Abstract
The unique properties of organic semiconductors make them versatile base materials for many
applications ranging from light emitting diodes to transistors. The low spin-orbit coupling typical
for carbon-based materials and the resulting long spin lifetimes give rise to a large in
uence of the
electron spin on charge transport which can be exploited in spintronic devices or to improve solar
cell eciencies. Magnetic resonance techniques are particularly helpful to elucidate the microscopic
structure of paramagnetic states in semiconductors as well as the transport processes they are
involved in. However, in organic devices the nature of the dominant spin-dependent processes is
still subject to considerable debate. Using multi-frequency pulsed electrically detected magnetic
resonance (pEDMR), we show that the spin-dependent response of P3HT/PCBM solar cells at low
temperatures is governed by bipolar polaron pair recombination involving the positive and negative
polarons in P3HT and PCBM, respectively, thus excluding a unipolar bipolaron formation as the
main contribution to the spin-dependent charge transfer in this temperature regime. Moreover the
polaron-polaron coupling strength and the recombination times of polaron pairs with parallel and
antiparallel spins are determined. Our results demonstrate that the pEDMR pulse sequences recently
developed for inorganic semiconductor devices can very successfully be transferred to the study of
spin and charge transport in organic semiconductors, in particular when the dierent polarons can
be distinguished spectrally.
Original language | English |
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Article number | arXiv:1505.01411v1 |
Journal | arXiv |
Number of pages | 8 |
Publication status | Published - 2015 |