Excited-State Dynamics of [Ru(bpy) 3 ] 2+ Thin Films on Sensitized TiO 2 and ZrO 2

Abstract

The excited state dynamics of Tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate, [Ru(bpy) 3 (PF 6 ) 2 ], was investigated on the surface of bare and sensitized TiO 2 and ZrO 2 films. The organic dyes LEG4 and MKA253 were selected as sensitizers. A Stern–Volmer plot of LEG4-sensitized TiO 2 substrates with a spin-coated [Ru(bpy) 3 (PF 6 ) 2 ] layer on top shows considerable quenching of the emission of the latter. Interestingly, time-resolved emission spectroscopy reveals the presence of a fast-decay time component (25±5 ns), which is absent when the anatase TiO 2 semiconductor is replaced by ZrO 2 . It should be specified that the positive redox potential of the ruthenium complex prevents electron transfer from the [Ru(bpy) 3 (PF 6 ) 2 ] ground state into the oxidized sensitizer. Therefore, we speculate that the fast-decay time component observed stems from excited-state electron transfer from [Ru(bpy) 3 (PF 6 ) 2 ] to the oxidized sensitizer. Solid-state dye sensitized solar cells (ssDSSCs) employing MKA253 and LEG4 dyes, with [Ru(bpy) 3 (PF 6 ) 2 ] as a hole-transporting material (HTM), exhibit 1.2 % and 1.1 % power conversion efficiency, respectively. This result illustrates the possibility of the hypothesized excited-state electron transfer.