Electron spin resonance measurements of iodine-doped pentacene films

Pentacene films, grown on polyethylene terephthalate (PET) substrates, were doped with iodine. Electron spin resonance (ESR) measurements were made for the films in the temperature range of 100-300 K. Two regimes of doping stages were discernible: a light (intercalation) doping regime and a heavy (saturation) doping regime. The light doping regime was concluded to be dominated by localized holes that were trapped at low temperatures, which indicated trap states near the valence band edge. The heavy doping regime was dominated by different localized spins following Curie behavior. The temperature-dependence of the ESR linewidths and g-values also reflected the two doping regimes.