Enhanced & anisotropic charge transport in polymer-based thin-film transistors by guiding polymer growth

Ideal molecular features and microstructural properties of organic semiconducting thin films are being explored to achieve high-performance organic thin-film transistors (OTFTs). We prepared and processed hexamethylbenzene (HMB)/poly(3-hexylthiophene) (P3HT) mixtures using a thermal gradient system to fabricate P3HT-based OTFTs. In the thermal gradient system, the HMB separated from the HMB/ P3HT mixtures and crystallized along the sample movement direction. The crystallized HMB affected and guided the growth behavior of P3HT at the molecular level. Observations from joint microscopic and spectroscopic analyses revealed that the HMBprocessed P3HT (H-P3HT) thin film possessed anisotropic and improved microstructures, particularly in crystalline domains. The improved molecular features and microstructural properties of the H-P3HT thin film enhanced the intramolecular and intermolecular charge transport by extending the π-conjugation, decreasing the reorganization energy, and strengthening the π-π overlaps. The electrical performance of the H-P3HT OTFT was augmented significantly with respect to that of the spin-coated P3HT OTFT. In addition, the H-P3HT OTFT exhibited an anisotropic charge transport property, correlating with microstructure directionality and resulting from the difference in the directions of the π-π overlaps. This effective and simple technique can be applied to other device types and has the potential to achieve high-performance organic electronic/photonic devices.