title: Magnetic field effects of photocarrier generation in bulk heterojunctions at low temperature.
abstract: We report an experimental investigation of the magnetic field effect (MFE) in polymer bulk heterojunction devices at temperatures below 10 K using photocarrier extraction by linearly increasing voltages. The examined devices were composed of an active layer of poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester. In the experiments, the delay time (td) dependence of the MFE was investigated in detail. For td< 80 μs, a positive MFE was observed in the field region B < 0.1 T and a negative MFE was observed for B > 0.2 T. For td> 8 ms, only a positive MFE proportional to B2was observed. For the photocurrent pulse detected immediately after light irradiation, the MFE was negligibly small. In a high magnetic field of 15 T, a significant MFE exceeding 80% was observed at 1.8 K for td= 800 ms. We discuss the results based on a model of triplet-singlet (or singlet-triplet) conversion in the magnetic field and estimate the exchange integral for the charge-transfer exciton in this photovoltaic cell.
authors.affiliation: Graduate School of Material Science, University of Hyogo, 3-2-1 Kohto, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan. tajima@sci.u-hyogo.ac.jp.
authors.forename: H
authors.initials: H
authors.lastname: Tajima
authors.forename: Y
authors.initials: Y
authors.lastname: Nishioka
authors.forename: S
authors.initials: S
authors.lastname: Sato
authors.forename: T
authors.initials: T
authors.lastname: Suzuki
authors.forename: M
authors.initials: M
authors.lastname: Kimata