有機半導體之構型設計暨形態調控於光電元件之應用

有機半導體因其具有低成本、質量輕、豐富的分子調控性以及可溶液製程等優勢，於近年受到大量的研究關注與光電應用發展。在其近期的科學研究發掘下，明確的分子結構設計與薄膜形態之特性皆已被證實對於高分子半導體材料無論在光學抑或是電氣特性及元件表現上影響尤為重要。本論文目標在於利用不同分子設計與製程方法開發具本質可拉伸特性之有機半導體材料以及開發新世代有機光驅動記憶體元件，探討其薄膜下物理性質與光電性質之改善，並於有機場效應電晶體與記憶體元件等電子元件之應用進行探討與開發。本論文之第二章至第四章分別介紹與引用不同策略來製備具本質拉伸特性之半導體薄膜改良。於第二章，我們首先利用高分子混摻法作為有效取得彈性高分子薄膜之目的，透過引導具自我排列特性之共軛高分子聚噻吩(P3HT)形成奈米纖維，並將其與高彈性氟化橡膠混合，以藉此經由一系列分析來對此一複合薄膜於拉伸狀態下的形態改變作進一步探討。分析結果顯現，再經由最佳化製程條件下，此一複合薄膜可具有同時提升半導體特性與薄膜機械性質之表現，而此一特色則歸功於分布於彈性橡膠之間的束狀型聚噻吩奈米纖維使之具備優異的耐拉伸特性。除了利用製程方法進行改善外，對於分子結構上的根源設計進行改良亦為相關科研發展的一大主流，在第三章內容中，側鏈基團之設計使高分子在電性表現與薄膜機械性之間具備更為平衡的狀態為主要研究目的。透過合成一系列具不同長度之碳矽烷側鏈(Carbosilane)，分析其薄膜於拉伸狀態下之光學性質與電氣特性之變化，進而利用系統化實驗了解相關側鏈基團設計對於共軛高分子之各項物理性質的影響。分析結果顯現，在全系列具不同側鏈長度之共軛高分子中以具有最長側鏈之PII2T-C10於電氣特性與薄膜機械性質有最佳之平衡表現，其可在兩倍拉伸原長下保有大於1 cm2V-1s-1之優異電氣表現。接著，第四章的部分則透過主鏈構型之序列設計使由共軛高分子聚噻吩(polythiophene)與彈性聚醚類高分子(polyether)組合而成的嵌段型高分子具備不同嵌段序列(如A‒B型、A‒B‒A型、與B‒A‒B型)，以分析主鏈構型不同對於高分子薄膜之電氣特性與機械性質變化。結果顯現所有構型皆具有奈米纖維狀之形態生成，然而又以A‒B‒A型嵌段高分子具有最為吸引人之表現，在光學顯微鏡觀察薄膜變化之分析中，可以明確發現A‒B‒A型嵌段高分子可於近乎兩倍拉伸原長下保持平滑不具裂痕之表現，在整合製備成全拉伸式阻抗型記憶體元件後，該元件亦可在重複拉伸之激烈操作下保持穩定之讀寫功能與優異快閃記憶體表現(FLASH memory)。最後，以光訊號作為開關之新式光記憶體元件為近期新興發展之熱門研究課題之一，在第五章及第六章我們則分別利用不同的有機駐集極(electret)設計，使新開發之光應答記憶體能有效改善其反應效能與功能性。在第五章利用的是具自組裝特性之硬桿‒柔軟嵌段分子，透過記憶體層與傳輸層之共軛核心搭配，在無論採用的是p型或是n型之半導體下，該元件皆能具有快速開關及高對流對比表現，而相匹配的共軛核心更提供該半導體元件近乎零能障阻礙，使之能於極低的操作電壓(0.1V)下進行讀寫。第六章部分採用的是複合奈米材料做為雙光感式浮動閘極，我們透過光感奈米粒子與包覆高分子之吸收波段互補特性，使得製備之光記憶體元件能具有可見光啟動、紫外光抹除之記憶體特性，於此同時保有穩定的記憶體開關及良好長期記憶特性。此二章節研究具有給予未來相關光通訊技術元件與神經元元件之研究更多可能性與更大之開發潛能。

關鍵字

共軛高分子；形態學；分子構型；可拉伸半導體；光感式記憶體元件

並列摘要

The rapid development on organic-based semiconducting materials have gained much scientific interest because of their superior features of lower cost, light weight, molecular flexibility, and solution processability for opto-electronic devices. The exploration of structural and morphological properties in such π-conjugated materials offer an essential insight for achieving better optical and electrical properties as well as device performance. The goal of this thesis is to employ several effective strategies for wearable electronics using polymeric semiconductors and next-generation photonic memory device using organic electrets, as described in the following: In Chapter 2, P3HT nanowires and fluorine rubber was employed as a stretchable active layer with a hole mobility higher than that of pristine P3HT with a capability to sustain the electrical properties under a high strain. It suggests that a suitable phase separation that could give both enhancements on charge transporting and film stretchability simultaneously. Next, a rational design using molecular engineering on intrinsically stretchable semiconductors are described in Chapters 3-4. The carbosilane side chains incorporated isoindigo-bithiophene based polymeric semiconductors were designed and studied. It was found that the systematically tailoring the length and branch position on side-chains offered an effective route to optimize charge-transport behavior and improve the mechanical properties of the films. Among them, PII2T-C10 polymer possess a most desired performance that maintained a mobility over 1 cm2V-1s-1 under a 100% strain level. Next, block copolymers (BCP) with different conjugated/elastic sequence using P3HT and polyether blocks were explored using different polymer architecture including AB-type, ABA-type, and BAB-type. A clear self-assembled fibrillary nanostructure happened to both BCPs while only the ABA-type BCP remained perfectly smooth film that could bear up to 100% strain without yielding any cracks. A fully stretchable resistor-type memory device using such BCP film was fulfilled with a stable FLASH memory behavior that preserved an excellent current contrast even after 500 stretching/releasing cycles. Last, newly developing memory device using light as switch was explored using the electrets of conjugated rod-coil materials or hybrid nanocomposites, as detailed in Chapters 5-6. By using the same conjugated rod in both the electret and transporting layer, both n-type and p-type memory device exhibited a fast response between ‘‘Photo-On’’ and ‘‘Electrical-Off’’ bistable states over 100000, with an extremely low programing driving force of 0.1V is achieved. Next, hybrid nanocomposites using perovskite quantum dots and insulating polymers with conjugated side-chains were used as double photo-active floating gate. By using such hybrid nanocomposite as the electret, a fully optically switchable memory device could be produced with visible and UV-lights, which gave a stable operating performance of on/off ratio up to 10000 and excellent retention times. The above results could be further extended for the future development on photo-responsive opto-electronics such as light-recorder and synaptic device, and smart artificial vision system.

並列關鍵字

conjugated polymers ； morphology ； molecular architecture ； stretchable semiconductor ； photonic memory device

參考文獻

1. H. Sirringhaus, P. J. Brown, R.H. Friend, M. M. Nielsen, K. Bechgaard, B. M. W. Langeveld-Voss, A. J. Janssen, E. W. Meijer, P. Herwig and D. M. de Leeuw, Nature, 1999, 401, 685.