Wettability Control of Interfaces for High-Performance Organic Thin-Film Transistors by Soluble Insulating Polymer Films.

Tao Shen,Xue Liu,Zilu Yang,Hui Zhou,Jinhua Li,Ming Zhang,Yue Fan,Qin Fan,Debesh Devadutta Mishra,Xianbao Wang

doi:10.1021/acsomega.0c00548

Abstract

Organic small-molecule semiconductors have higher carrier mobility compared to polymer semiconductors, while the actual performances of these materials are susceptible to morphological defects and misalignment of crystalline grains. Here, a new strategy is explored to control the crystallization and morphologies of a solution-processed organic small-molecule semiconductor 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) using soluble polymer films to control the wettability of substrates. Different from the traditional surface modification method, the polymer layer as a modification layer is soluble in the semiconductor solution during the fabrication of organic thin-film transistors (OTFTs). The dissolved polymer alters the state of the semiconductor solution, which in turn, changes the crystallographic morphologies of the semiconductor films. By controlling the solubility and thickness of the polymer modification layers, it is possible to regulate the grain boundary and domain size of C8-BTBT films, which determine the performances of OTFTs. The bottom-gate transistors modified by a thick PS layer exhibit a mobility of >7 cm2/V·s and an on/off ratio of >107. It is expected that this new modification method will be applicable to high-performance OTFTs based on other small molecular semiconductors and dielectrics.

Highlights

Blending a small molecular semiconductor with an insulating polymer has successfully been realized as an effective way to solve this problem.[13−18] The addition of the polymer can increase the uniformity of the films and induce spontaneous vertical phase separation, which results in efficient charge transport.[19−21] The microstructures of the blend films are affected by various interactions such as solute− substrate, solute−solvent, and solute−solute interactions during the solvent evaporation.[11,22−26] To further develop polymer−small molecule blended Organic thin-film transistors (OTFTs) with desired properties, much effort has been devoted to engineering interfaces to control the crystallographic morphologies and phase-separated structures of blend films
The crystallization and morphology of the films were thereby effectively controlled by the addition of a soluble polymer in Figure 1a shows the schematic diagram of our experimental system, which describes the formation process of an organic small molecular semiconductor thin film
A new method is provided for improving the performances of solution-processed C8-BTBT OTFTs

Summary

■ INTRODUCTION

Organic thin-film transistors (OTFTs) have received much attention due to their solution-processable and low-temperature processes.[1−6] Among the solution-processable organic semiconductors, small molecules usually possess higher fieldeffect mobilities compared to polymers.[7−9] the strong π−π interactions between small molecules and the low viscosity of the solutions often lead to inhomogeneous nucleation and dewetting of films from substrates.[10−12]. Self-assembled monolayers (SAMs),[27−29] UV−ozone interface modification,[30] and selective-dewetting pattern[31,32] were the commonly used methods to improve the qualities of blend films. These methods were committed to change the surface energy of the interface. Commonly used SAMs, such as OTS and HMDS, have low surface energies, which prevented the wetting of the solution on the substrate Another kind of modification method to control the crystallization of small molecules is to engineer the surface with soluble polymer films. Spin-coated blend semiconductor films with the modification of soluble polymer films have not been

■ RESULTS AND DISCUSSION

Ctotal

■ CONCLUSIONS

■ REFERENCES