The Impact of Molecular Charge-Transfer States on Photocurrent Generation in Solid State DSSCs Employing Low Band-Gap Dyes (original) (raw)
2014, The Journal of Physical Chemistry C
Push−pull" structures have been considered a winning strategy for the design of fully organic molecules as sensitizers in dyesensitized 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 TiO 2 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 SnO 2 -based ss-DSSC. The resulting solar cell shows, for the first time, that a SnO 2 -based ss-DSSC can outperform a TiO 2 -based one when a perylene-based, low-band-gap, push− pull dye is used as sensitizer. equally to this work. Figure 4. (a) Current/voltage characteristics under simulated solar conditions measured for ss-DSSC fabricated from either TiO 2 or SnO 2 nanoporous films sensitized with ID504 dye. As inset, the table reports the main figures of merit of the photovoltaic devices. (b) Photovolatic action spectra for TiO 2 -and SnO 2 -based DSSC incorporating ID504 as the sensitizer.
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