Dependence of field-effect mobility and contact resistance on nanostructure in regioregular poly(3-hexylthiophene) thin film transistors

The mobility and contact resistance of transistors based on regioregular poly(3-hexylthiophene) (P3HT) with Ti/Pt electrodes were investigated as a function of the molecular weight (M-W) of P3HT. For an increase in M-W from 5.5 to 11 kDa, the mobility increased from 0.04 to 0.16 cm(2) V-1 s(-1), whereas the contact resistance decreased from 1.7 to 0.6 M Omega. Further increases in M-W yielded an apparent saturation in both the mobility and the contact resistance. A nanofibrilar morphology was observed where the width of the nanofibrils increases with M-W. A qualitative model based on polymer chain folding is proposed to explain the electrical results. (c) 2008 American Institute of Physics.