Lee Seulyi, Jang Mi, Yang Hoichang
Department of Applied Organic Materials Engineering, Inha University , Incheon 402-751, Republic of Korea.
ACS Appl Mater Interfaces. 2014 Nov 26;6(22):20444-51. doi: 10.1021/am506024s. Epub 2014 Nov 4.
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.
通过聚合物接枝法生成的接枝到氧化硅（SiO₂，称为gPS-SiO₂）双层上的聚苯乙烯（PS）被用作有机-氧化物混合栅介质，以制备溶液处理的三乙基甲硅烷基乙炔基蒽二噻吩（TES-ADT）有机场效应晶体管（OFET）。不同分子量（Mw）的PS链的面接枝密度显著改变了介电表面性质，这些PS链的末端带有连接到SiO₂表面的官能化二甲基氯硅烷。较长PS链的较低接枝密度将处理过的SiO₂表面的粗糙度从0.2 nm增加到1.5 nm，水接触角从94°增加到88°。在末端官能化PS的临界Mw以下，SiO₂表面上的gPS链似乎形成了面密度值大于0.1链nm⁻²的刷状构象，但其他高Mw的gPS链形成了盘状结构，其中聚合物层很容易与作为溶质的溶液处理的TES-ADT结合。这些发现表明，低密度的gPS层干扰了TES-ADT在流延膜中的自组装，导致晶粒尺寸和π共轭取向大幅降低。与使用浓度较低的gPS-SiO₂表面制备的TES-ADT OFET相比，SiO₂表面上紧密的gPS链的存在可以产生高电性能，场效应迁移率为2.1 cm² V⁻¹ s⁻¹，阈值电压为-2.0 V，开/关电流比大于10⁷。
