In Situ Mapping of the Molecular Arrangement of Amphiphilic Dye Molecules at the TiO₂ Surface of Dye-Sensitized Solar Cells.
Amphiphilic sensitizers are central to the function of dye-sensitized solar cells. It is known that the cell's performance depends on the molecular arrangement and the density of the dye on the semiconductor surface, but a molecular-level picture of the cell-electrolyte interface is still lacking. Here, we present subnanometer in situ atomic force microscopy images of the Z907 dye at the surface of TiO2 in a relevant liquid. Our results reveal changes in the conformation and the lateral arrangement of the dye molecules, depending on their average packing density on the surface. Complementary quantitative measurements on the ensemble of the film are obtained by the quartz-crystal microbalance with dissipation technique. An atomistic picture of the dye coverage-dependent packing, the effectiveness of the hydrophobic alkyl chains as blocking layer, and the solvent accessibility is obtained from molecular dynamics simulations.
†EPFL STI IMX SUNMIL, Station 12, CH-1015 Lausanne, Switzerland.|‡Physics Department, Durham University, Durham DH1 3LE, United Kingdom.
Kislon
K
Voïtchovsky
§EPFL SB ISIC LCBC, BC, CH-1015 Lausanne, Switzerland.
Negar
N
Ashari-Astani
§EPFL SB ISIC LCBC, BC, CH-1015 Lausanne, Switzerland.
Ivano
I
Tavernelli
∥EPFL SB ISIC LPI, Station 6, CH-1015 Lausanne, Switzerland.
Nicolas
N
Tétreault
§EPFL SB ISIC LCBC, BC, CH-1015 Lausanne, Switzerland.
Ursula
U
Rothlisberger
†EPFL STI IMX SUNMIL, Station 12, CH-1015 Lausanne, Switzerland.
Francesco
F
Stellacci
∥EPFL SB ISIC LPI, Station 6, CH-1015 Lausanne, Switzerland.
Michael
M
Grätzel
∥EPFL SB ISIC LPI, Station 6, CH-1015 Lausanne, Switzerland.
Hauke A
HA
Harms
Z907; atomic force microscopy; dye-sensitized solar cells; liquid phase; molecular dynamics simulations