本論文以高分子poly(2,5-bis(3-alkylthiophen-2-yl)thieno〔3,2-b〕thiophene) (PBTTT-C14)製作有機薄膜電晶體的載子傳輸層薄膜，將PBTTT-C14分別使用旋塗製程與熱梯度結晶製程製作有機薄膜電晶體元件，並探討兩種薄膜的分子結晶特性對元件的電特性影響。研究分為兩部分，第一部分將探討PBTTT-C14以不同製程製作薄膜，比較兩者的物性與電性參數之差異；第二部分則是將熱梯度結晶製程製作的薄膜電晶體應用在線偏振光感測，觀察元件在不同偏振光照射下元件電流造成的光響應變化。
物性分析的部份，我們用偏光顯微鏡(POM)、原子力顯微鏡(AFM)與穿透式電子顯微鏡(TEM)觀察PBTTT-C14薄膜的表面形貌。當我們旋轉POM載台，POM的目鏡能觀察到熱梯度結晶薄膜有亮暗變化，表示PBTTT-C14分子具有方向性；AFM和TEM觀察到熱梯度結晶薄膜表面的PBTTT-C14分子具有方向性，而旋塗薄膜表面的PBTTT-C14分子則是顆粒狀雜亂分佈。X-光繞射(XRD)分析與紫外光/可見光光譜儀分析能分辨薄膜的結晶程度，熱梯度結晶薄膜在XRD結果的(100)、(200)、(300)之訊號皆有較小的半高寬，表示熱梯度結晶薄膜有較好的結晶；而吸收光譜在580 nm波段代表PBTTT-C14薄膜的結晶區，熱梯度結晶薄膜在此波段有明顯的波峰，旋塗薄膜則是趨近平緩。電性分析的部分，熱梯度結晶元件作為實驗組、以旋塗元件作為對照組進行量測。由結果顯示，當熱梯度結晶薄膜作為載子傳輸層，元件有較好的載子遷移率、次臨界擺幅、電流開關比與較低的臨界電壓。此外，本研究對熱梯度結晶薄膜使用四種不同熱退火溫度，發現以130度退火30分鐘再以80度退火一小時有最好的物性與電性。
應用的部分，將PBTTT-C14製作的元件應用在線偏振光感測，熱梯度結晶元件的載子傳輸層薄膜具有方向性，當偏振光以不同方向線偏振照射在主動層薄膜時激發出的激子(exciton)量不同，以致量測汲極電流的差異隨時間變化將近兩倍；當不同線偏振光照射在旋塗元件時，汲極電流隨時間變化幾乎沒有差異。

The growth of organic semiconductor influences the crystalline and polycrystalline microstructures, which greatly affect the performances of related organic thin-film transistors (OTFTs). Accordingly, the investigation is very significant to correlate the crystallite properties of organic semiconductor with the charge transport in OTFTs. In this study, p-type OTFTs were fabricated using poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14) as active materials. We demonstrated a method of thermal gradient to guide the orientation of PBTTT-C14 molecules during the formation of PBTTT-C14 film, resulting in an ordered PBTTT-C14 crystallization. To guide the growth of PBTTT-C14 films on dielectric surface, the hexamethylbenzene (HMB) was used to assist the crystallization of PBTTT-C14 during the formation of PBTTT-C14 films denoted HMB-processed (H-P) PBTTT-C14 films.
To realize the crystalline orientation of H-P PBTTT-C14 films, the polarizing optical microscope (POM) was used to measure H-P and spin-coating PBTTT-C14 films. By observing different angles of H-P films from 0o parallel to the direction of thermal gradient to 45o, we found that the POM image was completely dark at 0o and the brightest at 45o. The crystallite and surface topography of H-P PBTTT-C14 films were measured by the transmission electron microscopy (TEM) and atomic force microscope (AFM), respectively. The images show that the H-P films have crossover crystallizations and ordered orientation along the direction of thermal gradient. In addition, we also applied x-ray diffractometer (XRD) and ultraviolet/visible spectrophotometer (UV/Vis) to study the orientation of H-P PBTTT film. The electrical properties of H-P PBTTT-C14-based OTFTs were obtained by using Keithley 4200SCS semiconductor analyzer. Based on the electrical properties of OTFTs, the results indicate that the mobility of carrier, subthreshold swing, threshold voltage, and on/off current ratio of H-P OTFTs were better than the device with spin-coating PBTTT-C14. In summary, we demonstrated a simple method to enhance the performances of polymer-based OTFTs by improving the microstructure of PBTTT-C14. This novel crystalized technique has potential to enhance the performances and broaden the applications in other organic devices.

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