高效率白光有機發光二極體之研究

Abstract

一個高效率的元件可由高效率的磷光材料，或是摻雜p型和n型的物質而使元件的電壓大幅降低而達到高效率。基於上述本論文探討兩個高效率的元件：一是利用高效率的磷光天藍光客發光體， iridium(III)bis(4,6-di-fluorophenyl)-pyridinato-N,C2) picolinate (FIrpic)和高效率的磷光黃光客發光體， (2-2’-(4-flurophenyl)benzothiozolato-N,C2’) platinum ( acetylacetonate ) (Pt(F-bt)acac)，以具有高能階1,3-Bis(carbazol-9-yl) -benzene (mCP)為主發光體。利用黃光客發光體平面分子特性，產生堆疊使得兩分子間鉑重金屬產生作用而形成活化複體(Excimer)，使得該頻譜產生紅位移現象再搭配天藍光而得到寬頻譜的白光。該元件最大電流效率為19.68 cd/A，最大外部量子效率為10.94%，色座標為(0.399,0.453)且色偏x,y值小於0.02之白光。

另外以WO3和Cs2CO3分別摻雜於電洞傳輸層(N,N’-dipheny1 -N,N’-(2-napthy1)-4,4’-diamine，NPB)和電子傳輸層(4,7-Diphenyl-1,10- phenanthroline，BPhen)當作p型和n型。藉由在電子傳輸層和發光層中間加入藍光發光層(雙層發光層)，在配合有效的電洞阻擋層( 1,1-Bis [N,N-di(p-tolyl)amin-ophenyl]-cyclohexane TPAC)和電子阻擋層(BPhen)可以改善元件隨不同電流密度下色偏的情況(相對於單層發光層)。可得到最大電流效率為10.13 cd/A，最大能量效率為10.48 lm/W，色座標為 (0.319,0.427)且在100~2000 nits下色偏(x,y)值小於0.02之白光。

接著將p-i-n白光元件串聯，由於尚未將其最佳化使得光學滿足建設性干涉。因此該元件的電壓為一個白光元件的兩倍但效率卻只有1.6倍。該元件最大電流效率為16.7 cd/A，最大能量效率為7.79 lm/W，色座標為 (0.266,0.402) 且色偏分別在200~4000 nits下及視角0~60度下色偏分別小於0.02和0.03之白光。

We have demonstrated high-efficiency i-i-i three-wavelength WOLEDs with a new orange phosphorescent dopant of Pt complex which produces excimer emission including green, yellow and red region of visible spectrum. A maximum EQE of 10.94%, luminance efficiency of 19.68 cd/A, NTSC ratio of 60.9% and a stable chromaticity with a near constant CIE coordinates under different drive current conditions were achieved. We also demonstrated a high-efficiency two-wavelength and also color stable p-i-n white device with double emitting layer and two blocking layer of TAPC and BPhen, that achieved a power efficiency of 9.2 lmW-1 (maximum：10.48 lmW-1), current efficiency of 9.86 cdA-1(maximum：10.13 cdA-1) at 1000 cdm-2, NTSC ratio of 60.9% and the change of CIE(x,y) coordinate from 100 to 2000 cdm-2 was less than (0.02, 0.02). Furthermore, we stacked two p-i-n WOLEDs. A color stable and high-efficiency two-unit WOLEDs achieved a power efficiency of 6.16 lmW-1 (maximum：7.79 lmW-1), current efficiency of 16.7 cdA-1(maximum：16.78 cdA-1) at 20mAcm-2, NTSC ratio of 60.9%.The change of CIE(x,y) coordinate of this stacked WOLEDs are essentially unchanged from luminance of 200 to 4000 cdm-2 and with respect to viewing angle of 0~60∘.