We have fabricated a high brightness and color purity white light organic light emitting diode based on a multi-emission-layer. There were several methods to achieve white light OLEDs, including multi-emission- layer device, single emission layer device, and so on. We use RGB triple -emission-layer device to obtain white light, because its EL spectrum is broader than that of the dual-emission-layer device. Frequent problems that showed be faced in a multi-layer structure are the complicate device structure and the color various with different operation voltage. Our work includes five parts. First, we optimized the red light device by controlling the concentration of DCJTB with the configuration of ITO/NPB/Alq3: DCJTB/Alq3/LiF/Al. Second, we optimized the blue light device by controlling the concentration of TC-1753 based on a device structure of ITO/ NPB/ TC-1558: TC-1753/ Alq3/ LiF/ Al. Third, we fabricated green light device by using TPB3 as an emission layer with the configuration of ITO/NPB/TPB3/Alq3/LiF/Al. Then we optimized the dual-emission-layer white light OLED by adjusting the thickness of blue and red emission layers. Finally, we added a green emission layer into the dual emission layer device with the device structure of ITO(1300Å)/NPB(500Å)/ TPB3(500-2xÅ)/ TC-1558(xÅ): TC-1753(2%)/ Alq3(xÅ): DCJTB(2%)/ Alq3(350Å)/ LiF(8Å)/Al(2000Å). By controlling the thickness of each emission layer, a stable white OLED was achieved. The thickness of emission layer were TPB3(200Å)/ TC-1558(150Å):TC-1753(2%)/ Alq3(150Å):DCJTB(2%). The maximum luminance reached 48200 cd/m2 at 13.5V, the maximum current efficiency and power efficiency were 4.06 cd/A at 13V and 1.9 lm/W at 20mA/cm2, respectively. The CIE coordinate varied from (0.339, 0.317) to (0.339, 0.327) with an applied voltage from 9V to 13.5V. We have overcome the problem of instable color purity which was the critical disadvantage of multi-emission-layer white light OLEDs. Our study performed a high brightness and color purity white light device.

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.

Zugl.: Braunschweig, Techn. Univ., Diss., 2006

Zugl.: Braunschweig, Techn. Univ., Diss., 2007

Bayreuth, Univ., Diss., 2010.

Zugl.: Erlangen-Nürnberg, Universiẗat, Diss., 2009.

Techn. Universiẗat, Diss., 2006--München.

Zugl.: Erlangen, Nürnberg, Univ., Diss., 2009

München, Techn. Universiẗat, Diss., 2005.

Techn. Universiẗat, Diss., 2005--Dresden.