HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 160
C45 - Excited-State Dynamics of Iron(II)-based Charge-Transfer Chromophores
Allison Brown a , Lindsey Jamula b , James McCusker b
a, Department of Chemistry-Ångström Laboratory, Uppsala University, P.O. Box 523, Uppsala, 75120, SE
b, Department of Chemistry, Michigan State University, 485 Chemistry, East Lansing, MI, 48823, USA
Dye-sensitized solar cells (DSCs) continue to be an important area of research in the quest
for next-generation energy conversion devices. Since Grätzel’s 1991 report on the topic, 1
ruthenium-based sensitizers have played a central role as chromophores in DSC technology.
Despite initial improvements in overall efficiency - and notwithstanding possible future
breakthroughs - such devices have an important practical limitation due to the low natural
abundance of ruthenium. Finding a replacement for ruthenium-based chromophores based on
earth-abundant materials constitutes the underpinning of our research efforts in the
development of new classes of sensitizers for DSCs. Motivated by a 10 7 -fold higher natural
abundance, isoelectronic valence configuration, and an initial report suggesting photocurrent
production in a (non-optimized) DSC, we are focusing on charge-transfer complexes of Fe(II) as
a first step toward scalable dye sensitized solar cells. 2
Figure 1 Variable temperature kinetic data for a series of substituted iron(II)terpyridyl complexes. Thermodynamic
values were determined by fitting to the Arrhenius equation.
Initial work from our group intimated that a very short (< 100 fs) charge transfer-state
lifetime was responsible (at least in part) for the 10 2 -fold lower cell efficiency observed by
Ferrere and Gregg. A series of iron(II) based terpyridyl complexes have been synthesized and
spectroscopically characterized in an effort to determine the reaction coordinate associated
with charge transfer state deactivation with the goal of designing new chromophores with
longer MLCT lifetimes. Time-resolved absoprtion spectroscopy revealed a correlation among
the structures of these compounds, the activation parameters for ground state recovery, and
the MLCT lifetimes. Possible origins of these correlations will be discussed, along with more
recent data on a new class of Fe(II) polypyridyl chromophores that appear to hold considerable
promise as sensitizers for semiconductor-based DSCs.
References
[1] ORegan, B.; Grätzel, M. "A LOW-COST, HIGH-EFFICIENCY SOLAR-CELL BASED ON DYE-SENSITIZED COLLOIDAL
TIO2 FILMS". Nature 353, 737-740 (1991).
[2] Ferrere, S.; Gregg, B. A. "Photosensitization of TiO2 by [Fe-II(2,2 '-bipyridine-4,4 '-dicarboxylic acid)(2)(CN)(2)]:
Band selective electron injection from ultra-short-lived excited states". Journal of the American Chemical Society
120, 843-844 (1998).
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