Angular-Dependent EDMR Linewidth for Spin-Dependent Space-Charge-Limited Conduction in a Polycrystalline Pentacene

Abstract

Spin-dependent space-charge-limited carrier conduction in a Schottky barrier diode using polycrystalline p-type π-conjugated molecular pentacene is explored using multiple-frequency electrically detected magnetic resonance (EDMR) spectroscopy with a variable-angle configuration. The measured EDMR spectra are decomposed into two components derived, respectively, from mobile and trapped positive polarons. The linewidth of the EDMR signal for the trapped polarons increases with increasing resonance magnetic field for an in-plane configuration where the normal vector of the device substrate is perpendicular to the resonance magnetic field, while it is independent of the field for an out-of-plane configuration. This difference is consistent with the pentacene arrangement on the device substrate, where pentacene molecules exhibit a uniaxial orientation on the out-of-substrate plane. By contrast, the mobile polarons do not show anisotropic behavior with respect to the resonance magnetic field, indicating that the anisotropic effect is averaged out owing to carrier motion. These results suggest that the orientational arrangements of polycrystalline pentacene molecules in a nano thin film play a crucial role in spin-dependent electrical conduction.

Electrically Detected Magnetic Resonance Observations of Spin‐Dependent Space‐Charge‐Limited Conduction in Regioregular Poly(3‐Hexylthiophene)

“…Finally, we consider the influence of the differences in the orientation of RR‐P3HT on the substrate on the EDMR spectrum. In our previous studies of a pentacene Schottky barrier diode, anisotropic behavior was observed in the linewidth of the EDMR signal, which depended on the direction of the external static magnetic field with respect to oriented pentacene molecules on the substrate . However, almost no difference in linewidth was found between the CF device element with face‐on stacking and the DCB and DCB‐W elements with edge‐on stacking.…”

Molecular Semiconductors for Logic Operations: Dead‐End or Bright Future?

“…His group also observed the Hall effect in single‐crystals and polycrystalline thin films of DNTT 9 ( R = H) and pentacene 1 , explaining the rationale behind the difference in charge carrier densities achieved through the Hall effect and the gating. Room temperature devices of DNTT 9 ( R = H) present a coherence factor of 1, while the ones of pentacene 1 (<1 at room temperature) require a decrease of temperature/increase of pressure to reach a value close to unity, as result of the stronger impact of dynamic disorder within the system (localized and delocalized contribution to the transport) . Sirringhaus et al observed a similar effect in solution processed devices of TIPS‐PEN 4 and diF‐TES‐ADT 5a .…”

“…Requiring a similar setup to the one used for OFET's characterization, the method has reproducibly confirmed mobility values of some of the best p‐ and n‐type materials. In the quest for understanding the charge transport mechanisms taking place in organic semiconductors, OFETs have been used to study the impact of temperature and pressure on mobility, leading to the observation of increased values at lower temperature and higher pressure/strain, result of reduced dynamic disorder . The highest reproducibly attained mobility has been achieved by Frisbie et al on deuterated rubrene vacuum gap single‐crystal OFETs, hitting a strikingly high 45 cm 2 V −1 s −1 below 100K .…”