Functionalized phenyl bipyridine ancillary ligand as double recombination inhibitor in ruthenium complex for dye solar cells

• Bulky tert-butyl groups prevent aggregation and facilitate uniform monolayer.
• Alkyl chains reduce the recombination rates.
• MC219 showed better photo-voltage compared to standard N719.
• MC219 showed good thermal stability compared to standard N719 and Z907.
• Increased conjugation improved the molar extinction coefficient of the dye.

A simple ruthenium(II) polypyridyl complex Ru(II)(dcbp)(L)(NCS)2 coded as MC219, where dcbp = 4,4′-dicarboxylic acid-2,2′-bipyridine, L = 4,4′-bis(3,5-di-tert-butyl-4-(hexyloxy)phenyl)-2,2′-bipyridine has been synthesized and fully characterized with IR, NMR, MS, UV–Vis and electrochemical measurements. The incident photon to current conversion efficiency of MC219 reached its highest 56% at 550 nm. Under standard Air Mass (AM) 1.5 sunlight, the sensitizer MC219 yielded a short-circuit photocurrent density (JSC) of 9.58 mA cm−2, an open-circuit voltage (VOC) of 0.655 V, and a fill factor (ff) of 0.733, corresponding to an overall conversion efficiency of 4.6% compared to that of standard N719 at 7.2% (JSC of 18.43 mA cm−2, VOC of 0.582 V, ff of 0.671).