Facile conversion of polymer organic thin film transistors from ambipolar and p-type into unipolar n-type using polyethyleneimine (PEI)-modified electrodes

Abstract

We report here a successful polarity conversion of organic thin film transistors (OTFTs) based on several polymer semiconductors with low-lying LUMO (lowest unoccupied molecular orbital) energy levels (⩽−4eV) from ambipolar and even p-type into unipolar n-type devices using an ultrathin layer (∼2–5nm) of polyethyleneimine (PEI) to modify the source and drain contacts. The work function of gold is substantially reduced with the PEI layer on its surface, which effectively suppresses the injection of holes and thus enables electron-only charge transport of these polymers in OTFTs. This general approach of electrode work function modification broadens the scope of available polymer semiconductors for use in printed electronics where n-channel OTFTs are needed.