Low operating voltage and low bias stress in top-contact SnCl2Pc/CuPc heterostructure-based bilayer ambipolar organic field-effect transistors

Abstract

Herein, a symmetrical Ag top contact-bottom gate (TC-BG) bilayer ambipolar organic field-effect transistor based on the heterojunction of vacuum-deposited small molecules, tin(IV) phthalocyanine dichloride (SnCl₂Pc) (n-channel) and copper phthalocyanine (CuPc) (p-channel), has been demonstrated. A hydroxyl-free poly(methyl methacrylate) (PMMA) with aluminum oxide (Al₂O₃) bilayer dielectric exhibits low operating voltage (∼10 V) and low bias stress (relaxation time τ ∼ 10⁵ s) for both n-channel and p-channel cases. The optimized SnCl₂Pc/CuPc heterostructure exhibits balanced carrier mobility and both types of charge carriers, electrons and holes, are facilitated by the same low work function Ag contact, depending on the bias conditions, from the TC-BG architecture. The Ag contact also exhibits Ohmic injection of charge carriers with low contact resistance in the n-channel region under an optimal heterostructure configuration. The contact resistance for electron and hole-injection is strongly dependent on the thickness of the SnCl₂Pc and CuPc layers, respectively. The bias stress stability is modeled using a stretched exponential fitting. Our results demonstrate that the ambipolar device characteristics and performance can be controlled by adjusting the thickness of the molecular layer, which is highly desirable. Such simple heterostructure engineering with utilization of organic molecular semiconductors can truly enable the development of promising low-cost and flexible organic electronics for extensive applications.