本論文以?型為主要結構之n型小分子作為有機半導體材料，並以可溶液製程法之剪切力塗佈法製備具有單一方向性與高結晶性之有機場效應電晶體。一系列以環戊烷二?吩 (cyclopentadithiophene)為核心之?型 (quinoidal) n型小分子CSRCDTQ，發展出以碳-碳雙鍵作為起點並接上不同側鏈長度之硫碳鏈 (alkylthio)，並以三種小分子材料(CSRCDT8Q、CSRCDT10Q及CSRCDT12Q分別為硫原子後接上8個、10個及12個碳之側鏈)，藉由硫-硫元素相互作用力來增強分子之共平面性，並利用密度泛函計算佐證。探討有機場效應電晶體之電荷傳輸與薄膜微結構以及分子堆疊排列三者間之關係。改變側鏈長度對於元件效能、分子排列以及結晶性產生之影響，將利用光學顯微鏡、紫外光-可見光光譜儀、原子力顯微鏡以及低掠角廣角X光繞射來分析。CSRCDT12Q具有最長之側鏈長度，故溶解性最佳，其薄膜具有高結晶性、最短π-π堆疊距離(3.43 ?)以及連續之特性、晶粒較大且分子排列為有利於電荷傳輸之單一方向排列，因此達到最高垂直方向之電子遷移率 (μe)為0.14 cm2 V-1 s-1以及平行方向之電子遷移率為 0.08 cm2 V-1 s-1、電流開關比 (ION/IOFF)超過103。CSRCDT10Q亦具備高結晶性、晶粒最大且分子排列為單一方向，但由於溶解性沒有前者好，且π-π堆疊距離為3.47 ?導致度垂直方向電子遷移率較低，為0.09 cm2 V-1 s-1而平行方向之電子遷移率為0.05 cm2 V-1 s-1、電流開關比亦超過103。最後CSRCDT8Q為最短側鏈之分子，其溶解性較差，雖然仍具有單一方向分子排列之特性，但其晶粒尺寸小於前面兩者，π-π堆疊距離為3.49 ?，因此不利於電荷傳輸，垂直方向電子遷移率為0.025 cm2 V-1 s-1、平行方向之電子遷移率為 0.018 cm2 V-1 s-1，可藉由垂直方向以及平行方向電子遷移率之比較，得知元件具備異向性 (anisotropy)之特性。同時CSRCDTQ系列存放於濕度控制於30~40 %之大氣環境下一個月，仍維持良好的空氣穩定度。結果證實，以碳-碳雙鍵作為起點並接上不同側鏈長度之硫碳鏈於環戊烷二?吩有助於調控分子堆疊以及提高溶解度，從而提高有機場效應電晶體之電子遷移率。;Three quinoidal bis(alkylthio)methylene-cyclopentadithiophene (CSRCDTQ) small molecule compounds with dicyanomethylene end?capping units and octylthio/ decylthio/dodecylthio side chains were synthesized as n?type organic semiconductors for solution?processable organic field effect transistors (OFETs). The planar CDT core with methylene group at side chains as starting points improves the backbone stacking due to the effect from less free rotation of the side chain linkage. The sulfur?sulfur chalcogen interactions extend the molecular coplanarity with strong interchain packing, which is confirmed by density functional calculations. The top contact bottom gate (TC / BG) device architectures of OFETs were fabricated with the solution-sheared organic semiconductor layer. The effect of changing the side chain length on device performance, molecular packing and crystallinity were studied by using the polarized optical microscopy (POM), UV-vis spectroscopy, atomic force microscope (AFM) and grazing-incidence X-ray diffraction (GIXRD). OFETs based on solution-sheared CSRCDT8Q, CSRCDT10Q and CSRCDT12Q exhibit the electron mobility of up to 0.025, 0.09 and 0.14 cm2 V-1 s-1 in the perpendicular direction and up to 0.018, 0.05, 0.08 cm2 V-1 s-1 in the parallel direction with current ON/OFF ratio (ION/IOFF) of 103-105. Due to poor solubility and cracks in the films, the mobility of CSRCDT8Q and CSRCDT10Q are lower. The different direction of electron mobility demonstrates the anisotropy in CSRCDTQ films fabricated by the solution-sheared process. The CSRCDTQ films are stored in an atmospheric environment with a humidity controlled at 30-40% for one month, and still maintain good air stability. The result confirms that side chain length of bis(alkylthio)methylene can help for tuning molecular packing and improving solubility to enable the improved charge transport mobility of solution-processed OFETs.
