Role of liquid substrates in the self-assembly and charge transport of 2D organic semiconductors

Manipulating and understanding the crystallization processes of solution processed organic thin films have been a key challenge not only for fundamental studies but also for intrinsic charge transport properties. Among various techniques, formation of self-assembled thin films at liquid–air interface has been known for polymeric semiconductors. However, integration of this technique for organic small molecules (OSM) is scarcely explored. This sought-after exploration results in possibilities of integrating the superior charge transport properties of OSM with other fabrication advantages of liquid substrate-based growth methods. In this work, self-assembly of an OSM-based semiconductor over a liquid–air interface is thoroughly investigated using the 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8BTBT) molecule and its crystallization behaviour along with morphology is studied over different liquid base substrates (LBSs). The correlation of the morphology change due to the change in the surface tension and viscosity of the LBS is stated and the resulting films are investigated for charge transport properties of C8BTBT based field-effect transistors. The ribbon-like morphology emerges for the low surface tension LBS, which gives rise to higher charge transport among the films. This study provides a novel and easy processing technique with a better understanding of the growth mechanism for large area and highly crystalline thin films of organic small molecule semiconductor-based electronic devices.