Liquid crystals for organic thin-film transistors

Hiroaki Iino,Takayuki Usui,Jun-Ichi Hanna

doi:10.1038/ncomms7828

Hiroaki Iino, Takayuki Usui + Show 1 more

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https://doi.org/10.1038/ncomms7828

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Abstract

Crystalline thin films of organic semiconductors are a good candidate for field effect transistor (FET) materials in printed electronics. However, there are currently two main problems, which are associated with inhomogeneity and poor thermal durability of these films. Here we report that liquid crystalline materials exhibiting a highly ordered liquid crystal phase of smectic E (SmE) can solve both these problems. We design a SmE liquid crystalline material, 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10), for FETs and synthesize it. This material provides uniform and molecularly flat polycrystalline thin films reproducibly when SmE precursor thin films are crystallized, and also exhibits high durability of films up to 200 °C. In addition, the mobility of FETs is dramatically enhanced by about one order of magnitude (over 10 cm2 V−1 s−1) after thermal annealing at 120 °C in bottom-gate-bottom-contact FETs. We anticipate the use of SmE liquid crystals in solution-processed FETs may help overcome upcoming difficulties with novel technologies for printed electronics.

Highlights

Crystalline thin films of organic semiconductors are a good candidate for field effect transistor (FET) materials in printed electronics
High mobilities have been achieved in solutionprocessed organic field effect transistors (OFETs) fabricated with polycrystalline thin films of small molecules, including TIPS-pentacene[1] and 2,7-dialkyl[1]benzothieno[3,2-b][1]benzothiophene[2]
Bottom-gate and top-contact type FETs were fabricated with polycrystalline thin films of Ph-BTBT-10 on SiO2 (300 nm)/Si-substrates to allow the characterization of this compound as an OFET material

Summary

Introduction

Crystalline thin films of organic semiconductors are a good candidate for field effect transistor (FET) materials in printed electronics. We design and synthesize the SmE liquid crystalline material of 2-decyl-7-phenyl-benzothienobenzothiophene (Ph-BTBT-10, Fig. 1a) for OFETs and describe the phase transition behaviour, the crystallographic properties and the fabrication of its crystalline thin films by spin coating and their application to FET devices.

Results

Conclusion