Structural Effect of the Pendant Unit in Thiocyanate‐Free RuII Sensitizers on the Dye‐Sensitized Solar Cell Performance

A combination of Ru complex sensitizers and Co complex redox couples for dye‐sensitized solar cells (DSSCs) generally results in low power conversion efficiency. This has been suggested to be from undesired electron transfer due to strong intermolecular interactions between the dye and the redox couple. To retard the interactions, two thiocyanate‐free ruthenium (Ru) sensitizers were synthesized with a terpyridine attached that has a triphenylamine (TPA) unit with branched alkoxy chains. The main difference between the two dyes is the angle of the three phenyl rings in the TPA unit. The DSSCs using both the new dyes show higher short‐circuit currents and open‐circuit voltages in comparison with those using a Ru complex dye with nonbranched alkyl chains. The Ru sensitizer with a more twisted TPA unit displays relatively high power conversion efficiency without coadsorption of chenodeoxycholic acid, suggesting less intermolecular interaction among dyes and thus also with Co complex redox couples. Two terpyridine‐based ligands 1 and 2 with different TPA structures were synthesized. Thereafter two thiocyanate‐free Ru dyes T11 and T12 were synthesized using 1 and 2 for use with DSSCs. The DSSCs using both the new dyes show higher short‐circuit currents and open‐circuit voltages in comparison with those using a Ru complex dye with nonbranched alkyl chains.