MEHPPV元件中之電荷傳導異向性

Abstract

以時間解析電激發光和場效應電晶體方法可分別量測得MEHPPV的垂直方向與平行方向之電洞載子遷移率。高分子薄膜之光學性質與型態的研究則可了解光學性質與型態上的效應對於電荷傳導的影響。在本研究中，MEHPPV 高分子分別以氯苯、甲苯當作溶劑配製成導電高分子溶液並且製成薄膜與元件。實驗結果顯示高分子薄膜的光學性質相似但卻有不同的電洞遷移率。此外，垂直方向與平行方向的載子遷移率明顯地有著差異。更近一步地實驗結果又發現使用不同的溶劑會對共軛高分子產生型態上的影響。經由光散射可知，以氯苯高分子溶液旋轉塗布所製成之薄膜比以甲苯溶液旋轉塗布製成之薄膜有較明顯的層狀結構。將型態效應與垂直、水平方向的電洞遷移率做比較後可知，電荷傳導異向性是因來自不同溶劑對MEHPPV高分子薄膜形成了不同程度的層狀結構所導致。令人驚訝的是如此結構上的異向性與載子遷移率的異向性竟然不謀而合。這樣的結果應起因於電洞載子在水平方向上的高密度電子層狀區域具有較佳的載子遷移率。

The hole mobility in vertical and horizontal directions were measured by means of time-resolved or transient electroluminescence (TrEL) and field-effect transistor (FET) methods for poly(2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV). The optical properties and morphology were studied for understanding the optical and morphological effects on charge transport properties. MEH-PPV films prepared from chlorobenzene (CB) and toluene (TL) were used and fabricated into devices in this work. The results indicted the optical properties are identical but different in hole mobility. In addition, the charge mobility shows obvious difference in vertical and horizontal direction. Further, the morphological effect in conjugated polymer films was induced by using different solvents. Through scattering measurements, the solvent induced layered structure within polymer films spun from chlorobenzene (CB) solution is more predominant, however, the films spun from toluene (TL) solution show weak layered feature. Comparing morphological effects with the hole transporting results measured by thin film transistor device (horizontal direction) and polymer light emitting diode (PLED) based time resolved electroluminescence method (vertical direction), charge transport anisotropy was observed as a result of the layered structure in the conjugated polymer. Amazingly, this structural anisotropy corresponds with the mobility anisotropy and it is believed to be consistent with hole carriers owning greater mobility in the regions of high electron density which is parallel to the substrate.