Insulating Polymer Blend Organic Thin-Film Transistors Based on Bilayer-Type Alkylated Benzothieno[3,2-<i>b</i>]naphtho[2,3-<i>b</i>]thiophene
Ryo Miyata, Satoru Inoue, K. Nakajima, Tatsuo Hasegawa
Abstract
Herein, we developed a practical method to produce high-performance organic thin-film transistors (OTFTs) based on highly layered crystalline organic semiconductors (OSCs) that form bilayer-type layered herringbone (b-LHB) packing and exhibit high intrinsic mobility. We applied the insulating polymer blend technique using a typical b-LHB OSC of 2-octyl-benzothieno[3,2-b]naphtho[2,3-b]thiophene (2-C8-BTNT) and fabricated polycrystalline thin-film transistors (TFTs) via short-duration spin coating and subsequent annealing. The use of blends and the choice of polymer additive strongly affected the performance of the polycrystalline TFTs, and poly(methyl methacrylate) (PMMA) blend TFTs exhibited a high mobility exceeding 4 cm2/(V s) and small device-to-device variations. Using extended techniques in atomic force microscopy (AFM), we investigated the thin-film morphologies by bimodal AFM and the carrier transport properties by Kelvin probe force microscopy (KPFM). We demonstrated that the PMMA blend system enables the formation of a well-ordered polycrystalline thin film induced by vertical phase separation between the OSC and PMMA over a large area, resulting in uniform TFT performance. These findings pave the way for obtaining high-performance TFTs using simple processes, representing a substantial advancement toward the realization of printed electronics.