有機發光二極體(OLEDs)是藉由電子、電洞在發光層相遇，再結合而產生發光，因此電子、電洞傳輸速率之平衡對發光效率有很大的影響。Alq3為一常見的OLEDs綠光材料，因其有高的量子效率，常做為發光層，此外，Alq3也具有好的電子傳輸特性，亦為常見的電子傳輸材料。但其電洞注入有較大的能障(0.7 eV)，為了提升電洞注入，常在陽極和Alq3間加入電洞傳輸層，目前最常見的電洞傳輸層為NPB，但NPB只能用真空蒸鍍的方式成膜，耗費成本，故開發可用濕式製程成膜的電洞傳輸材料將有利元件製作及降低成本。本研究以Wittig reaction合成以芴(fluorene)為核心，carbazole為末端基之化合物(FC)，並且以紅外光譜(FT-IR)、核磁共振光譜(1H-NMR、COSY、NOESY)、質譜儀(MS)、元素分析儀(EA)鑑定其結構，並探討其熱性質、電化學性質、光學性質及表面成膜性質，最後製備多層電激發光元件探討其發光特性。
FC分子以芴為核心，並經由Wittig reaction產生共軛鍵，其結構不對稱且碳4位置上的carbazole和芴平面之間形成不共平面的扭角，阻礙分子堆疊，使得FC有玻璃轉移溫度(62 oC)，但沒有明顯的熔點和結晶溫度。薄膜態UV/Vis最大吸收和螢光光譜(PL)最大放光分別為409 nm和454 nm，FC分子結構具有carbazole基團，能有效提升其HOMO能階(-5.21 eV)，降低電洞由PEDOT:PSS注入能障。FC (Mw = 1160.7)可利用簡易旋轉塗佈的方式製備均勻薄膜，薄膜表面的粗糙度(rms roughness = 0.96 nm)和傳統電洞傳輸材料NPB相當。FC作為電洞傳輸層元件結構為[ITO/PEDOT:PSS/HTL(25 nm)/Alq3(50 nm)/LiF (0.5 nm)/Al (100 nm)]最大亮度和最大電流效率分別為21400 cd/m2、3.20 cd/A，CIE 1931色度座標為(0.30, 0.55)，電流效率高於以NPB為電洞傳輸層之元件效率(2.58 cd/A)。研究結果顯示，FC具發光及電洞傳輸功能，且可以溼式塗佈方式加工，具有光電材料應用的潛力。

An efficient trifunctional hole-transporting material 2,4,7-tri[2-(9-hexylcarbazole)ethenyl]-9,9-dihexylfluorene (FC), containing fluorene core and terminal carbazoles, has been synthesized by Wittig reaction. The FC has been fully characterized using FT-IR, 1H-NMR, mass spectrometry, elemental analysis, DSC, optical spectra, cyclic voltammetry, and AFM. Finally, it was employed as hole-transporting layer (HTL) to fabricate OLEDs to evaluate its potential application in optoelectronic devices.
From the DSC analysis, the glass transition temperature (Tg) of FC was observed at 62 ℃, but no obvious Tm and Tc was detected. The asymmetric structure of FC and the twist of 4-carbazole relative to the fluorene plane effectively prevent close packing between the molecules. In film state, it showed absorption and photo luminescence (PL) peaks at 409 nm and 454 nm, respectively. The carbazole terminals were intentionally incorporated to increase hole-transpoting ability and to decrease barrier height of hole injection. Furthermore, FC can be employed as hole-transporting layer (HTL) to increase hole injection. For instance, when fabricated as multi-layer OLED [ITO/PEDOT:PSS/ HTL(25 nm)/Alq3(50 nm)/LiF(0.5 nm)/Al(100 nm)], its maximum brightness (21400 cd/m2) and current efficiency (3.20 cd/A) were superior to those using NPB as hole-transpoting layer. In addition, homogeneous FC film was readily prepared by simple wet processes (spin-coating), while NPB film must be deposited by vacuum vapor deposition. Our results indicate that the FC is a promising optoelectronic material which is readily processed by wet methods as spin-coating.

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