Controlling The Charge Transfer Dynamics in [Ru(bpy)2dppz]2+/NiO Interfaces by Ligand Design
in: ACS Applied Materials & Interfaces (2020)
Unravelling the mechanistic details of interfacial charge transfer in dyesensitized NiO photocathodes is essential for optimization of dye design with respect to solar energy application. This paper studies the interfacial charge transfer dynamics of a series of [Ru(bpy)2dppz]2+ complexes (bpy:2,2’-bipyridyne, dppz: dipyrido-phenazine) with phosphonic acid as anchoring group (Rudppz(L0)) immobilized on NiO films by timeresolved absorption and emission spectroscopy. In particular we discuss the effect of conjugated linkers on the charge transfer dynamics. Comparing extended bpy-ligands with phenylene (Rudppz(L1)) and triazole moieties (Rudppz(L2)), we show that different electronic effects are introduced . These effects cause the hole injection into the NiO to be ratecontrolled by interligand charge hopping within the coordination sphere of the Ru-sensitizer. Consequently the injection rate in the complexes is slower than in Rudppz(L0). Furthermore, the amplitude of the charge-separated state, formed upon hole injection, is highest for Rudppz(L0) and correlates with the observed photocurrents in dye-sensitized solar cells.