Low temperature electron paramagnetic resonance studies and spin susceptibility of phosphorus-implanted C60 films for solar cells

Low temperature electron paramagnetic resonance (EPR) measurements have been made to clarify the origin and nature of paramagnetic electronic states responsible for the observed EPR signal in P+-implanted C60 films. The data collected from the temperature dependence of the EPR signal intensity and the spin susceptibility revealed that the unpaired spin fellows the Curie law at T < 20 K, while a clear deviation was observed at about T > 20 K. The temperature dependence of the linewidths indicates that the spin mobility occurs by hopping motion. In addition, the relation among defects, electrical, and optical properties was detected and analyzed. Finally, this study suggests that the transport mechanism occurs by hopping motion and the unpaired spins are partially localized.