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

다국어 초록 (Multilingual Abstract)

<P>Polystyrene (PS) grafted to silicon oxide (SiO<SUB>2</SUB>, referred to as <I>g</I>PS-SiO<SUB>2</SUB>) 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 (<I>M</I><SUB>w</SUB>) PS chains with end-functionalized dimethylchlorosilane attached to the SiO<SUB>2</SUB> surfaces. Lesser grafting densities of longer PS chains increased the surface roughness of the treated SiO<SUB>2</SUB> surfaces from 0.2 to 1.5 nm, as well as the water contact angles from 94° to 88°. Below a critical <I>M</I><SUB>w</SUB> of end-functionalized PS, the <I>g</I>PS chains on the SiO<SUB>2</SUB> surfaces appeared to form a brush-like conformation with an areal density value greater than 0.1 chains nm<SUP>–2</SUP>, but other high-<I>M</I><SUB>w</SUB> <I>g</I>PS 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 <I>g</I>PS 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 <I>g</I>PS chains on the SiO<SUB>2</SUB> surface could yield high electrical performance of TES-ADT OFETs with a field-effect mobility of 2.1 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>, threshold voltage of −2.0 V, and on/off current ratio of greater than 10<SUP>7</SUP> when compared to those developed using less-concentrated <I>g</I>PS-SiO<SUB>2</SUB> surfaces.</P><P><B>Graphic Abstract</B>
<IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-22/am506024s/production/images/medium/am-2014-06024s_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am506024s'>ACS Electronic Supporting Info</A></P>