The Effect of Alkyl Chain Length in Organic Semiconductor and Surface Polarity of Polymer Dielectrics in Organic Thin‐Film Transistors (OTFTs)

Abstract

The interface between dielectric and organic semiconductor is critically important in determining organic thin‐film transistor (OTFT) performance. Surface polarity of the dielectric layer can hinder charge transport characteristics, which has restricted utilization of polymeric dielectric materials containing polar functional groups. Herein, the electrical characteristics of OTFTs are analyzed depending on the alkyl chain length of organic semiconductors and surface polarity of polymer dielectrics. High‐performance dibenzothiopheno[6,5‑b:6′,5′‑f]thieno[3,2‑b]thiophene (DBTTT) and newly synthesized its alkylated derivatives (C6‐DBTTT and C10‐DBTTT) are utilized as organic semiconductors. As dielectric layers, non‐polar poly(1,3,5‐trimethyl‐1,3,5‐trivinylcyclitrisiloxane) (pV3D3) and poly(2‐cyanoethyl acrylate‐co‐diethylene glycol divinyl ether) [p(CEA‐co‐DEGDVE)] with polar cyanide functionality are utilized. The fabricated OTFTs with pV3D3 commonly exhibit the excellent charge transport characteristics. In addition, the OTFT performance is improved with lengthening the alkyl chain in organic semiconductors, which can be attributed to the molecular orientation of semiconductors. On the other hand, non‐alkylated DBTTT OTFTs with polar p(CEA‐co‐DEGDVE) show relatively poor electrical characteristics, while their performance is drastically enhanced with the alkylated DBTTTs. The ultraviolet photoelectron spectroscopy (UPS) reveals that surface polarity of the dielectric layer can be abated with alkyl chain in organic semiconductors. It is believed that this study can provide a useful insight to optimize dielectric/semiconductor interface to achieve high‐performance OTFTs.

Controlling Fluorination Density of Soluble Polyimide Gate Dielectrics and its Influence on Organic Crystal Growth and Device Operational Stability

“…The surface, bulk, and interface properties of thin films can be modulated by adjusting the interactions across the macroscopic and atomic scales using molecular-level engineering. − These thin-film properties play notable roles in organic electronics to meet the requirements of next-generation electronics such as printed logic circuits, flexible transistor arrays, and stretchable light-emitting diodes. A gate dielectric layer, which is among the most critical components affecting device performance, and its feasibility in organic field-effect transistors (OFETs) are assessed for (i) good compatibility with organic channel materials and flexible substrates, (ii) compatibility with conventional large-area film deposition methods, (iii) excellent capacitive and insulating properties, (iv) colorless and transparent optical properties, and (v) excellent stability during postdeposition processes. ,− Moreover, controlling the molecular interaction at the interfaces with active layers, which is dominant when the device is in operation, is essential. − For example, gate dielectric materials with polar surface characteristics, which is typical for high dielectric constant materials, may lead to increased charge-trapping sites at their interface with the active layer and band broadening of organic semiconductor (OSC) molecules. − …”