Solvent-dependent performance of solution-processed small-molecule organic field-effect transistors

We investigated the morphology and crystallinity of 2,7-Dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) thin films formed by the solution-shearing method using dichlorobenzene (DCB) or toluene as the solvent for the C8-BTBT solution. In addition, we investigated the effects of the solvents on the performance of C8-BTBT-based organic field-effect transistors (OFETs). Based on the electrical properties of the C8-BTBT-based OFETs, it was observed that the performance of the OFETs with the C8-BTBT films formed using the DCB solvents, which have a high boiling point (180.5 °C), depended strongly on the processing method and the surface condition of the substrate, affording high-performance C8-BTBT-based OFETs with a reasonably high mobility of 0.52 cm²V⁻¹s⁻¹; however, the OFETs fabricated with toluene-based C8-BTBT solutions, which have a relatively low boiling point (111 °C), resulted in similar mobility values from 0.01 to 0.05 cm²V⁻¹s⁻¹, regardless of the coating method and the surface state of the substrate. The experimental results reveal that the process conditions that allow the solvent to be confined for a sufficient amount of time in order to form C8-BTBT thin films play an important role in the fabrication of solution-processed high-performance OFETs.