Role of Perfluorophenyl Group in the Side Chain of Small-Molecule n‑Type Organic Semiconductors in Stress Stability of Single-Crystal Transistors

Operational
stability, such as long-term ambient durability and
bias stress stability, is one of the most significant parameters in
organic thin-film transistors (OTFTs). The understanding of such stabilities
has been mainly devoted to energy levels of frontier orbitals, thin-film
morphologies, and device configuration involving gate dielectrics
and electrodes, whereas the roles of molecular and aggregated structural
features in device stability are seldom discussed. In this Letter,
we report a remarkable enhancement of operational stability, especially
bias stress, of n-channel single-crystal OTFTs derived from a replacement
of phenyl with perfluorophenyl groups in the side chain. Because of
the several-molecule-thick single-crystal nature employed for the
OTFTs, the crystal-surface properties are thought to be critical,
where the surface structure composed of perfluorophenyl moieties could
suppress interactions between environmental species and field-induced
carriers owing to increased hydrophobicity and steric protection of
π-conjugated units.

操作稳定性（包括长期环境耐久性与偏压应力稳定性）是有机薄膜晶体管（organic thin-film transistors, OTFTs）最为关键的性能参数之一。目前学界对这类稳定性的研究主要聚焦于前线轨道能级、薄膜形貌以及包含栅介质与电极的器件构型，而分子与聚集态结构特征对器件稳定性的作用却鲜有探讨。在本研究快报中，我们报道了一类通过将侧链中的苯基替换为全氟苯基制备得到的n型沟道单晶有机薄膜晶体管，其操作稳定性——尤其是偏压应力稳定性——得到了显著提升。由于本次研究所用OTFT器件为数分子层厚度的单晶结构，晶体表面特性被认为是核心影响因素：由全氟苯基基团构成的表面结构，可通过增强疏水性以及对π共轭单元的空间位阻保护，抑制环境介质与场致载流子之间的相互作用。