Revealing Spin-Orbit Coupling Effects in π-Conjugated Polymers by Multifrequency Electrically Detected Magnetic Resonance

Charge carriers in organic semiconductors typically have weak spin-orbit coupling (SOC), however, for some magneto-opto-electronic materials properties, SOC is non-negligible. To investigate charge carrier SOC effects in π-conjugated polymer thin films, we carried out electrically detected magnetic resonance (EDMR) spectroscopy on bipolar injection devices made of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), the related poly-phenylenevinylene SY-PPV, polyfluorene (PFO) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) over a broad magnetic field range [1]. We observed strong broadening of the charge carrier EDMR lines with increasing magnetic field, reflecting the increasing influence of SOC induced g-factor distributions. The analysis of this broadening allowed to test theoretical density functional theory predictions of charge carrier wave functions and an assignment of electrons and holes to the different observed lines. Furthermore, access to these g-factor distributions also allows for predictions of the magneto-resistance characteristics of the studied materials. [1] G. Joshi et al., Appl. Phys. Lett. 109, 103303 (2016).