AVS 60th International Symposium and Exhibition
    Energy Frontiers Focus Topic Monday Sessions
       Session EN+AS+NS+SS-MoA

Paper EN+AS+NS+SS-MoA11
Plasmonic Sensing of Impregnation Kinetics of Dye Sensitized Solar Cells (DSSC)

Monday, October 28, 2013, 5:20 pm, Room 101 A

Session: Interfacial Challenges in Nanostructured Solar Cells
Presenter: B.H. Kasemo, Chalmers University of Technology, Sweden
Authors: V. Gusak, Chalmers University of Technology, Sweden
LP. Heiniger, Ecole Polytechnique Fédérale de Lausanne, Switzerland
V. Zhdanov, Boreskov Institute of Catalysis, Russian Federation
M. Graetzel, Ecole Polytechnique Fédérale de Lausanne, Switzerland
B.H. Kasemo, Chalmers University of Technology, Sweden
C. Langhammer, Chalmers University of Technology, Sweden
Correspondent: Click to Email
Dye sensitized solar cells (DSSCs) represent a low cost and environmentally friendly alternative to conventional Si solar cells. Recent advances (electrolyte and sensitizer) have resulted in a boost of their efficiency up to 13%. In DSSCs, interaction between dye molecules and the TiO2 electrode influences the device performance. The kinetics of impregnation of mesoporous TiO2 films with dye molecules is an important step in fabrication and key for potential mass production. Employing localized surface plasmon resonance (LSPR) sensing we explored the dye adsorption and impregnation process for flat TiO2 films and mesoporous TiO2 electrodes (1 - 10 µm thick) of the kind used as photoelectrodes in DSSCs. The flat films provide detailed monolayer adsorption - desorption kinetics that assist interpretation of the data from the complex mesoporous samples. For the latter the dye impregnation kinetics were followed, in real time, by a special version of LSPR sensing, Hidden Interface-Indirect Nanoplasmonic Sensing (HI-INPS) combined with optical absorption spectroscopy. The LSPR/HI-INPS technique employs plasmonic sensor nanoparticles embedded under the flat films or under the mesoporous TiO2 sample. In the former case this yields submonolayer sensitivity to dye molecule adsorption/desorption. For the mesoporous samples HI-INPS detects when dye molecules reach the "bottom" of the sample. The typical sensing range in this work was < 70 nm, a few percent or less of the mesoporous sample thicknesses. The measurements revealed an initial fast (minutes) and a later slow (>> 1hour) impregnation process (responsible for ca. 70 and 30 %, respectively, of the total uptake). The dye percolation time to the bottom of the 2 - 10 µm thick TiO2 photoelectrode films, was measured by HI-INPS for the dye Z907 in a mixture of acetonitrile and tert-butanol for different dye concentrations and for different thicknesses of the TiO2 sample. The total amount of adsorbed dye was simultaneously measured by optical absorption spectroscopy. The experimental data for the fast impregnation process were analyzed, with excellent agreement, by employing a diffusion-front model, combining diffusion and first order Langmuir type adsorption, which allows extracting the effective diffusion coefficient for the system. The latter value is about 15 µm2/s, an order of magnitude or more smaller than that for “free” diffusion of dye molecules in bulk solvents. The data from flat films, in addition to providing adsorption kinetics, also reveals that dye desorption and time dependent re-organization of dye molecules in the dye adlayer are significant processes.