High-performance Organic Field-Effect Transistors Based on Monodisperse Glassy-Nematic Oligofluorenes

本研究的动机是确定影响单轴取向π共轭体系中空穴迁移率的因素。除了最近报道的单分散性低聚芴，热致液晶芴-噻吩低聚物的合成和表征的空穴迁移率使用场效应晶体管。为了系统地研究链长、分子聚集、取向序参量和场效应晶体管中接触电阻对空穴迁移率的影响，将一系列单分散共轭低聚物及其类似物制备成玻璃-非晶、多畴和单畴玻璃-非晶薄膜，并以七、十二碳二烯为材料制备场效应晶体管，F（Pr）5 F（MB）2和F（MB）10 F（EH）2以及聚芴。空穴迁移率进行了测量的设备，包括单畴和多畴玻璃化薄膜以及玻璃化非晶薄膜。在较低的温度下热退火，低聚芴更容易取向成单畴膜，导致比聚芴更高的R_<abs>。由于几何和能量的无序，双晶非晶薄膜具有最低的迁移率。单畴玻璃-SiO2-F（MB）10 F（EH）2膜的迁移率比玻璃-非晶膜提高800倍。在单畴薄膜中，场效应迁移率值由低聚芴的链长和聚芴的余辉长度决定。对于F（MB）10 F（EH）2，场效应迁移率为0.012 cm^2/Vs，开/关比为1.0×10^4。该迁移率值是相同器件结构中聚芴的两倍。它的结论是，单分散的玻璃基共轭低聚物具有很大的潜力，用于场效应晶体管，因为上级化学纯度，结构的均匀性和规律性，并易于加工成单轴排列的无缺陷的薄膜。

This study was motivated to identify factors affecting hole mobility in uniaxially oriented п-conjugated systems. In addition to the monodisperse oligofluorenes that have been reported recently, thermotropic liquid crystalline fluorene-thiophene oligomers were synthesized and characterized for hole mobility using field-effect transistors. Both series of monodisperse conjugated oligomers and their polymer analogues were prepared into glassy-amorphous, and polydomain and monodomain glassy-nematic films for a systematic study of the effects on hole mobility of chain length, molecular aggregation, orientational order parameter, and the contact resistance in a field-effect transistor.Field-effect transistors were fabricated using hepta- and dodecafluorenes, F(Pr)5F(MB)2 and F(MB)10F(EH)2, and a polyfluorene. Hole mobilities were measured for devices comprising monodomain and polydomain glassy-nematic films as well as glassy-amorphous films. Oligofluorenes were more readily aligned into monodomain films via thermal annealing at a lower temperature, resulting in a higher R_<abs> than polyfluorene. Glassy-amorphous films possess the lowest mobility of all because of the geometric and energetic disorder. The mobility of a monodomain glassy-nematic F(MB)10F(EH)2 film is enhanced over a glassy-amorphous film by a factor of 800. In monodomain films, the field-effect mobility value is determined by the oligofluorene's chain length and the polyfluorene's persistence length. For F(MB)10F(EH)2, the field-effect mobility was evaluated at 0.012 cm^2/Vs with an on/off ratio of 1.0×10^4. This mobility value is twice that of polyfluorene in the same device structure. It is concluded that monodisperse glassy-nematic conjugated oligomers hold great potential for use in field-effect transistors because of superior chemical purity, structural uniformity and regularity, and ease of processing into uniaxially aligned defect-free films.