The Hall effect and an increase of field-effect mobility with decreasing temperature is observerd in n-channel single-crystal organic field-effect transistors (OFETs). A quantitative analysis of these findings, together with results on different p-channel transistors, indicate the importance of the semiconductor molecular polarizability and the structure of the charge transport layers in the crystal for the observation of band-like transport in OFETs.

Organic semiconductors based on small conjugated molecules generally behave as insulators when undoped, but the heterointerfaces of two such materials can show electrical conductivity as large as in a metal. Although charge transfer is commonly invoked to explain the phenomenon, the details of the process and the nature of the interfacial charge carriers remain largely unexplored. Here we use Schottky-gated heterostructures to probe the conducting layer at the interface between rubrene and PDIF-CN(2) single crystals. Gate-modulated conductivity measurements demonstrate that interfacial transport is due to electrons, whose mobility exhibits band-like behaviour from room temperature to ~150 K, and remains as high as ~1 cm(2) V(-1) s(-1) at 30 K for the best devices. The electron density decreases linearly with decreasing temperature, an observation that can be explained quantitatively on the basis of the heterostructure band diagram. These results elucidate the electronic structure of rubrene/PDIF-CN(2) interfaces and show the potential of Schottky-gated organic heterostructures for the investigation of transport in molecular semiconductors.

In organic field-effect transistors, the structure of the constituent molecules can be tailored to minimize the disorder experienced by charge carriers. Experiments on two perylene derivatives show that disorder can be suppressed by attaching longer core substituents - thereby reducing potential fluctuations in the transistor channel and increasing the mobility in the activated regime - without altering the intrinsic transport properties.

We investigated transport properties of organic heterointerfaces formed by single-crystals of two organic donor-acceptor molecules, tetramethyltetraselenafulvalene and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Whereas the individual crystals have unmeasurably high resistance, the interface exhibits a resistivity of few tens of megohm with a temperature dependence characteristic of a small gap semiconductor. We analyze the transport properties based on a simple band diagram that naturally accounts for our observations in terms of charge transfer between two crystals. Together with the recently discovered tetrathiafulvalene–TCNQ interfaces, these results indicate that single-crystal organic heterostructures create functional electronic systems with properties relevant to both fundamental and applied fields

High-performance n-type organic field-effect transistors were developed with ionic-liquid gates and N,N′′-bis(n-alkyl)-(1,7 and 1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide)s single-crystals. Transport measurements show that these devices reproducibly operate in ambient atmosphere with negligible gate threshold voltage and mobility values as high as 5.0 cm2/V s. These mobility values are essentially identical to those measured in the same devices without the ionic liquid, using vacuum or air as the gate dielectric. Our results indicate that the ionic-liquid and n-type organic semiconductor interfaces are suitable to realize high-quality n-type organic transistors operating at small gate voltage, without sacrificing electron mobility