The study of high efficiency red OLEDs and high efficiency single emitting layer broadband white OLEDs
This research includes two parts as mentioned: (I) High efficiency red organic electroluminescent devices and (II) High efficiency white organic electroluminescent devices with broadband EL emission spectrum based on a single emitting layer.
In part (I), we fabricated the high efficiency red organic electroluminescent devices incorporating 1,3,5-Tri(1-pyrenyl)benzene(TPB3) as the host material and 4-(dicyanomethylene)-2-tert-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as the dopant. The highly efficient energy transfer arose as a result of (i) perfect overlap between the PL spectrum of TPB3 and the absorption spectrum of DCJTB and (ii) the high fluorescence quantum yield of TPB3. A device having the configuration ITO(1300 Å)/ NPB(650 Å)/ TPB3: 2% DCJTB(400 Å) / Alq3(300Å) / LiF(8Å) / Al(2000 Å) exhibited a maximum luminance at 13.5V of 70600 cd/m2, ca. four times higher than that of the device using Alq3 as the host material at the same potential. The device¡¦s current efficiency was 4.38 cd/A and its power efficiency was 2.12 lm/W at 20 mA/cm2;the maximum current and power efficiencies were 4.83 cd/A and 3.7 lm/W, respectively. The current and power efficiencies were greater than 4 cd/A and 1 lm/W, respectively, over the large range of potentials (3.5~13.5V) with good Commission Internationale de l¡¦Eclairage (CIE) coordinates of (0.63,0.37). These results indicate that searching for a suitable host material is a promising approach toward achieving high-efficiency red OLEDs.
In part (II), we fabricated high-efficiency and color-stable broadband white organic electroluminescent devices based on a single emission layer, incorporating a green light-emitting host material which has large band gap and large Stoke¡¦s shift, doped with a red and a blue dye. TPB3 was used as the host material, and the red and blue light-emitting dyes were DCJTB and di(4-fluorophenyl)aminodi(styryl)biphenyl (DSB), respectively. A device having a simple configuration ITO(1300 Å) / NPB(650 Å) /TPB3: 10% DSB:
0.6% DCJTB(400 Å)/ Alq3(300Å) / LiF(8Å)/Al(2000 Å) exhibited a broadband white emission with a maximum luminance at 14.0 V of 81000 cd/m2, maximum current efficiency of 5.9 cd/A at 10.0 V, maximum power efficiency of 3.2 lm/W at 4.0 V. The Commission Internationale de l¡¦Eclairage (CIE) coordinates of (0.34,0.38) changed slightly over the large range of potentials (4~14.5 V). The high-efficiency¡Bhigh-bright and color-stable may be attributed to the high electroluminescence character of the host and the dopants, relatively high energy transfer from host to red dopant, and effective carrier-direct-recombination on a blue dopant, and the confinement of charge recombination zone in a single layer.
Advisor:Yu-Kai Han; Ping-Tsung Huang; Chih-Chien Lee; Mei-Ying Chang; Jui-Ming Yeh; Wen-Yao Huang
School:National Sun Yat-Sen University
School Location:China - Taiwan
Source Type:Master's Thesis
Keywords:tpb3 white red oled
Date of Publication:07/22/2008