(28f) Dynamic-Template-Directed Assembly of 2D Monolayer Films of Conjugated Polymers and Their Distinct Electronic Properties
AIChE Annual Meeting
2020
2020 Virtual AIChE Annual Meeting
Materials Engineering and Sciences Division
Polymer Crystallization and Semi-Crystalline Polymers
Monday, November 16, 2020 - 9:15am to 9:30am
In this talk, we present dynamic-template-directed meniscus-guided coating as a new technique to fabricate 2D monolayer films of conjugated polymers over large area using a wide-processing window. By utilizing two donor-acceptor polymers, DPP2T-TT and PII-2T, we demonstrate that the dynamic-template enhances polymer 2D crystallization resulting in 2D monolayer films with highly ordered and aligned polymer backbone with edge-on ð-ð stacking. In contrast, the monolayer films on solid static substrates resulted in discontinuous morphology exhibiting 1D fiber-network with strong alkyl-chain stacking peaks at the expense of backbone stacking. As a result, charge transport was only observed on monolayer films printed on dynamic-template but not on those printed on solid substrates. As thickness was increased from monolayers to multi-layers, the polymer ð-stacks changed from edge-on to bimodal orientation when the film reached a critical thickness of ~20 nm. UV-Vis spectroscopy and cyclic voltammetry analysis disclosed abrupt rise in J-aggregation, absorption coefficient and decrease in band gap and HOMO level until the film reached a critical thickness, possibly arising from straightened polymer backbone. Furthermore, increase in film thickness resulted in drastic increase of hole mobility in the polymer films, peaking at 0.7 cm2V-1s-1 near the critical thickness, which further corroborated with drastic planarity of polymer backbone with increase in film thickness. Finally, we also fabricated of organic field-effect transistor based chemical sensors incorporating DPP2T-TT films of varying thicknesses and demonstrated ultrahigh sensitivity (~83%) of ultrathin films of ~7 nm thickness (bilayers) to ammonia vapors of 1 ppb concentration.