利用電場輔助塗佈增進F8BT薄膜之載子遷移率

Abstract

研究poly((9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo(2,1,3)thiadiazol-4,8-diyl)) (F8BT) 高分子薄膜型態改變對於其光學性質及電荷傳導遷移率的相關性。在光學性質方面，以偏光顯微鏡為主，吸收光譜與螢光光譜為輔；電性方面，以場效電晶體方法量測在水準方向上的電荷傳導遷移率。 本研究中，比較旋轉塗布、滴式塗布與靜態電場滴式塗布三種成膜方法對結構上的影響，而後對薄膜進行退火和淬火處理，使其產生向列型液晶相。在偏光顯微鏡下，只有靜態電場滴式塗布製膜會產生光學異向性，可知在電場作用下，F8BT分子產生有序的結構，而其在熱處理後會形成最顯著的液晶相。由吸收光譜的結果顯示，靜態電場滴式塗布製膜在熱處理後表現出最大的紅位移現象，是因產生顯著液晶相時共軛長度增加最多所致。製作場效電晶體元件，發現只要形成液晶相，皆有相似的電洞遷移率，說明顯著的液晶相對於電荷傳導並沒有太大的助益。比較靜態電場滴式塗布製膜與其退火後形成顯著液晶相的電洞遷移率，兩者也是相似的，故遷移率的結果指出，電場影響下初始的膜形成有序結構與退火後產生有序的液晶相排列，靜態電場可誘導F8BT分子形成有序結構的薄膜，可避免使用退火處理的方法形成向列型液晶相，而達到相同數量級的電洞遷移率。

In this study, the morphology of poly((9,9-di-n-octylfluorenyl-2,7-diyl)-alt- (benzo(2,1,3)thiadiazol-4,8-diyl)) (F8BT) were studied for understanding its effect on optical properties and carrier mobility. The morphology of films was observed by polarized optical microscope (POM) and the actions of molecules were deduced by UV-visible absorption spectra and photoluminescence (PL) spectra. The carrier mobility in horizontal direction was measured by using a field-effect transistor (FET) geometry. Comparison of films prepared from different methods, spin-coating, drop-casting and drop-cast film at presence of a static electric field (E-drop-casting) offered an opportunity to characterize the influence of film morphology on charge transport. The films suffered heat treatments showed a nematic liquid crystalline (LC) phase and kept on through quenching resulting in red-shifted absorption spectra. Only the E-drop-cast film revealed an optical anisotropic phase viewed by POM, implying that F8BT molecules rearranged to an ordered structure under the presence of a static electric field. Furthermore, the E-drop-cast film after annealing came into the most obvious LC phase. Both the E-drop-cast films and the films after heat treatment showed the similar carrier mobility. The results indicated that static electric field could drive F8BT polymer chains to pack with each others and generated ordered structure. The films after annealing also exhibited ordered structure in nematic liquid crystalline phase. These ordered structures enhanced the mobility approximate to one order. The advantage of preparing the film at presence of electric field could not only avoid heat treatment but also raise charge transport mobility.