A simple method for controllable solution doping of complete polymer field-effect transistors

Controllable p-type doping of both poly(3-hexylthiophene) (P3HT) and poly(triarylamine) (PTAA) organic field effect transistors (OFETs) was achieved by immersing complete top-contact OFETs in a solution of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) in acetone. As this method is applied to complete devices, it has a greater utility than methods involving doping of the solution prior to film deposition as it allows separation of the device processing and doping steps, facilitating the use of optimal processing conditions at each stage. It was found that by varying immersion time and the concentration of the dopant solution, it was possible to vary the threshold voltage for a P3HT OFET by over 30 V. Although PTAA devices are less sensitive to oxidation by F4-TCNQ than OFETs using P3HT, they can also be controllably doped by this method up to a threshold voltage of +12 V.