红绿掺杂有机电致发光器件发光性能的研究

Luminescent properties of red and green organic light-emitting diodes by doping in the emitting layer

制备了结构为ITO/MoO3(xnm)/NPB(40nm)/CBP:14%GIr1(12.5nm)/CBP:6%R-4b(5nm)/CBP:14%GIr1(12.5nm)/BCP(10nm)/Alq3(40nm)/LiF(1nm)/Al(100nm)的红绿磷光器件,GIr1和R-4B分别为新型绿色和红色磷光染料,采用绿-红-绿掺杂顺序,结合BCP对空穴的有效限制作用,研究了不同MoO3厚度器件的发光机理。结果表明,在MoO3为40nm时,器件发光性能较好,在电压为5V、亮度为100cd·m-2时,得到最大的电流效率为16.91cd·A-1。为提高器件光效,增加TCTA电子阻挡层,获得了最高电流效率20.01cd·A-1。原因主要是,TCTA的HOMO能级介于NPB和CBP之间,促进空穴注入;TCTA较高的三线态能量对发光层激子的限制。

We have investigated the electro-optical performance of green and red phosphorescent light-emitting diodes （LEDs） with different thicknesses of MoO3, using BCP as the hole-blocking and exiton limiting layer. The device structure is. ITO/MoO3 （x nm）/NPB（40 nm）/CBP： 14%Girl（12.5 rm0/ CBP：6%R-4b（5 nm）/CBP..14% GIrl （12. 5 nm） /BCP（10 nm）/Alq3 （40 nm）/LiF（1 nm）/Al（100 nm） ,where x is 10 nm,20 nm,30 nm,40 nm and 50 nm,separately,GIrl and R-4B are green and red phosphorescent dyes respectively. By adiusting the thickness of MoO3 ,we find that the device performance depends on the thickness of MoO3 layer, and we achieve the optimal device. The results show that the device achieves the maximum luminance of 18 000 cd · m^-2 at 12 V, the highest current efficiency at the thickness of 40 nm at voltage of 5 V,lu;ninance is 100 cd · m^-2 ,and the maximum current efficiency is 16.91 cd · A^-1. To improve the efficiency of the device,we add the TCTA blocking layer and compare two types of devices,so we can obtain the highest efficiency of 20.01 cd · A^-1 ,enhanced by 19%. By analyzing the reason,we conclude that the HOMO levels of NPB,TCTA ,CBP are 5.5 eV,5.7 eV, 5.9 eV, respectively, thus promoting the hole inj ection; the triplet energy levels of TCTA, CBP are 2.85 eV,2.65 eV. The higher triplet energy difference prevents the exciton leakage from the light emitting layer.