On the Role of Contact Resistance and Electrode Modification in Organic Electrochemical Transistors

• Published in: Advanced materials (Weinheim) 2019-09, Vol.31 (37), p.e1902291-n/a
• Main Authors: Paterson, Alexandra F., Faber, Hendrik, Savva, Achilleas, Nikiforidis, Georgios, Gedda, Murali, Hidalgo, Tania C., Chen, Xingxing, McCulloch, Iain, Anthopoulos, Thomas D., Inal, Sahika
• Format: Article
• Language: English
• Subjects: Contact resistance; electrode modification; Electrodes; Electronics; Gold; Investigations; Morphology; morphology/organic semiconductors; organic electrochemical transistors; self‐assembled monolayers; Semiconductor devices; Surface energy; Transconductance; Transistors; Wetting
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201902291

Contact resistance is renowned for its unfavorable impact on transistor performance. Despite its notoriety, the nature of contact resistance in organic electrochemical transistors (OECTs) remains unclear. Here, by investigating the role of contact resistance in n‐type OECTs, the first demonstration of source/drain‐electrode surface modification for achieving state‐of‐the‐art n‐type OECTs is reported. Specifically, thiol‐based self‐assembled monolayers (SAMs), 4‐methylbenzenethiol (MBT) and pentafluorobenzenethiol (PFBT), are used to investigate contact resistance in n‐type accumulation‐mode OECTs made from the hydrophilic copolymer P‐90, where the deliberate functionalization of the gold source/drain electrodes decreases and increases the energetic mismatch at the electrode/semiconductor interface, respectively. Although MBT treatment is found to increase the transconductance three‐fold, contact resistance is not found to be the dominant factor governing OECT performance. Additional morphology and surface energy investigations show that increased performance comes from SAM‐enhanced source/drain electrode surface energy, which improves wetting, semiconductor/metal interface quality, and semiconductor morphology at the electrode and channel. Overall, contact resistance in n‐type OECTs is investigated, whilst identifying source/drain electrode treatment as a useful device engineering strategy for achieving state of the art n‐type OECTs. Contact resistance (RC) is renowned for its unfavorable yet significant impact on transistor performance, especially for n‐type polymers. The impact of RC on accumulation‐mode, n‐type organic electrochemical transistors (OECTs) is investigated by modifying the energetic mismatch at the metal/semiconductor interface using self‐assembled monolayers. This interface modification is a useful device engineering strategy for achieving high‐performance n‐type OECTs.