三重態-三重態消滅藍色有機發光二極體之研究

Abstract

本篇論文研究方向有二：其一為利用三重態三重態消滅上轉換機制來製作低驅動電壓藍色有機發光二極體，其二為加入輔助主體材料以延長之三重態三重態消滅藍色螢光元件之壽命。 我們利用搭配具有推電子以及拉電子能力的有機材料來形成激發複合體，再藉由能量轉移方式到藍色螢光材料進行三重態三重態消滅上轉換來放出藍光。觀察穩態亮度-電壓特性，利用三重態三重態消滅上轉換機制產生的藍光與一般傳統以直接復合方式相較起來在驅動電壓上降低了0.4伏特。另外我們以電激發光驅動元件觀測低電壓下激子暫態行為，發現當電訊號關掉以後，激子暫態放光中沒有瞬時螢光而全部是經由能量轉移形成的延遲螢光，表示此放光都是來自於三重態的貢獻，證明其機制為三重態三重態消滅上轉換藍光。 我們以加入輔助主體材料來達成89.3%延長壽命之藍色三重態-三重態消滅有機發光體。我們利用量測激子擴散長度、單載子電洞元件、單載子電子元件、探測發光區以及將元件以定電流方式持續操作一段時間後去觀察暫態電激放光，及穩態光激發光頻譜強度的變化，來了解在元件中加入輔助主體材料後扮演的角色。

There are two topics in the thesis. The first one is a blue organic light-emitting diode (OLED) with low driving voltage based on triplet triplet annihilation upconversion (TTAUC) mechanism. And the second is the operation lifetime elongation of triplet triplet annihilation (TTA) blue organic light-emitting diode by introducing assistant host material into the emitting layer (EML). We use donor and acceptor organic materials to generate exciplex which transfers triplets to the blue TTA material to realize light upconversion, called TTAUC. 0.4 V reduction in turn-on voltage was observed in blue TTAUC-OLED, compared to the conventional TTA-OLED with direct recombination in the EML. Besides, transient electroluminescence was used to study exciton dynamics. Only slow decay, coming from the energy transfer of triplets from exciplex emission, was observed during turn-off transient which proved the TTAUC emission mechanism. 89.3 % increase in operation lifetime was achieved in a blue TTA-OLED by introducing 10% assistant host (AH) material in the emitting layer. By observing the exciton diffusion length, hole-only device, electron-only device characteristics, and TrEL and photoluminescence spectra before and after device aging at constant current, we characterized the function of AH in this OLED.