||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.