Optimized Grafting Density of End-Functionalized Polymers to Polar Dielectric Surfaces for Solution-Processed Organic Field-Effect Transistors

Abstract

Polystyrene (PS) grafted to silicon oxide (SiO2, referred to as gPS-SiO2) bilayers generated via a polymer grafting method were used as organic-oxide hybrid gate dielectrics to fabricate solution-processed triethylsilylethynyl anthradithiophene (TES-ADT) organic field-effect transistors (OFETs). The dielectric surface properties were significantly altered by the areal grafting densities of different molecular weight (Mw) PS chains with end-functionalized dimethylchlorosilane attached to the SiO2 surfaces. Lesser grafting densities of longer PS chains increased the surface roughness of the treated SiO2 surfaces from 0.2 to 1.5 nm, as well as the water contact angles from 94° to 88°. Below a critical Mw of end-functionalized PS, the gPS chains on the SiO2 surfaces appeared to form a brush-like conformation with an areal density value greater than 0.1 chains nm(-2), but other high-Mw gPS chains formed pancake structures in which the polymeric layers were easily incorporated with solution-processed TES-ADT as a solute. These findings indicate that low-density gPS layers interfered with the self-assembly of TES-ADT in cast films, causing great decreases in crystal grain size and π-conjugated orientation. The presence of compact gPS chains on the SiO2 surface could yield high electrical performance of TES-ADT OFETs with a field-effect mobility of 2.1 cm2 V(-1) s(-1), threshold voltage of -2.0 V, and on/off current ratio of greater than 10(7) when compared to those developed using less-concentrated gPS-SiO2 surfaces.

Novel Eco‐Friendly Starch Paper for Use in Flexible, Transparent, and Disposable Organic Electronics

“…The surface roughness of the dielectric layer played a significant role in the formation of a crystalline semiconducting layer structure. A rough dielectric surface can prevent the surface diffusion of deposited semiconductor molecules, thereby resulting in smaller grains and less crystalline structures in the semiconductor layer . As shown in the AFM images of the pentacene and DNTT films grown on the parylene‐C dielectric, in Figure d,e, the grains were 100–200 nm in size, much smaller than the grain sizes (higher than 1 µm) in pentacene and DNTT grown on a smooth dielectric surface, such as a spin‐coated polymer or silane‐treated SiO x dielectrics.…”

Recent Advances in the Synthesis of Polymer-Grafted Low-K and High-K Nanoparticles for Dielectric and Electronic Applications

“…The lower molecular weight PS- g -SiO 2 surface exhibited smoother brush like structure while higher molecular weight PS- g -SiO 2 surface exhibited pancake like structure. The smoother surface of 8 kDa PS- g -SiO 2 surface showed the highest mobility (2.12 cm 2 ·V −1 ·s −1 ) whereas the pancake surface of 135 kDa PS- g -SiO 2 showed the lowest mobility (0.85 cm 2 ·V −1 ·s −1 ) [ 219 ].…”

Surface-grafting polymers: from chemistry to organic electronics

“…They studied grafting densities of different molecular weight (M w ) PS, finding that high-M w polymers lead to lower grafting densities. 10 In their work, the SiO 2 surface was modified by different molecular weight (M w ) PS chains with end-functionalized dimethylchlorosilane chemically attached to the surfaces. The density of the PS chains grafted onto the surface significantly influenced the assembly of triethylsilylethynyl anthradithiophene (TES-ADT) molecules on the substrate.…”

“…[5][6][7][8][9] The characteristics of the grafting polymer film can be accurately modulated at the micro/ nano-scale by facile physical or chemical methods. [10][11][12] Thus, surface-grafting technology, a simple and efficient method to fine-tune physical/chemical properties or functionality for material interface science, has been rapidly developed in various fields relating to surface/interface science, such as optoelectronics, 13,14 energy, 15,16 biomedical science 17,18 and so on.…”

“…(c) Schematic diagram of TES-ADT OFETs. (d and e) Transfer curves and (f) output curves at different M w gPS layers 10. Copyright 2014, American Chemical Society.…”