Hindawi Publishing Corporation ISRN Electronics Volume 2013, Article ID 652587, 6 pages http://dx.doi.org/10.1155/2013/652587 Research Article Modeling of Electronic Transport through Metal/Polymer Interfaces in Thin Film Transistors S. Alborghetti and P. Stamenov School of Physics and CRANN, Trinity College Dublin, Dublin 2, Ireland Correspondence should be addressed to S. Alborghetti; alborgs@tcd.ie Received 29 November 2012; Accepted 16 January 2013 Academic Editors: R. Luzzi, L.-F. Mao, Y. Takahashi, P. Wachulak, and Y.-H. Wang Copyright © 2013 S. Alborghetti and P. Stamenov. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We report on the modeling of electrical characteristics and contact-related efects of organic thin flm 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 ofen observed in these devices. Te 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. Te 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 feld 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 fexible devices for logic circuits, matrix displays, and photovoltaic cells. A common trait of polymer- based devices is that their performances critically depend on the efciency with which charge carriers move within the conjugated material. Research eforts have been devoted to the development of high mobility polymers. Maximum mobilities of order 0.1 cm 2 V −1 s −1 are found in thin flms of polythiophene derivatives having enhanced interchain ordering [1]. Tis is about 4 orders of magnitude smaller than crystalline silicon, but similar to amorphous silicon. Te low mobilities will naturally restrict applications to low frequency electronics. Te 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 feld efect transistors (FETs), this is motivated by the necessity to obtain switching speeds and drive currents that meet the requests of applica- tions. In these circumstances the contact efects are expected to heavily afect the performance of the devices. In transistors, the drain currents scales with the transistor width, as the actual contact resistance   is inversely proportional to the channel width (  ∝ −1 ). Terefore, it is convenient to use the product of contact resistance and channel width,   =  , as a measure of the contact resistance. Contact resistance at a metal-organic interface is usually detected to be in the range of 10 kΩ cm–10 MΩ cm [2, 3]. In inorganic devices; for example, in FETs, source and drain contacts are typically optimized by selective semiconductor doping, which leads to much lower values, and so it is expected that