Parasitic contact resistance effects are becoming a major issue in organic transistors in that they can severely limit or even dominate their overall transistor performance. We present a systematic study of the contact resistance in bottom-contact polymer field-effect transistors made from poly(3-hexylthiophene) (P3HT) as well as poly-9,9′dioctyl-fluorene-co-bithiophene (F8T2). A microscopic approach based on noncontact scanning-probe potentiometry was used to directly separate the transport properties of the transistor channel and the electrode/polymer contacts, giving very accurate experimental access to both the source and drain contact resistance. The influence of the relevant parameters (temperature, electrode work function, ionization potential of the polymer, charge carrier mobility) on the source/drain contact resistance is investigated. We find that for “good” source/drain contacts that give rise to relatively small overall contact resistances (⩽50 kΩ cm), e.g., P3HT with chromium–gold electrodes, the source and the drain contact resistances are almost identical and are governed by bulk transport through the conjugated polymer. However, for “bad” contacts with a Schottky barrier for hole injection φb⩾0.3 eV, e.g., F8T2 with gold electrodes, the source contact resistance is considerably larger than the drain contact resistance and is dominated by charge-carrier injection at the source. Surprisingly small activation energies of 60–140 meV have been found for the source contact resistance, which are smaller than both φb and the activation energy of the mobility. From this we conclude that the commonly assumed (diffusion-limited) thermionic-emission models do not adequately describe the charge injection process in bottom-contact polymer transistors. On the basis of our results we propose a simple model, in which the source contact resistance is assumed to be the sum of resistance arising from the injection process and resistance due to bulk transport through a depletion region, whereas only the latter contributes to the drain contact resistance.

The fine balancing of the lateral intermolecular interactions and the bonding to the substrate enables the self‐assembly of supramolecular nanostructures at surfaces to be achieved. The scanning tunneling microscopy image shows the formation of a twin chain of 4‐[trans‐2‐(pyrid‐4‐yl)vinyl]benzoic acid deposited on an Ag(111) surface in ultra‐high vacuum.

Over the last decade the performance of organic field-effect transistors (FETs) has seen a remarkable improvement, owing to advances in material development as well as device optimization. Field-effect mobilities on the order of 10 cm 2 V À1

We report on high-resolution potentiometry of operating organic thin-film field-effect transistors by means of scanning Kelvin probe force microscopy. It is demonstrated that the measured potential reflects the electrostatic potential of the accumulation layer at the semiconductor/insulator interface. We present data revealing gate bias and lateral electric field dependence of the field-effect mobility in poly(hexylthiophene) at temperatures from 50 to 300 K.

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