Thin-Film Morphology of Inkjet-Printed Single-Droplet Organic Transistors Using Polarized Raman Spectroscopy: Effect of Blending TIPS-Pentacene with Insulating Polymer

Abstract

We report thin-film morphology studies of inkjet-printed single-droplet organic thin-film transistors (OTFTs) using angle-dependent polarized Raman spectroscopy. We show this to be an effective technique to determine the degree of molecular order as well as to spatially resolve the orientation of the conjugated backbones of the 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene) molecules. The addition of an insulating polymer, polystyrene (PS), does not disrupt the π-π stacking of the TIPS-Pentacene molecules. Blending in fact improves the uniformity of the molecular morphology and the active layer coverage within the device and reduces the variation in molecular orientation between polycrystalline domains. For OTFT performance, blending enhances the saturation mobility from 0.22 ± 0.05 cm(2)/(V·s) (TIPS-Pentacene) to 0.72 ± 0.17 cm(2)/(V·s) (TIPS-Pentacene:PS) in addition to improving the quality of the interface between TIPS-Pentacene and the gate dielectric in the channel, resulting in threshold voltages of ∼0 V and steep subthreshold slopes.

One-dimensional self-confinement promotes polymorph selection in large-area organic semiconductor thin films

“…For example, the rather straightforward approach of drop casting usually results in non-uniform films 20 . Inkjet printing, spraycoating and spin coating have also been used to prepare highmobility OTFTs from a variety of OSCs [21][22][23][24] . These methods generally yield little preferential crystallographic orientation in the plane of the generated thin films without additional patterning processes.…”

1 GHz Pentacene Diode Rectifiers Enabled by Controlled Film Deposition on SAM‐Treated Au Anodes

“…[20][21][22] The effect that such structural differences have on electrical characteristics for transport in the vertical direction (normal to the fi lm plane) has not been investigated to any great extent; the great majority of studies have focused on in-plane transport within TFT structures. [23][24][25] In this study, we investigated vertical diode structures instead of TFTs and as a result of the understanding gained we were able to fabricate ultrafast pentacene rectifi ers with V out = 3.8 V at 1 GHz and with a 3 dB frequency, in terms of voltage, of 1.24 GHz, the highest value reported to date. [ 8 ] Conjugated organic molecules such as pentacene, demonstrate strong electron-vibrational mode coupling with a dependence on orientation.…”

In-situ monitoring of molecular vibrations of two organic semiconductors in photovoltaic blends and their impact on thin film morphology

“…6,7 Raman spectroscopy is an inelastic light scatteringbased technique which probes the vibrational modes of a material and it is a very valuable tool to probe the morphology of conjugated polymer:fullerene thin films. [8][9][10][11][12] It has a number of advantages including probing molecular order, 8,12,13 molecular orientation, 14,15 in-situ chemical reactions, [16][17][18] and chemical mapping. 9,12,19 Although Raman spectroscopy is a valuable tool to study the morphology of conjugated polymer:fullerene films, usually Raman spectrum of only one component (polymer) is probed.…”