1 research outputs found
Femtosecond Dynamics of Photoexcited C<sub>60</sub> Films
The well known organic
semiconductor C<sub>60</sub> is attracting
renewed attention due to its centimeter-long electron diffusion length
and high performance of solar cells containing 95% fullerene, yet
its photophysical properties remain poorly understood. We elucidate
the dynamics of Frenkel and intermolecular (inter-C<sub>60</sub>)
charge-transfer (CT) excitons in neat and diluted C<sub>60</sub> films
from high-quality femtosecond transient absorption (TA) measurements
performed at low fluences and free from oxygen or pump-induced photodimerization.
We find from preferential excitation of either species that the CT
excitons give rise to a strong electro-absorption (EA) signal but
are extremely short-lived. The Frenkel exciton relaxation and triplet
yield strongly depend on the C<sub>60</sub> aggregation. Finally,
TA measurements on full devices with applied electric field allow
us to optically monitor the dissociation of CT excitons into free
charges for the first time and to demonstrate the influence of cluster
size on the spectral signature of the C<sub>60</sub> anion