HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 253
C116 - Atomic level characterization of D35/TiO2 interfaces - co-sensitization and
thermal degradation
Johan Oscarsson a , Rebecka Schölin a , Susanna K Eriksson b , Kristofer Fredin c , Erik M. J.
Johansson b , Håkan Rensmo a
a, Department of Physics and Astronomy, Uppsala University, Box 516, Uppsala, SE-751 20, Sweden
b, Department of Chemistry, Ångström, Uppsala University, Box 259, Uppsala, SE-751 05, Sweden
c, Department of Applied Physical Chemistry, Royal Institute of Technology, Teknikringen 30, Stockholm, SE-100 44, Sweden
To understand the performance of a dye in a dye‐sensitized solar cell (DSC) the properties of
the surface molecular- and electronic structures are very important. Photoelectron
spectroscopy (PES) gives information about binding geometry and energy levels in the dye
molecules versus TiO2. The surface sensitivity of the method being in the order of 20 Å makes
photoelectron spectroscopy a suitable tool for studies on the dye/semiconductor interface at
an atomic level.
Here we present results from studies on the sensitizer D35 regarding co-sensitization
with a Ruthenium based dye (RD) as well as effects of thermal treatment on the molecular
level.
Co‐sensitization is used to improve the light harvesting efficiency of the DSC by utilizing
dyes with different absorption properties. The study of D35 co‐sensitized with RD is based on
two different approaches for dying the porous TiO2 electrodes. In the first the electrodes are
first sensitized with RD and thereafter with D35 whereas the second approach relates to
simultaneous adsorption of RD and D35 in a solution comprising a 2:1 concentration ratio of
the respective dyes. The two dyes are clearly distinguishable in the PES measurements and the
results give information of the adsorption dynamics and how different mixing affect the
surface structure.
Because the DSC preparation scheme may contain steps involving heat treatment (1) it is
important to obtain information about the thermal stability of the utilized dyes. Here we
present results on D35/TiO2 interfaces (dye-sensitized electrodes) subjected to elevated
temperatures in an ambient air atmosphere. The results indicate that the dye molecules
transform into a single new compound at higher temperatures, which may affect the
performance of the DSC. The results also indicate that D35 can adsorb to TiO2 in different
ways. Already at lower temperatures the relative amounts of the two kinds of adsorption are
affected.
References
[1] Fredin, K.; Johansson, E. M. J.; Hahlin, M.; Schölin, R.; Plogmaker, S.; Gabrielsson, E.; Sun, LC. and Rensmo, H.
“Solid state dye‐sensitized solar cells prepared by infiltrating a molten hole conductor into a mesoporous film at a
temperature below 150 degrees C”. Synthetic metals 161, 2280-‐2283 (2011).
© SEFIN 2012