Augmenting n‑Type Performance of Ambipolar Top-Contact Organic Thin-Film Transistors by Self-Generated Interlayers

We report n-type performance enhancement of
an ambipolar donor−acceptor (D−A) polymer by suppressing
its p-type behavior using a simple and versatile methodology
of interlayer processing in top-contact organic field-effect
transistors. In this approach, a judiciously selected interlayer
material, polyethylene glycol (PEG), is codeposited as an
additive with the semiconducting polymer DPP-T-TT active
layer. During top-contact aluminum deposition, the PEG
molecules migrate from within the bulk film to the organic/Al
interface because of additive−metal interactions. The
formation of the PEG interlayer was confirmed by X-ray
photoelectron spectroscopy and its effect on the polymericinterfacial
microstructure was studied using angle-dependent grazing-incidence wide-angle X-ray scattering. We find that the
PEG interlayer has two significant contributions to the n-type characteristics of the device: it suppresses hole injection while
improving electron injection by tuning the effective work-function, and it enhances the order and crystallinity of the polymer at
the interface effectively enhancing charge mobility.