Significant Performance Improvement in n-Channel Organic Field-Effect Transistors with C60 :C70 Co-Crystals Induced by Poly(2-ethyl-2-oxazoline) Nanodots

Sungho Nam; Dongyoon Khim; Gerardo T Martinez; Aakash Varambhia; Peter D Nellist; Youngkyoo Kim; Thomas D Anthopoulos; Donal D C Bradley

doi:10.1002/adma.202100421

Significant Performance Improvement in n-Channel Organic Field-Effect Transistors with C₆₀ :C₇₀ Co-Crystals Induced by Poly(2-ethyl-2-oxazoline) Nanodots

Adv Mater. 2021 Aug;33(31):e2100421. doi: 10.1002/adma.202100421. Epub 2021 Jun 24.

Authors

Sungho Nam¹, Dongyoon Khim², Gerardo T Martinez³, Aakash Varambhia³, Peter D Nellist³, Youngkyoo Kim⁴, Thomas D Anthopoulos⁵, Donal D C Bradley^{1

5}

Affiliations

¹ Department of Physics, University of Oxford, Oxford, OX1 3PD, UK.
² Blackett Laboratory, Department of Physics and Centre for Plastic Electronics, Imperial College London, London, SW7 2BW, UK.
³ Department of Materials, University of Oxford, Oxford, OX1 3PH, UK.
⁴ Organic Nanoelectronics Laboratory and KNU Institute for Nanophotonics Applications (KINPA), School of Applied Chemical Engineering, Kyungpook National University, Daegu, 41566, Republic of Korea.
⁵ Physical Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia.

PMID: 34165833
DOI: 10.1002/adma.202100421

Abstract

Solution-processed organic field-effect transistors (OFETs) have attracted great interest due to their potential as logic devices for bendable and flexible electronics. In relation to n-channel structures, soluble fullerene semiconductors have been widely studied. However, they have not yet met the essential requirements for commercialization, primarily because of low charge carrier mobility, immature large-scale fabrication processes, and insufficient long-term operational stability. Interfacial engineering of the carrier-injecting source/drain (S/D) electrodes has been proposed as an effective approach to improve charge injection, leading also to overall improved device characteristics. Here, it is demonstrated that a non-conjugated neutral dipolar polymer, poly(2-ethyl-2-oxazoline) (PEOz), formed as a nanodot structure on the S/D electrodes, enhances electron mobility in n-channel OFETs using a range of soluble fullerenes. Overall performance is especially notable for (C₆₀ -I_h )[5,6]fullerene (C₆₀ ) and (C₇₀ -D_5h(6) )[5,6]fullerene (C₇₀ ) blend films, with an increase from 0.1 to 2.1 cm² V^-1 s^-1 . The high relative mobility and eighteen-fold improvement are attributed not only to the anticipated reduction in S/D electrode work function but also to the beneficial effects of PEOz on the formation of a face-centered-cubic C₆₀ :C₇₀ co-crystal structure within the blend films.

Keywords: C60:C70 co-crystals; n-channel organic field-effect transistors; nanodot layers; poly(2-ethyl-2-oxazoline).