2D molecular crystal templated organic p–n heterojunctions for high-performance ambipolar organic field-effect transistors

Abstract

Bilayer p–n heterojunctions are promising structures to achieve high-performance ambipolar organic field-effect transistors (aOFETs). However, the performance of aOFETs based on polycrystalline bilayer p–n heterojunctions was substantially reduced compared with that of their unipolar devices due to the unavoidable interlayer mixing in bilayer heterojunctions fabricated by conventional methods such as two-step spin-coating or vacuum-deposition. Herein, the interlayer mixing problem was reduced by 2D molecular crystal (2DMC) templated growth of high-quality bilayer p–n heterojunctions. Due to the excellent wettability of the 2DMC template for organic semiconductors, the grain size of the upper layer was substantially enlarged. Moreover, the atomically flat surface and the long-range order of the 2DMC template reduced the common interlayer mixing problem. As a result, the mobility of copper hexadecafluorophthalocyanine (F₁₆CuPc) increased over one order of magnitude compared with that of their unipolar devices. Actually, the electron mobility of 0.56 cm² V⁻¹ s⁻¹ was the highest among both ambipolar OFETs and unipolar OFETs adopting F₁₆CuPc as the n-type semiconductor.