Centro-Apical Self-Organization of Organic Semiconductors in a Line-Printed Organic Semiconductor: Polymer Blend for One-Step Printing Fabrication of Organic Field-Effect Transistors.

Su Jin Lee,Yong-Won Song,Jung Ah Lim,Jinhan Cho,So Young Yeo,Yong-Jae Kim,Eunji Lee,Min Kim,Ho Sun Lim

doi:10.1038/srep14010

Abstract

Here we report the first demonstration for centro-apical self-organization of organic semiconductors in a line-printed organic semiconductor: polymer blend. Key feature of this work is that organic semiconductor molecules were vertically segregated on top of the polymer phase and simultaneously crystallized at the center of the printed line pattern after solvent evaporation without an additive process. The thickness and width of the centro-apically segregated organic semiconductor crystalline stripe in the printed blend pattern were controlled by varying the relative content of the organic semiconductors, printing speed, and solution concentrations. The centro-apical self-organization of organic semiconductor molecules in a printed polymer blend may be attributed to the combination of an energetically favorable vertical phase-separation and hydrodynamic fluids inside the droplet during solvent evaporation. Finally, a centro-apically phase-separated bilayer structure of organic semiconductor: polymer blend was successfully demonstrated as a facile method to form the semiconductor and dielectric layer for OFETs in one- step.

Highlights

The printed feature is strongly dependent on the printing conditions, such as the solvents, solution concentration, and surface wettability of the substrate[6,7,8,9,10]
Blend. 2,8-Difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene(diF-TESADT), a small molecule semiconductor with a large charge carrier mobility, was blended with an insulating polymer, poly(methyl methacrylate) (PMMA). 10 wt% solution of the 1:4 blend of diF-TESADT and PMMA was printed onto a UV-ozone-treated silicon wafer using a picoliter fluidic dispenser, where the ultrasonic vibrations cause the fluid to be ejected from the tip of the micropipette and to form a fluidic meniscus at the end of the tip that is touching the surface of the substrate (Fig. 1a)[23]
Film characterization conducted by using cross-section-scanning electron microscopy (SEM), EDX, TOF-SIMS, and X-ray photoelectron spectroscopy (XPS) confirmed that the diF-TESADT in the printed diF-TESADT:PMMA blends vertically segregated and simultaneously self-assembled to form a crystalline structure near the centerline of the printed line

Summary

Introduction

The printed feature is strongly dependent on the printing conditions, such as the solvents, solution concentration, and surface wettability of the substrate[6,7,8,9,10]. Blending polymeric binder is an important strategy for formation of uniform films with small-molecule organic semiconductors, such as 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN), triethylsilylethynyl anthradithiophene (TES-ADT), 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TESADT), and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT)[4,16,17,18,19,20]. Key feature of our finding is that the organic semiconductor molecules were vertically segregated onto the top of polymer phase and simultaneously crystallized at the center region of the printed line pattern just after the solvent evaporation process without an additive process We justify this self-organization of the organic semiconductor in the confined blend solution through the use of the term “centro-apical self-organization” throughout the remainder of the paper. The actual OFETs consisted of the centro-apically phase-separated organic semiconductor channel and a gate dielectric of an underlying polymer matrix exhibited a good performance approaching previously reported values of devices prepared via either the spin-casting or drop-casting methods

Methods

Results

Conclusion