高效率磷光敏化固態紅外光電化學元件

Abstract

有機發光二極體(Organic light-emitting devices, OLEDs)因為擁有低驅動電壓需求、可撓性、元件重量輕等優點，於紅外光領域中逐漸受人注目，其優勢在光通訊、偵測、生醫等應用方面擁被視為有相當的潛力發展。但是傳統OLEDs複雜的多層結構以及低功函數金屬電極需求卻成為其發展的不利因素。 因此紅外光有機發光電化學元件(Light-emitting electrochemical cells, LECs)提供一種新型態的改良概念，除含有傳統OLEDs的優點之外，LECs更擁有單層結構的特色以及可使用在空氣穩定的金屬作為電極的優點。但目前不論是以共軛高分子或者離子性過渡金屬錯合物作為發光材料的紅外光有機發光電化學元件，都面對效率普遍低落的狀況。 本論文發表三種磷光敏化主客體摻雜固態有機發光電化學元件，並探討其元件特性。 吾人採用溶液製程製作單層結構元件，分別採用銦錫氧化物與銀為陽極及陰極，在發光層內則應用主客體摻雜系統，以磷光材料離子性過渡金屬錯合物[Ir(ppy)2(dasb)]+(PF6)─為主體材料，添加有機鹽類BMIM+(PF6) ─，並分別搭配DTTCI、IR-780、IR-895三種螢光雷射染料以低濃度作為客體材料提供主要發光。 並藉由實驗分別對三種摻雜客體製作之元件，進行主客體摻雜濃度的探討、以及操作電壓對元件特性的探究，其中包含對元件的發光頻譜光色、電流密度、元件亮度以及效率的影響。同時證實主客體之間能障造成的載子捕捉機制主導部分發光機制，以及最後考量以上結果，得到元件各條件的最佳參數，此時DTTCI、IR-780、IR-895三種雷射染料作為客體材料的有機發光電化學元件，得到波長810 nm、820 nm與990 nm紅外光，並且在紅外光色純淨的要求之下，分別達到1.24 %（7.84 mW/W）、0.54 %（3.33 mW/W）、0.21 %（1.18 mW/W）的外部量子效率與能源效率。最終本論文製作之元件最高外部量子效率達紅外光有機發光電化學元件自發展以來文獻紀錄十六餘倍的效率提升，證實藉由磷光敏化主客體摻雜系統能有效提升紅外光有機發光電化學元件效率。

Organic light-emitting devices (OLEDs) have attracted attention in the infrared technology due to several advantages such as low power consumption, flexible substrates, and light weight. Those superiorities make it be regarded as having potential applications in telecommunications, displays and bio-imaging. Yet traditional OLEDs typically require sophisticated multilayer structures and low-work-function cathodes to optimize device efficiencies which tune into the encumbrances of development. Hence, solid-state NIR light-emitting electrochemical cells (LECs) provide a concept of improving. LECs not only possess the advantages of OLEDs, but generally require only a single emissive layer, which can be easily processed from solutions, and can conveniently use air-stable electrodes. However, nowaday infrared LECs devices based on conjugate polymers or transition metal complexes exhibit low device efficiencies. In this work, three different phosphorescent sensitized fluorescent solid-state near-infrared light-emitting electrochemical cells have been fabricated and discussed. We fabricated those single-layered infrared LECs with the use of solution process. Those LECs take Indium tin oxide substrates as anode and Ag as cathode. The emission layer deposited between electrodes utilizing host-guest doping system containing orange emitting phosphorescent ionic transition metal complex[Ir(ppy)2(dasb)]+(PF6)─ as the host, organic salt BMIM+(PF6)─, and three different ionic fluorescent infrared laser dye DTTCI, IR-780 and IR-895 as the guest. Through our experimental study, bias-voltage and guest-concentration dependence on characteristics, such as electroluminescence (EL), spectrum current density and device efficiency are discussed. Furthermore, it confirm that direct carrier trapping due to the large energy offsets between the energy levels of the host and the guest molecules plays an important role in emitting mechanism. Based on the analysis above, we received the optimal parameter for each device. Therefore the EL spectra of three laser dye DTTCI, IR-780 and IR-895 reveal center at c.a. 810 nm, 820 nm and 990 nm, respectively. In addition, the device efficiencies achieve peak EQE (power efficiency) up to 1.24 % (7.84 mW/W), 0.54 % (3.33 mW/W) and 0.21 % (1.18 mW/W), respectively. Those device efficiencies by a great margin achieved the highest for NIR LECs have been reported so far over sixteen times and thus confirm that phosphorescent sensitized fluorescence is useful for achieving efficient NIR LECs.