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Impact of Molecular Charge-Transfer States on Photocurrent Generation in Solid State Dye-Sensitized Solar Cells Employing Low-Band-Gap Dyes
journal contribution
posted on 2014-07-31, 00:00 authored by Sai Santosh
Kumar Raavi, Pablo Docampo, Christian Wehrenfennig, Marcelo J. P. Alcocer, Golnaz Sadoughi, Laura
M. Herz, Henry J. Snaith, Annamaria Petrozza“Push–pull”
structures have been considered
a winning strategy for the design of fully organic molecules as sensitizers
in dye-sensitized solar cells (DSSC). In this work we show that the
presence of a molecular excited state with a strong charge-transfer
character may be critical for charge generation when the total energy
of the photoexcitation is too low to intercept accepting states in
the TiO2 photoanode. Though hole transfer to the 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene
can be very fast, an electron–hole pair is likely to form at
the organic interface, resulting in a possible traplike excitation.
This leads to poor photocurrent generation in the solid state DSSC
(ss-DSSC) device. We demonstrate that it is possible to overcome this
issue by fabricating SnO2-based ss-DSSC. The resulting
solar cell shows, for the first time, that a SnO2-based
ss-DSSC can outperform a TiO2-based one when a perylene-based,
low-band-gap, push–pull dye is used as sensitizer.