具液晶玻璃態及非晶態有機半導體之双極性載子傳輸特性研究

Abstract

由於有機材料具有許多有趣的光電特性與應用，因此在近二十年受到相當廣泛的研究。而在有機光電元件中，載子傳輸能力為影響元件特性之重要因素，因此如何提高載子遷移率及發展双極性載子傳輸材料是相當重要的研究方向。在本論文中，我們使用飛行時間量測技術探討有機材料中的載子特性。 我們研究具有液晶相的有機半導體，四聚芴化物(Tetrafluorene)之載子傳輸特性。透過在液晶相對其做分子的配向排列，發現可將材料的載子傳輸率較非晶態薄膜之值提高約一百倍。此外，為了更進一步了解不同的分子排列對載子傳輸機制的影響，我們進行了變溫/變電場的量測，並應用不同之電荷傳輸模型來解釋量測中所發現的一些趨勢。 最後，我們研究一系列具有高量子效率及藍光發光特性之苯並咪唑(Benzimidazole)/芳香胺(arylamiine)化合物，亦發現這些材料具有有趣之双極性載子傳輸特性。

Organic semiconductors have attracted a great deal of attention in the last two decades because they exhibit a variety of interesting optical, electrical, and optoelectronic properties. In the applications of organic optoelectronics, charge transport ability plays an important role in the device performance. Therefore, the enhancement of carrier mobility and the development of bipolar carrier transport materials are important. In this thesis, we use the time-of-flight technique to investigate carrier transport properties of organic materials. In the first part of the works, we studied the charge-transport properties of a tetrafluorene which exhibit the liquid crystal (LC) mesophase at high temperature and the glass phase at room temperature. By mesophase-mediated alignment, the carrier mobilities in the aligned LC glass of tetrafluorene are enhanced approximately by two orders of magnitude, compared to those in amorphous film. To understand the influences of molecular arrangement on detailed mechanisms of carrier transport in tetrafluorene, we also investigated the temperature and field dependence of charge transport and analyzed them with existed charge-transport models. Finally, we investigate the charge-transport properties of a class of high-quantum-yield blue-emitting compounds containing benzimidazole and arylamines moieties. It is found that these compounds exhibit interesting bipolar carrier-transport properties in the amorphous phase.