Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 7, Issue 46, Pages 25741-25747Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.5b07211
Keywords
dye-sensitized solar cell; dye aggregation; electron recombination; fluorinated self assembled monolayer; surface engineering
Funding
- National Creative Research Initiative Center for Intelligent Hybrids [2010-0018290]
- IRTG program through National Research Foundation of Korea [2011-0032203]
- BK21 Plus Program - [Ministry of Education, Science, and Technology of Korea]
- Korea Center for Artificial Photosynthesis [2009-0093883]
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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., I-3(-), 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.
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