Magnetic Field Effect on Photocarriers in an Organic Film Studied by Simultaneous Optical and Electrical Detection

Magnetic field effects (MFEs) on the electric conductance in organic semiconductor films provide valuable information regarding the carrier dynamics. There have been reported two major mechanisms for the MFE; one is due to electron–hole pair recombination, and the other is due to bipolaron formation from two carriers of the same charge. Although the former and latter effects appear on the concentration and drift mobility of the charges, respectively, the observed MFEs on the conductance are similar. For a clearer assignment of the MFE mechanism, we have utilized simultaneous optical and electrical detection of the time-dependent MFE on the photocarriers in a P3HT:PCBM bulk heterojunction film. The optical signal proportional to the concentration and the electrical signal proportional to the concentration and the mobility exhibit similar MFEs, which demonstrate that the electron–hole pair mechanism is dominant in the present film.