Probing bias stress effect and contact resistance in bilayer ambipolar organic field-effect transistors

The bilayer ambipolar organic field-effect transistors (OFETs) based on 1,8-naphthoylene(trifluoromethylbenzimidazole)-4,5-dicarboxylic acid imide (NTFBII)/pentacene heterojunction have been probed. The origin of the bias stress instability in the top n-channel is attributed to the electron trapping at the NTFBII/pentacene interface, whereas the bias stress effect in the bottom p-channel is associated mainly with the pentacene/dielectric interface. The contact resistances for electron and hole injection are strongly dependent on the local conductivity of the NTFBII and pentacene layers, respectively. The Cu penetration into NTFBII to form direct contact to pentacene is proposed to be the hole injection mechanism in the bilayer ambipolar OFETs.