Hydrostatic pressure dependence of charge carrier transport in single-crystal rubrene devices

Abstract

Hydrostatic pressure was applied to single-crystal rubrene photoconductors and p channel field-effect transistors. Under illumination from a GaInN light-emitting diode, we observed linear increases in photoconductivity, by up to a factor of 2.1 at 0.43 GPa. We also measured increases in the drain current of the single-crystal rubrene organic field-effect transistors (OFETs) with increasing pressure up to 0.52 GPa. Analyzing the transfer characteristics of the OFETs, we extracted the pressure dependence of the field-effect hole mobility. The different OFETs examined showed similar hole mobility increase ratios with pressure, although their atmospheric pressure mobilities varied by more than a factor of two. Threshold voltages shifts with pressure were small. All results were reversible, i.e., the measured currents returned to their atmospheric pressure values upon release of pressure unless complete device failure occurred at the highest pressure.

Charge Transport in Organic and Polymeric Semiconductors for Flexible and Stretchable Devices

“…By applying an in-plane, uniaxial, global compressive strain, 1D wrinkling across the conducting channel was induced (Figure 3 a, bottom of a(ii)). Similar to that presented in previous reports, [84][85][86] mechanical compression reduced the intermolecular distances, resulting in an increase of mobility, while tension increased the intermolecular distances, decreasing mobility. However, in this wrinkling OSCFET system, the difference is that mechanical compression and tension are coexistent and inhomogeneous.…”

“…[84][85][86][87] Meanwhile, in some unique cases, irreversible strain-dependant behavior with device degradation under strain is also found. [ 92 ] In the latter report, the authors think that the electromechanical property of OTFTs is signifi cantly dominated by the molecular structures used in the active layer, and independent from the underlying dielectric layer.…”

“…[ 84 ] Similar increases of carrier mobility and or photoconductivity have also been demonstrated by other groups, in tetracene, pentacene, and rubrene single crystals, on undergoing deformation by bending on fl exible substrates or under hydrostatic pressure, giving compressed intermolecular distances. [ 85,86 ] Recently, Briseno and co-workers carried out a more in-depth investigation of the strain effect on charge transport based on rubrene-OSCFETs. [ 87 ] In this system, a nondestructive, reversible, and predictable strain was introduced on the rubrene crystal through a unique device confi guration, where the rubrene OSCFET was fabricated on a cylindrical elastomeric substrate (Figure 3 a, top of a(ii)).…”

Theory of Charge Transport in Carbon Electronic Materials

“…Since the molecular parameters enter explicitly into evaluation of the charge diffusion coefficient, this approach can be used for molecular design toward high charge mobility. In this picture, it is found that the dynamic disorder is very much dependent on the space dimension, and sometimes, it leads to the phonon-assisted current, namely, dynamic disorder enhances the charge mobility [26]. Applications have been performed to a variety of molecular materials, e.g., siloles [20], triphenylamines [21,22], oligothiophenes [24], and oligoacenes [25,26].…”

“…In the first category, the electron interacts strongly with intramolecular vibrations, namely, the intermolecular electron coupling is much less than the molecular reorganization energy. In this case, the electron is fully self-localized, i.e., each molecule acts as a trap, and the charge transport can be viewed as an intermolecular hopping process [11,[20][21][22][23][24][25][26]. It is appropriate to apply the Marcus theory to calculate the intermolecular charge transfer rates, and a more elaborate and appropriate description is to incorporate nuclear tunneling effects to account the quantum nature of molecular vibration, which we found is essential since the intramolecular vibration is generally of high frequency, invalidating the classical charge transfer theory [25].…”