A simple and robust approach to reducing contact resistance in organic transistors

Katrina J Barth,John E Anthony,Lee J Richter,Hu Chen,Zachary A Lamport,Eliot Gann,Oana D Jurchescu,Sebastian Engmann,Martin Guthold,Dean M Delongchamp,Iain Mcculloch,Hyunsu Lee

doi:10.1038/s41467-018-07388-3

Abstract

Efficient injection of charge carriers from the contacts into the semiconductor layer is crucial for achieving high-performance organic devices. The potential drop necessary to accomplish this process yields a resistance associated with the contacts, namely the contact resistance. A large contact resistance can limit the operation of devices and even lead to inaccuracies in the extraction of the device parameters. Here, we demonstrate a simple and efficient strategy for reducing the contact resistance in organic thin-film transistors by more than an order of magnitude by creating high work function domains at the surface of the injecting electrodes to promote channels of enhanced injection. We find that the method is effective for both organic small molecule and polymer semiconductors, where we achieved a contact resistance as low as 200 Ωcm and device charge carrier mobilities as high as 20 cm2V−1s−1, independent of the applied gate voltage.

Highlights

Efficient injection of charge carriers from the contacts into the semiconductor layer is crucial for achieving high-performance organic devices
In organic field-effect transistors (OFETs), this issue becomes more severe as the channel dimensions are minimized, since the channel resistance decreases with shrinking channel length, while the contact resistance is independent of this variable
A summary of on/off ratios obtained in diF-TES ADT OFETs fabricated on source drain contacts deposited at a rate of 0.5 Ås−1 is displayed in Supplementary Fig. 2

Summary

Introduction

Efficient injection of charge carriers from the contacts into the semiconductor layer is crucial for achieving high-performance organic devices. The development of new materials hinges on a correct evaluation of mobility: the equations adopted from silicon-based metal-oxide semiconductor field-effect transistors (MOSFETs) for the characterization of OFET operation assume negligible contact resistance, and they fail when the devices are severely limited by contacts. In this case, it is impossible to access the intrinsic properties of materials and to provide meaningful feedback for material design[10,11,12,13]. Evaluation of the SAM/Au surfaces using scanning Kelvin probe microscopy (SKPM) indicated that there exist local enhancement regions in the work function of the electrodes fabricated using a low deposition rate, pointing to the existence of regions with more efficient charge injection due to enhanced SAM order, a feature which is absent in the samples obtained via fast metal deposition

Methods

Results

Conclusion