Improving the charge transport performance of solution-processed organic field-effect transistors using green solvent additives

Abstract

In this study, we explored the effect of binary solvent systems based on green solvent additives to form pre-aggregated solution and solution-processed organic semiconductor films for organic field-effect transistors (OFETs) and to aim at minimizing the use of classical toxic solvents. Common organic semiconductors (OSCs), including p- and n-channel small molecules and polymers such as 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene), 2,7-diocyl[1]benzothieno[3,2-b][1]benzothiophene (C₈-BTBT), 4,4′-(2λ⁴σ²-benzo[1,2-c:4,5-c′]bis[1,2,5]thiadiazole-4,8,diyldi-5,2-thiophenediyl)bis[2-dodecylbenzonitrile] (TU-3), and poly{N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)), were used to demonstrate the wide applicability of green solvent additives as non-solvents in binary solvent systems. To select appropriate green solvent additives and increase their use while reducing that of toxic solvents, the dielectric constant, boiling point, and Hansen solubility parameters (HSP) were considered. UV-vis spectroscopy analysis of OSC solutions clearly showed the formation of pre-aggregation through the shifts of the peak wavelength. Fabricated semiconductor films were investigated by atomic force microscopy (AFM) and θ–2θ X-ray diffraction (XRD) to clarify the improved film morphology/microstructure for better charge transport characteristics. As a relevant result, the mobility of the resulting OFETs was significantly improved by 3–8 times with a careful selection of the appropriate amount of green solvent additives. Furthermore, green solvent addition allowed the enhancement of the electrical performance of p- and n-channel organic semiconductors, affording the fabrication of bulk-heterojunction ambipolar transistors and complementary-like inverters with better performance.