High performance polythiophene thin-film transistors doped with very small amounts of an electron acceptor

The relationship between the electrical properties and the microstructure of poly(3-hexylthiophene) (P3HT) films doped with an electron acceptor, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) has been studied. The introduction of F4-TCNQ in very small quantities improved the device performance of P3HT thin-film transistors significantly. The field-effect mobility of a device doped with only 0.2wt% F4-TCNQ was enhanced by a factor of 30 with respect to that of a pure P3HT device. The threshold voltages of the P3HT thin-film transistors can also be controlled by adjusting the F4-TCNQ concentration. These improvements are attributed to the doping-induced formation of charge-transfer complexes and improved molecular orientation of the P3HT.