Magnetic Field\nEffect on Photocarriers in an Organic\nFilm Studied by Simultaneous Optical and Electrical Detection

Magnetic\nfield effects (MFEs) on the electric conductance in organic\nsemiconductor films provide valuable information regarding the carrier\ndynamics. There have been reported two major mechanisms for the MFE;\none is due to electron–hole pair recombination, and the other\nis due to bipolaron formation from two carriers of the same charge.\nAlthough the former and latter effects appear on the concentration\nand drift mobility of the charges, respectively, the observed MFEs\non the conductance are similar. For a clearer assignment of the MFE\nmechanism, we have utilized simultaneous optical and electrical detection\nof the time-dependent MFE on the photocarriers in a P3HT:PCBM bulk\nheterojunction film. The optical signal proportional to the concentration\nand the electrical signal proportional to the concentration and the\nmobility exhibit similar MFEs, which demonstrate that the electron–hole\npair mechanism is dominant in the present film.