Strongly coupled cyclometalated ruthenium triarylamine chromophores as sensitizers for DSSCs

Abstract

A series of anchor-functionalized cyclometalated bis(tridentate) ruthenium(II) triarylamine hybrids [Ru(dbp-X)(tctpy)](2-) [2a](2-)-[2c](2-) (H(3)tctpy=2,2';6',2 ''-terpyridine-4,4',4 ''-tricarboxylic acid; dpbH=1,3-dipyridylbenzene; X=N(4-C6H4OMe)(2) ([2a](2-)), NPh2 ([2b](2-)), N-carbazolyl [2c](2-)) was synthesized and characterized. All complexes show broad absorption bands in the range 300-700 nm with a maximum at about 545 nm. Methyl esters [Ru(Me3tctpy)(dpb-X)](+) [1a](+)-[1c](+) are oxidized to the strongly coupled mixed-valent species [1a](2+)-[1c](2+) and the RuIII(aminium) complexes [1a](3+)-[1c](3+) at comparably low oxidation potentials. Theoretical calculations suggest an increasing spin delocalization between the metal center and the triarylamine unit in the order [1a]2(+)<[1b](2+)<[1c](2+). Solar cells were prepared with the saponified complexes [2a](2-)-[2c](2-) and the reference dye N719 as sensitizers using the I-3(-)/I- couple and [Co(bpy)3](3+/2+) and [Co(ddpd)2](3+/2+) couples as [B(C6F5)(4)](-) salts as electrolytes (bpy=2,2'-bipyridine; ddpd=N,N'-dimethyl-N,N'-dipyridin-2-yl-pyridine-2,6-diamine). Cells with [2c](2-) and I-3(-)/I- electrolyte perform similarly to cells with N719. In the presence of cobalt electrolytes, all efficiencies are reduced, yet under these conditions [2c](2-) outperforms N719.