| 摘要: | 有機半導體材料基於可溶液製程、低溫製程、成本低廉以及分子可設計等優點，這 些優點利於大面積塗佈並應用於可撓式顯示器、感應器、電晶體、太陽能電池等軟性電 子元件，因此本論文分為三個部分深入探討有機材料之分子設計以及其混摻系統應用於 電子元件。
第一部分以含硫族側鏈之聯噻吩 (XBT) 為核心設計高效能 P 型有機小分子材料應 用於場效應電晶體，探討引入不同側鏈長度 (R = C14，C10，C6)、調整末端基並環數目 (並三噻吩 (dithienothiophene; DTT)，並二噻吩 (thienothiophene; TT)，噻吩 (thiophene; T))以及引入側鏈基團 (–XR，X = Se，S，O) 之影響。利用側鏈長度的不同改善薄膜的 連續性及增加溶解度，增加末端基的並環數可以改善共軛長度，並探討主鏈噻吩環之硫 原子與側鏈氧、硫以及硒之分子內作用力所形成的分子內鎖 (intramolecularlock)。從單 晶結果可得，Se (側鏈)∙∙∙S (噻吩) 距離小於原本凡得瓦半徑總和，具有最強非共價鍵作 用力，聯噻吩藉由側鏈之影響形成極高的分子共平面性，當利用剪切力塗佈法製作有機 場效應電晶體元件時，DDTT-SeBT-C14 (1) 最高電洞遷移率可高達 4.01 cm^2 V^–1 s^–1，此結 果是歷年期刊發表以噻吩為核心的有機小分子材料之最高電洞遷移率，並透過晶體學、 薄膜形態以及微結構進行更深入的探討。
第二部份以含硫醚側鏈之並三噻吩 (DSDTT) 為核心，末端基的兩端各加入並三噻 吩，合成出新 DDTT-DSDTT 有機小分子半導體材料，藉由硫醚側鏈的硫原子與主鏈噻 吩環內硫原子間之分子內作用力形成的分子內鎖，因此具有較佳的共平面結構，由於導 入硫醚側鏈，使其具有良好的溶解度且易溶於常用有機溶劑。在溶液製程條件調控上， 利用對於環境較友善的苯甲醚溶劑並透過剪切力塗佈法製作有機半導體薄膜，將其應用 於有機場效應電晶體元件上，其最高電洞遷移率可達 3.19 cm^2 V^–1 s^–1。此外，利用有機小分子DDTT-DSDTT與絕緣高分子聚α-甲基苯乙烯 (PαMS) 混摻後亦可維持高電性效能，經過溶液製程後有明顯的垂直相分離且仍維持有機小分子之高結晶度。在 DDTT- DSDTT 重量百分比為 50%時，PαMS 垂直相分離於下層有利於上層 DDTT-DSDTT 形成 更好的分子排列，其最高電洞遷移率仍可維持在 2.44 cm^2 V^–1 s^–1，在電偏壓應力測試時， 保有較小的閾值電壓位移 (threshold voltage shift) 且於大氣環境下有較佳的穩定性。
第三部分利用溶液製程法將 n 型商用共軛高分子 N2200 與具有高遷移率之醌型噻 吩並異靛藍 TIIQ，運用混摻技術製作高光響應之光電晶體。利用不同混摻比例調節光電 晶體之性能，在紅光 (680nm) 照光下其 88%混摻光電晶體元件之最高光響應 (photoresponse) 可達到 4065 AW^–1 且特定光偵測性 (photodetectivity) 為 1.4 × 10^13 Jones，在混摻半導體層中，仍保有極高遷移率 1.59 cm^2 V^–1 s^–1，由於加入有機小分子於 混摻系統中有助於紅光之吸收，因此可有效的光生載子拆解以及傳遞，因此，此有機半 導體混摻之技術成功開發高光響應之有機光電晶體。;Organic semiconductors have the advantages of low temperature process, low cost, good ductility, and molecular design, which are favorable for large area coating and can be applied on flexible electronic application such as flexible displays, sensors, transistors, and solar cells. Therefore, this dissertation is focusing on the study of the molecular design and blending system of organic materials for electronic application and it will be divided into three parts.
First, the high-performance P-type organic small molecule semiconductors with a core of heteroalkyl-substitution dithiophene (XBT) have been designed for organic field effect transistors (OFETs). The core of SeBT has investigated the effects of introducing different side chain lengths (R = C14, C10, C6) and end-functionalization with two dithienothiophene (DTT), thienothiophene (TT), and thiophene (T) units. Moreover, the core XBT is also explored the impact of the chalcogen heteroatom (–XR, X = Se, S, O), which is developed selenotetradecyl SeBTs, thiotetradecyl SBTs, and tetradecyloxy OBT. Side chain lengths are able to improve the film continuity and tuning the solubility. Increasing the number of aromatic rings can improve the conjugation length. The impacts of the chalcogen heteroatom obtain the noncovalent conformational lock with the sulfur in the aromatic ring. From the single crystal data, the SeBT small molecule obtain a torsion angle of ~ 0° as well as coplanar backbone. When organic field effect transistors are fabricated by a solution sheared process, the highest hole mobility of DDTT-SeBT-C14 (1) can reach 4.01 cm^2 V^–1 s^–1 which is the best hole mobility value reported to date for fused-thiophene-based small molecules. In addition, these results are also investigated by crystallography, thin film morphology, and microstructure analysis.
In second research, the core of dithiooctyl dithienothiophene with end functionalized fused dithienothiophene (DTT) units, named DDTT-DSDTT, was synthesized and characterized for OFETs. The intramolecular lock with S (alkyl)∙∙∙S (thiophene) interaction bring out a better coplanar structure, resulting in better solubility in the anisole as a green solvent. Therefore, utilizing a solution-sheared processing method to fabricate the active layer for OFETs. The DDTT-DSDTT compound exhibits highest mobility of 3.19 cm^2 V^–1 s^–1. Moreover, the small molecule DDTT-DSDTT and insulting polymer poly(α-methylstyrene) (PαMS) blend films could maintain high performance causing by vertical phase separation with PαMS layer between DDTT-DSDTT layer and dielectric layer. The 50 wt% DDTT-DSDTT blend thin film show high mobility of 2.44 cm^2 V^–1 s^–1 which exhibit high crystallinity and better molecular packing. The blend devices show good air stability and also a smaller threshold voltage shift under gate bias stress.
In third research, solution processable organic phototransistors are reported by the heterojunction composition with different weight ratio of N2200 polymer/ quinoidal thienoisoindigo (TII)-containing small molecule as the semiconductor layer under the various incident red light intensities (680 nm). The blend system of phototransistor shows high photoresponse of 4064 AW–1, detectivity of 1.4 × 10^13 Jones, and high mobility of 1.59 cm^2 V^–1 s^–1. The reason that introduction of TIIQ small molecule is able to improve the absorption of red light, photogenerated carriers, and fast charge carriers. These results show the blending strategy of semiconductor offer successfully developing for organic phototransistor. |
