Significant Performance Improvement in n‐Channel Organic Field‐Effect Transistors with C<sub>60</sub>:C<sub>70</sub> Co‐Crystals Induced by Poly(2‐ethyl‐2‐oxazoline) Nanodots
Sungho Nam, Dongyoon Khim, Gerardo Martínez, Aakash Varambhia, Peter D. Nellist, Youngkyoo Kim, Thomas D. Anthopoulos, Donal D. C. Bradley
Abstract
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 (C 60 ‐I h )[5,6]fullerene (C 60 ) and (C 70 ‐D 5h(6) )[5,6]fullerene (C 70 ) blend films, with an increase from 0.1 to 2.1 cm 2 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 C 60 :C 70 co‐crystal structure within the blend films.