title: Enhancing Carrier Mobilities in Organic Thin-Film Transistors Through Morphological Changes at the Semiconductor/Dielectric Interface Using Supercritical Carbon Dioxide Processing.
abstract: Charge-carrier mobilities in poly(3-hexylthiophene) (P3HT) organic thin-film transistors (OTFTs) increase 5-fold when OTFTs composed of P3HT films on trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane (FTS) monolayers supported on SiO2dielectric substrates (P3HT/FTS/SiO2/Si) are subjected to supercritical carbon dioxide (scCO2) processing. In contrast, carrier mobilities in P3HT/octadecyltrichlorosilane (OTS)/SiO2OTFTs processed using scCO2are comparable to mobilities measured in as-cast P3HT/OTS/SiO2/Si devices. Topographical images of the free and buried interfaces of P3HT films reveal that scCO2selectively alters the P3HT morphology near the buried P3HT/FTS-SiO2interface; identical processing has negligible effects at the P3HT/OTS-SiO2interface. A combination of spectroscopic ellipsometry and grazing-incidence X-ray diffraction experiments indicate insignificant change in the orientation distribution of the intermolecular π-π stacking direction of P3HT/FTS with scCO2processing. The improved mobilities are instead correlated with enhanced in-plane orientation of the conjugated chain backbone of P3HT after scCO2annealing. These findings suggest a strong dependence of polymer processing on the nature of polymer/substrate interface and the important role of backbone orientation toward dictating charge transport of OTFTs.
authors.forename: Ban Xuan
authors.initials: BX
authors.lastname: Dong
authors.forename: Jojo A
authors.initials: JA
authors.lastname: Amonoo
authors.affiliation: Department of Chemical and Biological Engineering, Princeton University , Princeton, New Jersey 08544, United States.
authors.forename: Geoffrey E
authors.initials: GE
authors.lastname: Purdum
authors.affiliation: Department of Chemical and Biological Engineering, Princeton University , Princeton, New Jersey 08544, United States.
authors.forename: Yueh-Lin
authors.initials: YL
authors.lastname: Loo
authors.forename: Peter F
authors.initials: PF
authors.lastname: Green
keywords: backbone orientation; conjugated polymer; ellipsometry; organic thin film transistor; scCO2 processing; self-assembled monolayers; structure-transport relationship