Uniaxial orientation of P3HT film prepared by soft friction transfer method

Masayoshi Imanishi,Daisuke Kajiya,Tomoyuki Koganezawa,Ken-ichi Saitow

doi:10.1038/s41598-017-05396-9

Masayoshi Imanishi, Daisuke Kajiya + Show 2 more

Open Access

https://doi.org/10.1038/s41598-017-05396-9

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Abstract

The realization of room-temperature processes is an important factor in the development of flexible electronic devices composed of organic materials. In addition, a simple and cost-effective process is essential to produce stable working devices and to enhance the performance of a smart material for flexible, wearable, or stretchable-skin devices. Here, we present a soft friction transfer method for producing aligned polymer films; a glass substrate was mechanically brushed with a velvet fabric and poly(3-hexylthiophene) (P3HT) solution was then spin-coated on the substrate. A P3HT film with a uniaxial orientation was obtained in air at room temperature. The orientation factor was 17 times higher than that of a film prepared using a conventional friction transfer technique at a high temperature of 120 °C. In addition, an oriented film with a thickness of 40 nm was easily picked up and transferred to another substrate. The mechanism for orientation of the film was investigated using six experimental methods and theoretical calculation, and was thereby attributed to a chemical process, i.e., cellulose molecules attach to the substrate and act as a template for molecular alignment.

Highlights

Optoelectronic properties can be improved by the anisotropy of molecules in a solid
The proposed method is not conducted at high temperature (140–180 °C), such as with conventional frictional transfer, but is established at room temperature
This is attributed to cellulose, which is consistent with the TOF-SIMS results (Fig. S2). These results indicate that cellulose is transferred from the velvet fabric to the substrate surface and acts as a template for the alignment of P3HT molecules

Summary

Introduction

Optoelectronic properties can be improved by the anisotropy of molecules in a solid. The molecular orientation in conjugated polymers has attracted particular attention in the chemical research field and for practical applications[1,2,3,4,5] Oriented polymer films have been utilized for flexible, lightweight, printed electronics, such as wearable or stretchable-skin devices[6, 7], solar cells[8], light-emitting diodes[9], and transistors[10,11,12]. Several methods to prepare highly oriented polymer films have been reported, such as drawing, rubbing, friction transfer, alignment on a specific substrate, and directional crystallization[13,14,15,16,17,18,19,20]. Facile methods have been previously reported, whereby molecules are oriented by drop casting and/or spin coating on a substrate mechanically brushed by a fabric[4, 27, 28], a tissue paper[29], or a paper[28] Such methods can provide orientated films composed of small molecules[29], liquid crystals[27, 28], and oligomers[4] at room temperature; the molecular orientation of polymers has not yet been reported. A polarized light-emitting device was demonstrated using an oriented polymer film prepared by soft friction transfer

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