真空蒸鍍聚合聚亞醯胺及其有機發光二極體特性研究

Abstract

本論文係利用真空蒸鍍聚合法（Vapor Deposition Polymerization，VDP）製備聚亞醯胺（Polyimide，PI）薄膜，因製程中無溶劑使用，因此可得到無雜質、無針孔、無溶劑殘留且厚度均勻之薄膜。有效的克服傳統濕式製程，溶液存在對薄膜性質所造成的影響。而在有機發光二極體方面之應用，則具有簡化及解決許多元件製程問題之優勢。 本研究中，真空蒸鍍聚合聚亞醯胺選用2,5-Bis(4-aminophenyl)-1,3,4-oxadiazole （BAO）及4,4'-(9-Fluorenylidene)dianiline （BAPF）兩種二胺（Diamine）單體分別與4,4'-(Hexafluoroisopropylidene)diphthalic anhydride （6FDA）二酸酐單體進行聚合反應。 在薄膜製備製備及特性研究上，以傅立葉轉換紅外線光譜儀（FT-IR）鑑定薄膜結構並利用原子力顯微鏡（AFM）觀察薄膜表面性質。研究中觀察BAPF與6FDA兩單體於共蒸鍍後，熱亞醯胺化前FT-IR吸收光譜發現，並無1650㎝-1聚醯胺酸之吸收峰存在，可知BAPF與6FDA兩單體之反應性在VDP製程下，較BAO與6FDA之反應性低；而在熱亞醯胺化後，由於1380㎝-1及1720㎝-1吸收峰之明顯出現，顯示薄膜已由未反應單體或聚醯胺酸結構轉變成聚亞醯胺結構。此外，利用原子力顯微鏡觀察薄膜表面結構，在VDP製程下 BAO-6FDA及BAPF-6FDA聚亞醯胺薄膜，均方根表面粗糙度各為8.81Å及4.74Å，其中BAO-6FDA聚亞醯胺薄膜如以傳統濕式製程製備，所得薄膜均方根表面粗糙度則為37.07Å。結果如預期般，顯示以相同單體不同製程，真空蒸鍍可得到較佳表面性質之薄膜。 在有機發光二極體特性研究中，發現以PI薄膜為發光層所製成之元件，單層結構即可得到波峰極寬並涵蓋整個可見光光譜之電激發光。而且成功藉由VDP製程將PI薄膜之厚度減低至150Å，大幅度的將BAO-6FDA及BAPF-6FDA元件之啟動電壓降低至4.5V與7.5V；此外，藉由亮度-電流曲線圖可知，在VDP製程下BAPF-6FDA元件之發光效率較BAO-6FDA元件發光效率佳，由UV光譜及循環伏安計所建構之能階圖顯示：BAPF-6FDA的電子及電洞注入較為平衡。因此有較佳的發光效率。 在與傳統濕式製程所得元件性質之比較之下，光電性質結果顯示，利用VDP乾式製程，有較高的驅動電壓且較大的漏電流，此可能與由VDP製成所得的PI分子量較小，極性末端較多所致。另外，VDP製程的PI元件電激發光波峰有加寬之現象，可能也與此有關，因此VDP製程製備PI發光二極體仍有許多可研究討論的空間。

The thesis is focus on preparing Polyimide(PI) thin film by vapor deposition polymerization(VDP). The process without any solvent can produced a uniform film without impurity and pin-hole. The method can well to solve the problems of traditional wet coating process with exist of solvent throughout the process. In the field of organic light emitting diodes, we can brief and solve a lot of problems in the manufacturing of device. In my study, we synthesize Polyimide thin film with using two kind of Diamine: 2,5-Bis(4-aminophenyl)-1,3,4-oxadiazole （BAO）and 4,4'-(9-Fluorenylidene)dianiline （BAPF）and reacting with 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride （6FDA）. We imply Fourier transform infrared(FTIR) and atomic force microscopy(AFM) to investigate the characteristics of the Polyimide thin film. We observed that the peak of 1650cm-1 is not exist in the FTIR spectrum before the imidization on the Polyimide film prepared by BAPF and 6FDA. Under VDP process, we conclude that the reactivity of BAO is better than BAPF in the reaction with the 6FDA. After the thermal imidizition, the peaks of 1380cm-1 and 1720cm-1 are observed in the FTIR spectrum, we assumed that the monomers or polyamic acid convert to polyimide. On the other hands, we view The morphology of the Polyimide thin film through atomic force microscopy and find out that the root mean square of the roughness of the BAO-6FDA and BAPF-6FDA is 8.81Å and 4.74Å respectively. In the wet coating process , we gain the root mean square of the roughness of the BAO-6FDA thin film is about 37.07Å. Finally, we conclude that VDP process is better way to produce Polyimide film than the wet coating process. In the research of the organic light emitting diode, the polyimde thin film can use to be a emitting layer. A broaden peak covered the full range of visible light (400nm to 700nm) exists in the spectrum of electroluminescent light in the single layer structure . Besides, we succeeded to decrease the thickness of the Polyimide thin film until 150 Å, and lowered the threshold voltage of BAO-6FDA and BAPF-6FDA devices about 4.5V and 7.5V respectively. From the B-V Curve diagram, the efficiency of emitting light of BAPF-6FDA device is better than BAO-6FDA device, this phenomena is tally with the energy level diagram of CV. In contrast to wet process device, the Polyimde thin film prepared by VDP process has more broaden peak around the range of visible light. This can be assumed that the color of the emitting light is more nearly white.