Wednesday CPP 24 : Organic Semiconductors

The contact resistance is known to severely hamper the performance of organic thin-film transistors. This is particular true when dealing with large injection barriers, high mobility organic semiconductors, or short channel lengths. A common assumption is that the primary quantity determining the value of the contact resistance is the injection barrier at the source electrode. Using drift-diffusion based simulations we show that in sharp contrast to this assumption also the actual device geometry (topvs. bottom contact), the mobility of the used active material as well as the operation condition of the device can change the contact resistance by several orders of magnitude.[1] The final value of the contact resistance arises from a subtle interplay of all these factors as it is crucially determined by local fields and carrier densities. We also find that the dominant mode of injection (thermionic vs. tunneling) is strongly affected by the above parameters and that (in analogy with the findings of Brondijk et al. [2]) the inclusion of barrier shaping fields, mirror charge effects and recombination at the electrode surfaces [3] is essential to obtain qualitatively meaningful results. [1] Adv. Funct. Mater., prov. accepted, [2] Org. El. 13, 1526 (2012); [3] Org. El. 13, 1887 (2012)