Precise Control of Crystal Orientation of Conjugated Molecule Enables Anisotropic Charge Transport Properties

Abstract The crystal orientation of small molecules is one of the key parameters for developing high‐performance small molecule based organic field‐effect transistors. However, achieving a high degree of backbone alignment still remains a challenge, due to the sensitive nature of small molecules to processing conditions. Herein, the thin films of three conjugated small molecules, named as ZR1, ZR2‐C3, and Y6 are prepared by epitaxial‐crystallization on a highly oriented polyethylene (PE) substrate, resulting in the significant enhancement in charge transport properties. The maximum mobilities for aligned edge‐on molecules in the films enhance by up to 9.91 × 10 −2 and 8.97 × 10 −2 cm 2 V −1 s −1 for ZR1 and ZR2‐C3 films with conducting channel along small molecule backbones, which are 35‐ and 37‐fold that of the values evaluated in perpendicular to molecular backbones and nearly 23‐and 19‐fold beyond the values measured from unaligned films. Furthermore, the electron and hole mobilities of the small molecule Y6 with face‐on nature increase by nearly fourfold the values measured in perpendicular to the backbone direction and from unaligned films. This work demonstrates the epitaxial crystallization of thin films on oriented PE, offers a critical understanding of small molecules with different orientations and an effective approach for tuning charge transport toward high‐performance organic electronic applications.