The Role of Tie Chains on the Mechano-Electrical Properties of Semiconducting Polymer Films

The mechano-electrical properties of poly(3-hexylthiophene) thin films are investigated as a function of their tie-chain content. Tie chains play an indispensable role in enabling strain-induced structural alignment and charge-transport enhancement in the strain direction. In the absence of sufficient tie chains, the external mechanical force cannot induce any significant polymer backbone alignment locally or crystallite reorientation at the mesoscale. These samples instead undergo brittle fracture on deformation, with cracks forming normal to the direction of strain; charge transport in this direction is hindered as a consequence. This mechanistic insight on strain alignment points to the promise of leveraging tie-chain fraction as a practical tuning knob for effecting the mechano-electrical properties in conjugated polymer systems.