We report on the modeling of electrical characteristics and contact-related effects of organic thin film transistors. An equivalent circuit is employed to simulate the electrical behavior of the devices. We suggest that, at low temperature, tunneling is the dominant mechanism of charge carrier injection, originating the nonlinearities often observed in these devices. The temperature dependence of the output characteristics is due to the fraction of carriers that are injected, via the competing mechanism of thermal activation, above the interface energy barrier at metal/organic contacts. The model successfully reproduces the electrical characteristics of P3HT polymeric transistors and allows for the decoupling and the study of the temperature dependence of the charge conduction through the organic channel. 1. Introduction Research into solution processable organic electronics has been a vibrant field of research over the last three decades. Many studies have focused on the realization of devices made with conjugated polymers due to the availability of simple deposition techniques to process these materials. While not destined to replace silicon-based technologies, they promise the advent of fully flexible devices for logic circuits, matrix displays, and photovoltaic cells. A common trait of polymer-based devices is that their performances critically depend on the efficiency with which charge carriers move within the conjugated material. Research efforts have been devoted to the development of high mobility polymers. Maximum mobilities of order 0.1？cm2V？1s？1 are found in thin films of polythiophene derivatives having enhanced interchain ordering [1]. This is about 4 orders of magnitude smaller than crystalline silicon, but similar to amorphous silicon. The low mobilities will naturally restrict applications to low frequency electronics. The problem of contact resistance in hybrid organic devices has recently been recognized as a major issue too. At the earlier stages of research in this area, the conductivity of the available media has been low, so that the device output current has in most cases been entirely limited by the organic channel resistance. As new materials with improved mobility have been synthetized, limitations by contact resistance are getting more and more crucial. Reinforcing this concern, modern devices are typically designed with much shorter channel length. As an example, in field effect transistors (FETs), this is motivated by the necessity to obtain switching speeds and drive currents that meet the requests of applications. In these
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