Green

red

blue and white organic light emitting diodes (OLED) were investigated. Remarkable improvement in stability has been demonstrated in doped green and red devices. For OLED with the structure ITO/CuPc/NPB/Alq:dopant/MgAg

copper phthalocyanine (CuPc) was used as a buffer layer

N

N’-bis-(1-naphthyl)-N

N’-diphenyl-1

1’-biphenyl-4

4’-diamine(NPB) as the hole transporting layer

tris(8-quinolinolato) aluminum complex (Alq) as ETL

indium tin oxide (ITO) and MgAg as the anode and cathode

respectively

coumarin545(C545) and quinacridone (QA) were used as the dopants for green device

while DCJTB was for the red device. For green OLED

the devices with two kinds of dopant were compared. It is shown that C545 doped device gives more higher luminance

however

its half life is shorter than that of QA doped cell. The QA doped green OLED achieved the long life of 14000h at initial luminance of 100cd/m

2

. The red OLED doped with red dye DCJTB showed high stability

the half decay time reached 7500h at the initial luminance 50cd/m

2

and the change of driving voltage was 0.6mV/hour in the degradation process. Two kinds of blue OLEDs with the structure ITO/CuPc/NPB/TPBi/Alq/MgAg and ITO/CuPc/NPB/DPVBi:perylene/Alq/MgAg were studied. The former was a device with blocking layer

here TPBi acts as a hole blocking layer due to the high barrier in the interface between it and NPB

the latter was conventional one. Luminance degradations of the two devices were compared.It showed that the blue cell with blocking layer had much shorter life time than that of the conventional cell.The latter showed the half decay time of 450h at the initial luminance 50cd/m

2

. Based on the above blue OLEDs

two white OLEDs were constructed. The structures were ITO/CuPc/NPB/TPBi:Rublene/Alq/MgAg and ITO/CuPc/NPB/DPVBi:perylene/Alq:DCJTB/MgAg.The same results about the luminance degradation have been obtained. The device without blocking layer had the half decay time of 300h at the initial luminance 50cd/m

2

. The white OLED with blocking layer had a short durability. It is concluded that the blocking layer is not favorable to the stability of the device

it may be attributed to the high barrier between the hole transporting and blocking layers.