Heavily N-doped monolayer graphene electrodes used for high-performance N-channel polymeric thin film transistors

Abstract

Recently graphene attracted much attention as a promising electrode material for organic field effect transistors (OFETs). However the electrodes used in most of the graphene-based OFETs were prepared from pristine graphene which suffers from relatively low conductivity and poor controlling of work function. In this work, we report the N-doping by Cs₂CO₃ of the CVD-grown single-layer graphene (SLG) via a facial spin-coating process. The Cs₂CO₃-engineered SLGs exhibit a heavy and stable N-doping, as well as significantly decreased work function (3.9 eV) compared to pristine graphene. The doped graphene was used as the source/drain electrodes in the bottom-contact top-gated OFETs based on a good electron transporter poly{[N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)). The polymeric FETs show an enhancement of electron mobility by a factor of 10, as well as a reduction of contact resistance compared to the devices using pristine graphene. It is attributed to a remarkable lowering of electron injection barrier at the polymer/graphene electrode due to the decreased work function of graphene. In addition, the microstructural observations reveal that the face-on molecular packing and morphological feature do not change for the P(NDI2OD-T2) films coated on the doped graphene electrodes compared to those on the SiO₂ dielectric, in spite of a highly hydrophobic surface of the graphene.