Impact of Molecular Orientation on Lateral and Interfacial Electron Transfer at Oxide Interfaces

QUENTIN LOAGUE; NIKLAS D. KELLER; ANDRESSA V. MÜLLER; BRUNO MARTIN ARAMBURU-TROSELJ; RACHEL E. BANGLE; JENNY SCHNEIDER; RENATO N. SAMPAIO; ANDRE S. POLO; GERALD J. MEYER

ACS APPLIED MATERIALS & INTERFACES

AMER CHEMICAL SOC

Lugar: Washington; Año: 2023

1944-8244

Molecular dyes, called sensitizers, with a cis-[Ru(LL)(dcb)(NCS)2] structure, where dcb is 4,4′-(CO2H)2-2,2′-bipyridineand LL is dcb or a different diimine ligand, are among the most optimalfor application in dye-sensitized solar cells (DSSCs). Herein, a series of five dye sensitizers, three bearing two dcb ligands and two bearing one dcb ligand, were anchored to mesoporous thin films of conducting tin-doped indium oxide (ITO) or semiconducting TiO2 nanocrystallites.The number of dcb ligands impacts the surface orientation of the sensitizer; density functional theory (DFT) calculations revealed an ∼1.6 Å smaller distance between the oxide surface and the Ru metal center for sensitizers with two dcb ligands. Interfacial electron transfer kinetics from the oxide material to the oxidized sensitizer were measured as a function of the thermodynamic driving force. Analysis of the kinetic data with Marcus–Gerischer theory indicated that the electron coupling matrix element, Hab, was sensitive to distance and ranged from Hab = 0.23 to 0.70 cm–1, indicative of nonadiabatic electron transfer. The reorganization energies, λ, were also sensitive to the sensitizer location within the electric double layer and were smaller, with one exception, for sensitizers bearing two dcb ligands λ = 0.40–0.55 eV relative to those with one λ = 0.63–0.66 eV, in agreement with dielectric continuum theory. Electron transfer from the oxide to the photoexcitedsensitizer was observed when the diimine ligand was more easily reduced than the dcb ligand. Lateral self-exchange “hole hopping” electron transfer between surface-anchored sensitizers was found to be absent for sensitizers with two dcb ligands, while those with only one were found to hop with rates similar to those previously reported in the literature, khh = 47–89 μs–1. Collectively, the kinetic data and analysis reveal that interfacial kinetics are highly sensitive to the surface 0rientation and sensitizers bearing two dcb ligands are most optimal for practical applications of DSSCs.