Controlling contact resistance in top-gate polythiophene-based field-effect transistors by molecular engineering

We report on an effective control of source–drain contact resistance by insertion of a self-assembled monolayer at the metal/semiconductor interface in top-gate staggered polymer field-effect transistors fabricated with poly(2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT). The device performance can be dramatically improved by introducing a fluorinated alkyl-thiol, 1H, 1H, 2H, 2H-perflourodecanethiol (PFDT) on the gold source–drain contacts. The PFDT-induced interface dipole and hydrophobic surface enables both a favourable shift of work function lowering the hole injection barrier via dipole alignment and a large crystal growth of pBTTT film with a unique lamellar morphology near to the contact. The optimized device with PFDT-modified gold contact plus OTS-treated substrate exhibits a high field-effect mobility above 0.4 cm² V⁻¹ s⁻¹and low contact resistance of 0.45 MΩ at the gate voltage of −60 V.