Charge Transport in High-Quality Crystals of Molecular Semiconductors
Abstract
Field-effect transistors based on polyacenes and oligothiophenes have reached performances similar to a-Si:H devices and low switching voltages, a high degree of integration, and all-solution-processed thin film devices have been demonstrated, yet the knowledge about the microscopic charge transport is quite limited. In order to study intrinsic material properties we grew high-quality single crystals from the vapor phase. We determined the charge carrier mobility in these materials by the space charge limited current technique, by field-effect transistor measurements, and by the photo-Hall-effect. The mobility obeys a power-law dependence on temperature reaching values as high as 1000 cm^2/Vs at low temperatures indicating band-like charge transport in delocalized levels. The rather strong electric field dependence can be described by acoustic phonon scattering. Furthermore, at low temperatures and high electric fields hot carrier velocity saturation is observed. Band transport changes over to hopping motion due to carrier localization when the effective bandwidth shrinks, i.e. at high temperatures (sexithiophene), in doped samples due to increased intermolecular distances (pentacene), or in a crystallographic direction of small molecular overlap (oligothiophenes). As a result of these studies performance limits for organic field-effect devices based on polyacenes and oligothiophenes can be estimated. Furthermore, the understanding of the band-like charge transport and electron-phonon interaction might lead to the design of new materials with better performances. * In collaboration with Ch. Kloc, S. Berg, G. A. Thomas, and B. Batlogg
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2000
- Bibcode:
- 2000APS..MARI21004S