Ultrafast
Charge-Transfer Dynamics at the Boron Subphthalocyanine
Chloride/C<sub>60</sub> Heterojunction: Comparison between Experiment
and Theory
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Abstract
Photoinduced charge-transfer (CT)
processes play a key role in
many systems, particularly those relevant to organic photovoltaics
and photosynthesis. Advancing the understanding of CT processes calls
for comparing their rates measured via state-of-the-art time-resolved
interface-specific spectroscopic techniques with theoretical predictions
based on first-principles molecular models. We measure charge-transfer
rates across a boron subphthalocyanine chloride (SubPc)/C<sub>60</sub> heterojunction, commonly used in organic photovoltaics, via heterodyne-detected
time-resolved second-harmonic generation. We compare these results
to theoretical predictions based on a Fermi’s golden rule approach,
with input parameters obtained using first-principles calculations
for two different equilibrium geometries of a molecular donor–acceptor
in a dielectric continuum model. The calculated rates (∼2 ps<sup>–1</sup>) overestimate the measured rates (∼0.1 ps<sup>–1</sup>), which is consistent with the expectation that the
calculated rates represent an upper bound over the experimental ones.
The comparison provides valuable understanding of how the structure
of the electron donor–acceptor interface affects the CT kinetics
in organic photovoltaic systems