苝分子晶體陣列-結晶多型態對有機場效電晶體性能的影響

Abstract

利用濕式製程將有機共軛分子形成具有取向性的晶體陣列已經被廣泛的研究，然而大多數的研究都致力於有效地控制晶體取向性與覆蓋率，卻很少對晶格結構進一步控制與討論，晶格結構對有機場效電晶體的元件表現是有一定程度的影響。尤其大部分的有機共軛分子在形成固態結構時通常都有結晶多型態的現象，也就是說分子會形成不只一種固態結晶結構。因此，在不同結晶結構下，載子在分子間傳遞時必定有不同的影響，故研究濕式製程之晶體陣列中結晶多型態對於載子遷移率的影響是重要的。 此外，先前的文獻指出苝分子具有α相和β相兩種結晶多型態，且在理論計算的研究中指出具有高的載子遷移率，所以苝分子確實提供我們探討結晶多型態的研究平台，但在許多情況下兩相會一起產生，因此嚴重影響了載子遷移率，目前以真空蒸鍍法製程載子遷移率只有10-7~10-4 cm2V-1s-1。 在此研究利用控制溶劑選擇、溶液濃度與成核溫度，對於形貌與結晶多型態進行討論，且探討苝分子結晶多型態對元件表現的影響，並用螢光顯微鏡與電子繞射對於晶格結構的判定，可發現利用濕式製程以四氫呋喃為溶劑在較高溫且較高濃度下可形成α相晶體陣列；而在較低溫且較低濃度下可形成β相晶體陣列，最後分別量測α相和β相的晶體陣列的元件表現，結果分別為µh= 0.015 cm2/Vs 和µh= 0.11 cm2/Vs，因此本論文成功解釋控制結晶多型態在提升電晶體元件表現上的重要性。

Solution-processed crystal arrays of π-conjugated molecules have become the essential component in the organic field-effect transistors (OFETs). However, the current procedures only facilitate the control of the crystal orientation, but lack the ability to adjust the lattice structure with the crystal arrays. Most conjugated molecules from polymorphic lattice structures which have different mobility limits. Knowing the mechanism of crystal polymorphism form in the solution processed crystal arrays provides the potential to further optimize the performance of the conjugated molecules. Perylene is a typical polycyclic aromatic hydrocarbon, having two polymorphs known as α-phase and β-phase. Then α-phase (sandwich-herringbone) and β-phase (herringbone) grow simultaneously under various conditions. In addition, the μhole values for the β-phase and α-phase of perylene are calculated as 23.4 cm2/Vs and 8.3 cm2/Vs, respectively. Thus the perylene crystals promote to research the impact of polymorphisms in charge transport. In this study, the morphologies and phase selectivity are sensitive to solvent choice, solute concentration and growth temperature. Thus preparing the solution processed perylene crystal arrays in the different conditions to study the mobility for the certain phases is important. Using the results of Fluorescence microscope and electron diffraction can identify the polymorphs of perylene crystals. In this device, the hole mobility of 1.5×10-2 cm2/Vs and 0.11 cm2/Vs are obtained for the most of α-phase perylene crystal arrays and the β-phase perylene crystal arrays by the solution-processed, so the mobility of certain phases is worthy of study.