Magnetic field effect on photocurrent in N,N'-di(naphthalene-l-yl)-N,N'- diphenyl-benzidine (NPB)

We studied organic magnetoresistance (OMAR) and magneto-photocurrent (MPC) in ITO/N,N'-di(naphthalene-l-yl)-N,N'-diplienyl-benzidine (NPB)/A1 sandwich devices with NPB thicknesses of 50 nm. Without illumination, no OMAR is observable. While the MPC curves are found to have different line shapes containing a low field and a high field component, depending on excitation photon energy and applied bias. The analysis of experimental results indicate that: (i) the magnetic field effects in NPB is associated with excitonic states, and (ii) the dissociation of singlet excitons is associated to the high field component and triplet-exciton-charge interaction is to the low field component in MPC curves.