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 polymeric-interfacial 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.