Maximized Hole Trapping in a Polystyrene Transistor Dielectric from a Highly Branched Iminobis(aminoarene) Side Chain

• Published in: ACS applied materials & interfaces Vol. 13; no. 29; pp. 34584 - 34596
• Main Authors: Zhang, Qingyang, Barrett, Brandon, Lee, Taein, Mukhopadhyaya, Tushita, Lu, Chengchangfeng, Plunkett, Evan C, Kale, Tejaswini, Chi, Chen, Livi, Kenneth J. T, McGuiggan, Patricia, Reich, Daniel H, Thon, Susanna, Bragg, Arthur E, Katz, Howard E
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 28.07.2021; American Chemical Society (ACS)
• Subjects: aromatic compounds; gate dielectric; highly branched phenylenediamine; hydrocarbons; insulators; layers; MATERIALS SCIENCE; multilayer dielectric; Organic Electronic Devices; organic transistor; phenylenediamine side chain; polymers; static charge storage; threshold voltage shift; highly branched phenylenediamine; static charge storage; organic transistor; phenylenediamine side chain; threshold voltage shift; multilayer dielectric; gate dielectric
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.1c03929

We synthesized highly branched and electron-donating side chain subunits and attached them to polystyrene (PS) used as a dielectric layer in a pentacene field-effect transistor. The influence of these groups on dielectric function, charge retention, and threshold voltage shifts (ΔV th) depending on their positions in dielectric multilayers was determined. We compared the observations made on an N-perphenylated iminobisaniline side chain with those from the same side chains modified with ZnO nanoparticles and with an adduct formed from tetracyanoethylene (TCNE). We also synthesized an analogue in which six methoxy groups are present instead of two amine nitrogens. At 6 mol % side chain, hopping transport was sufficient to cause shorting of the gate, while at 2 mol %, charge trapping was observable as transistor threshold voltage shifts (ΔV th). We created three types of devices: with the substituted PS layer as single-layer dielectric, on top of a cross-linked PS layer but in contact with the pentacene (bilayers), and sandwiched between two PS layers in trilayers. Especially large bias stress effects and ΔV th, larger than those in the case of the hexamethoxy and previously studied dimethoxy analogues, were observed in the second case, and the effects increased with the increasing electron-donating properties of the modified side chains. The highest ΔV th was consistent with a majority of the side chains stabilizing the trapped charge. Trilayer devices showed decreased charge storage capability compared to previous work in which we used less donating side chains but in higher concentrations. The ZnO and TCNE modifications resulted in slightly more and less negative ΔV th, respectively, when the side chain polystyrene was not in contact with the pentacene and isolated from the gate electrode. The results indicate a likely maximum combination of molecular charge stabilizing activity and side chain concentration that still allows gate dielectric function.