(-2) , Voc =0.65 V, FF=0.70). The PCEs correlate well with the light-harvesting capabilities of the dyes, while a comparable incident photon-to-current efficiency was achieved with the cyclometalated dye and the black dye. Regeneration appeared to be efficient in the parent dye, despite the high energy of the highest occupied molecular orbital. The device performance was investigated in more detail by electrochemical impedance spectroscopy. Ultimately, a promising Ru(II) sensitizer platform is presented that features a highly functionalizable "click"-derived cyclometalating ligand.