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

本研究旨在确定影响单轴取向п共轭体系空穴迁移率的因素。除了最近报道的单分散低聚荧烯外，还合成了热致液晶茂并用场效应晶体管对其空穴迁移率进行了表征。为了系统地研究链长、分子聚集、取向有序参数和接触电阻等因素对空穴迁移率的影响，将系列单分散共轭低聚物及其聚合物类似物制备成玻璃无定形、多磁区和单磁区玻璃向列相薄膜，以F(Pr)5F(MB)2和F(MB)10F(EH)2和聚荧烯为原料制备了场效应晶体管。测量了由单磁区和多磁区玻璃向列相薄膜以及非晶玻璃薄膜组成的器件的空穴迁移率。低聚荧烯在较低的温度下通过热退火更容易取向成单畴薄膜，导致比多荧烯更高的R&lt；abs&gt；。由于几何无序和能量无序，非晶态玻璃薄膜具有最低的迁移率。单畴玻璃向列相F(MB)10F(EH)2薄膜的迁移率比非晶玻璃薄膜提高了800倍。在单区薄膜中，场效应迁移率的大小取决于低聚荧烯的链长和聚荧烯的存留长度。对于F(MB)10F(EH)2，场效应迁移率为0.012 cm~2/vs，开关比为1×10~(-4)，该迁移率是相同器件结构下聚荧烯的两倍。结果表明，单分散玻璃向列型共轭低聚物具有良好的化学纯度、结构均一性和规整性，易于加工成无缺陷的单轴取向薄膜，在场效应晶体管中具有很大的应用潜力。

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.