Effects of Fluid Behavior on the Electrical Characteristics of Inkjet-Printed Thin-Film Transistors

An approach to control the carrier transport characteristics of inkjet-printed organic field-effect transistors (OFETs) was developed by creating concentration gradients within a printed volume of liquid. The gradients, established by precise and systematic spatial manipulation of the jetted droplets, were used to control the film formation of poly(3-hexylthiophene-2,5-diyl) (P3HT) to improve the carrier transport properties of the OFETs. The introduction of an internal lateral flux influenced the molecular alignment of the formed P3HT film. This alignment could be fixed parallel to the current flow direction in the device. The resulting printed P3HT-based transistors had an extracted field-effect mobility of 0.022 cm2/V·s, a 7 times enhancement compared to devices printed without a lateral flux. The off current for the printed devices ranged from 1 × 10–8 to 2 × 10–11 A with nominal threshold voltages <5 V. A simple geometric model was developed to describe how the control of the placement of the jetted droplets and the liquid volume over the device area may be used to affect film formation during the drying process. The model was used to predict and correlate the critical printing parameters to the thin-film structural profile and the observed device performance.