The influence of light-induced paramagnetic states on the photocurrent
generated by polymer:fullerene solar cells is studied using spin-sensitive
techniques in combination with laser-flash excitation. For this purpose, we
developed a setup that allows for simultaneous detection of transient electron
paramagnetic resonance as well as transient electrically detected magnetic
resonance (trEDMR) signals from fully processed and encapsulated solar cells.
Combining both techniques provides a direct link between photoinduced triplet
excitons, charge transfer states, and free charge carriers as well as their
influence on the photocurrent generated by organic photovoltaic devices. Our
results obtained from solar cells based on poly(3-hexylthiophene) as electron
donor and a fullerene-based electron acceptor show that the resonant signals
observed in low-temperature (T = 80 K) trEDMR spectra can be attributed to
positive polarons in the polymer as well as negative polarons in the fullerene
phase, indicating that both centers are involved in spin-dependent processes
that directly influence the photocurrent
