Surface Modification of TiO2 Photoanodes with Fluorinated Self-Assembled Monolayers for Highly Efficient Dye-Sensitized Solar Cells.
Dye aggregation and electron recombination in TiO2 photoanodes are the two major phenomena lowering the energy conversion efficiency of dye-sensitized solar cells (DSCs). Herein, we introduce a novel surface modification strategy of TiO2 photoanodes by the fluorinated self-assembled monolayer (F-SAM) formation with 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFTS), blocking the vacant sites of the TiO2 surface after dye adsorption. The F-SAM helps to efficiently lower the surface tension, resulting in efficient repelling ions, e.g., I3(-), in the electrolyte to decrease the electron recombination rate, and the role of F-SAM is characterized in detail by impedance spectroscopy using a diffusion-recombination model. In addition, the dye aggregates on the TiO2 surface are relaxed by the F-SAM with large conformational perturbation (i.e., helix structure) seemingly because of steric hindrance developed during the SAM formation. Such multifunctional effects suppress the electron recombination as well as the intermolecular interactions of dye aggregates without the loss of adsorbed dyes, enhancing both the photocurrent density (11.9 → 13.5 mA cm(-2)) and open-circuit voltage (0.67 → 0.72 V). Moreover, the combined surface modification with the F-SAM and the classical coadsorbent further improves the photovoltaic performance in DSCs.
Sanghyuk
S
Wooh
Department of Energy Engineering and Center for Next Generation Dye-Sensitized Solar Cells, Hanyang University , Seoul 133-791, Korea.
Tea-Yon
TY
Kim
Department of Energy Engineering and Center for Next Generation Dye-Sensitized Solar Cells, Hanyang University , Seoul 133-791, Korea.
Donghoon
D
Song
Yong-Gun
YG
Lee
Department of Energy Engineering and Center for Next Generation Dye-Sensitized Solar Cells, Hanyang University , Seoul 133-791, Korea.
Tae Kyung
TK
Lee
Max Planck Institute for Polymer Research , 55128 Mainz, Germany.|Institute for Physics, Johannes Gutenberg University , 55128 Mainz, Germany.
Victor W
VW
Bergmann
Max Planck Institute for Polymer Research , 55128 Mainz, Germany.|Institute for Physics, Johannes Gutenberg University , 55128 Mainz, Germany.
Stefan A L
SA
Weber
Institute of Advanced Materials (INAM), Universitat Jaume I , 12006 Castelló, Spain.
Juan
J
Bisquert
Department of Energy Engineering and Center for Next Generation Dye-Sensitized Solar Cells, Hanyang University , Seoul 133-791, Korea.
Yong Soo
YS
Kang
Kookheon
K
Char
dye aggregation; dye-sensitized solar cell; electron recombination; fluorinated self-assembled monolayer; surface engineering