This study focuses on the microstructural modifications of regioregular poly(3-hexylthiophene) (rr-P3HT) in the small active channel of thin-film transistors (TFTs) during operations. Polarized absorption and micro-Raman spectroscopy analyses allow us to probe directly the conformation transitions of rr-P3HT chains parallel or perpendicular to the channel by means of exciton bandwidth, interchain electronic coupling, and effective conjugation length. The results of absorption spectra and a joint experimental-theoretical study of Raman spectra show that an external source-to-drain electric field can align rr-P3HT chains parallel to the channel, improving electrical performance after long-term operations, especially charge transport properties. In comparison, the applied external gate field induced an increase in amorphous fraction of the rr-P3HT films. After the analysis, we propose a chain rearrangement model driven by an external electric field to interpret the changes of the effective conjugation length of rr-P3HT, rather than thermal annealing. Our observations provide a thorough explanation for the previously unknown relationships of structure-electronic properties under the extended operations of polymer TFT devices.

We report an unexpected improvement in the microstructural and electrical properties of regioregular poly(3-hexylthiophene) (P3HT) as an active layer in field-effect transistors (FETs) by introducing soft insulating chains from poly(methyl methacrylate) (PMMA) as a cover layer in a solvent modedependent manner. A joint experimental and theoretical spectroscopic and electrical analysis is provided to study the P3HT/PMMA bilayer films with semi-interpenetrating semiconducting/ insulating interlocked interdiffusion microstructures. Absorption and Raman studies reveal that disordered P3HT chains in films cast from a low-boiling point (bp) solvent favor reorganization into more ordered structures during PMMA covering, thus enhancing the electrical and switch behaviors of FETs. Although high-bp solvents initially create highly crystalline P3HT films, the films are significantly destroyed after the deposition of the PMMA layer, thus dramatically degrading FET characteristics. The semi-interpenetrating semiconducting/insulating microstructures in the designed bilayer films indicate the possibility of ameliorating field-effects in polymer FETs, especially in subthreshold swing and switch on-off behaviors.