Corona Poling Induced Phase Transition to Highly Polar Phase in P(VDF-TrFE-CFE) Dielectric and Charge Transport of Organic Field-Effect Transistors

Abstract

Increasing the number of charge carriers flowing through the charge transport channel to improve the electrical performance of organic field-effect transistors (OFETs) is important because it leads to a low driving voltage and a high drain current value. This paper proposes a new strategy, the corona poling process, to enhance the electrical performance of OFETs using an external electric field when forming a dielectric film using a PVDF-based high-k dielectric terpolymer, P(VDF-TrFE-CFE). A corona poling process was applied to align the dipoles with high-k dielectric molecules and improve the capacitance, thereby increasing the number of charge carriers. Through this process, by observing the phase transition of a PVDF dielectric through a corona poling process in the GIWAXS data, the phase transition through an external electric field was thoroughly revealed for the first time. As a result, the capacitance of high-k dielectric films can be improved, and the amount of charge carriers can be increased by a simple corona poling process. In addition, to reduce the effect of deep trap sites caused by the dipole alignment, a thin low-k dielectric, polystyrene (PS), was introduced between the active and high-k dielectric layers to provide trap site passivation, thereby increasing the electrical performance of the OFET. Therefore, through this strategy, using a diketopyrrolopyrrole (DPP)-based donor−acceptor (D−A) copolymer as an active material of OFET, the average saturation region hole mobility was improved from 0.34 to 0.60 cm 2 /Vs. Thus, the electrical performances of the OFETs were improved by enhancing the capacitance through the corona poling process and reducing the charge carrier trap sites introduced by the high-k and low-k bi-layer dielectric layer. Importantly, this work offers a new strategy for the post-treatment to improve electrical performance of organic devices.

External electric field treatment for improving the morphology and electrical performance of P(NDI2OD-T2)

“…33–41 Among many external fields, the application of an external electric field (EEF) to films enables realizing precise directionality control through molecular dipole alignment. 33,42–49 Additionally, since all organic materials have local dipole moments and polarizability, EEF treatment, a process that induces the alignment of dipoles, can be effectively and broadly applied without any restrictions on any target material and, therefore, can be applied to organic materials easily. EEF treatment on a film is a remarkably simple process, which onlyinvolves positioning electrodes (positive/negative) at a certain distance apart in the air and applying the field for a specific duration.…”