Magnetic Resonance Characteristics of Negative Polarons in Neat Poly(3-hexyl-thiophene)

Magnetic resonance characteristics of carriers of both electron spin and electric charge (polarons) in conjugated polymers are required for a deeper understanding of properties of these semiconducting materials. In poly(3-hexyl-thiophene), P3HT, which is an important material for photovoltaic applications, such information is available only for positive polarons, which are readily generated in the presence of electron acceptors via photoinduced processes. Influence of an external magnetic field on X-ray-induced delayed fluorescence from undoped P3HT and its solutions allowed us to visualize the spin interactions in the primary polaron pairs and to estimate the g-tensor components (g_⊥ ≈ 2.0023, g_|| ≈ 2.008) for the negative charge carriers in P3HT molecules. There is evidence that in neat regioregular P3HT, the g-tensor anisotropy for the polarons, migrating along polymer chains, is averaged partially because of irregularities in the polymer structure.