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Title: | 脈衝操作有機發光二極體及藍色元件壽命延長之研究 Study on organic light-emitting diodes under pulse operation and lifetime elongation of blue device |
Authors: | Bo-Yen Lin 林伯彥 |
Advisor: | 李君浩(Jiun-Haw Lee) |
Keyword: | 脈衝操作,陷阱電荷,三重態三重態消滅,激子淬熄, pulse operation,trapped charge,TTA and exciton quenching, |
Publication Year : | 2017 |
Degree: | 博士 |
Abstract: | 本論文有二部分,第一部分以tris(8-hydroxyquinolate)aluminum (Alq3) 作為發光層及電子傳輸層製作綠色有機發光元件,並以脈衝方式驅動。相較於直流驅動,發現在脈衝驅動下,元件之電流密度和亮度會下降, 透過電壓-電容量測和位移電流量測分析,得知其原因來自Alq3材料中之電子陷阱效應。而我們可以施以負偏壓在脈衝關閉的區間來提升電流密度及亮度,並可以超過在直流驅動下的電流密度及亮度。同樣藉由位移電流量測可以知道是陷阱正電荷在Alq3與陰極的介面幫助了電子的注入。在正偏壓與負偏壓之間加入一段約~2毫秒長的零偏壓,可以發現亮度與電流密度會降低至與沒施加負偏壓下的情況相同,此現象是由於陷阱電荷隨時間的消逝。
在論文的第二部分,我們使用彩豐精技股份有限公司所開發的一系列電子傳輸材料,製作藍色三重態-三重態消滅有機發光元件,並探討其衰退機制。我們發現元件衰退的主因,來自於電洞傳輸層的損壞,因為複合區較接近電洞傳輸層和發光層的介面。為改善元件操作壽命,我們使用具較深最低電子未佔據軌域之電子傳輸材料,搭配合適主體材料,並藉由膜層厚度最佳化,及發光層結構調變,得到了長壽命的藍色三重態-三重態消滅有機發光元件,其元件的操作壽命在1000 nits的初始亮度下約有56,048 小時,可以得到如此長壽命的原因為減少了電洞傳輸層的損壞,較寬的復合區,以及較少的激子淬熄。 There are two parts in this dissertation. In the first part, we demonstrated device performances of a green organic light-emitting diode (OLED) under pulse operation based on tris(8-hydroxyquinolate)aluminum (Alq3) as the emitting layer (EML) and the electron transporting layer (ETL) material. Compared to direct current (DC) driving, we found that current density and luminance were lower under pulse operation due to the trapped electrons in the Alq3 layer from the analysis of capacitance-voltage (C-V) measurement and displacement current measurement (DCM). Besides, we also demonstrated the enhancement of current density and luminance of the OLED under pulse mode driving by applying a reverse bias during the “off”-period, which can overpass the current density and luminance values under DC driving. From DCM, we can deduce that increase of current density and luminance resulting from the positive charges trapped in Alq3 layer close to the cathode interface during off-period by reverse bias, which facilitated the electron injection during the on-period. With the insertion of zero-bias period for ~2 ms between positive and negative pulse, current density and luminance decreased to the case without the negative bias due to the relaxation of the trapped charges. In the second part, we used a series of new electron transporting layer (ETL) materials, provided by Nichem Fine Technology Co. Ltd. to fabricate the blue triplet-triplet annihilation (TTA) OLEDs for investigating the physical mechanisms of operation lifetime. It was found that hole transporting layer (HTL) degraded because the recombination zone was near the HTL/ EML interface. To improve operation lifetime, we used the new ETL with deep lowest unoccupied molecular orbital (LUMO) level, optimized the layer thickness, and changed the EML configuration. Long lifetime blue TTA-OLED was demonstrated, which exhibited the half lifetime of 56,048 hours at initial luminance of 1,000 nits because of less degradation of HTL material, wider recombination zone, and less exciton quenching. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/68258 |
DOI: | 10.6342/NTU201704278 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 光電工程學研究所 |
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ntu-106-1.pdf Restricted Access | 5.32 MB | Adobe PDF |
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