Threshold voltage control of copper phthalocyanine based organic field-effect transistors with a poly (N-vinylcarbazole) buffer layer

Copper phthalocyanine (CuPc) based organic field-effect transistors (OFETs) with controllable threshold voltages (V_Ts) were demonstrated by inserting a poly(N-vinylcarbazole) (PVK) buffer layer between CuPc and SiO₂. The PVK buffer layer enhances the crystallinity and improves the morphology of CuPc film, resulting in higher mobility up to 8.6 × 10^-3 cm² V^-1 s^-1. The V_Ts of the device can be changed systematically from 63 to -10 V with the shift of starting V_GS from 100 to 0 V in a single device. The controllable V_T and much wider extend of V_T can be attributed to the Fowler-Nordheim tunneling of electrons into PVK buffer layer.