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

Abstract

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.

2-Aminoanthracene Crystallization in Its Compatible Polystyrene Block: RAFT Synthesis and Enhanced Charge Retention in Pentacene Transistor Gate Dielectrics

“…The Δ V c from charging 5% 2AA in PS was less significant, possibly due to the formation of conductive paths among crystallites. To compare with the previous work, the shift of Δ V c with respect to unit electric field of positive charging was calculated to be about −600 V × (V/nm) −1 for 1% 2AA/PS dielectrics and −180 V × (V/nm) −1 from a previous work of our group, which means that although the magnitude of Δ V c was comparatively small in the present work, the 2AA/PS dielectrics possessed impressive sensitivity to the applied electric field. For 20% PS- b -PAAS blended in PS as dielectrics, the addition of 1% 2AA resulted in a similar behavior as in pure PS except that the Δ V c values for both positive and negative charging were less positive with a smaller magnitude.…”

“…We designed and synthesized the diblock copolymer based on styrene derivatives to fulfill the initial idea to explore how aggregated chargeable side groups function within a pentacene transistor, drawing from our recent experience with polystyrene gate dielectrics. , The synthetic route is shown in Scheme . All of the precursors were synthesized via AIBN-initiated free radical polymerization and RAFT copolymerization.…”