LI Feng-hong, TIAN Wen-jing, WU Ying, WU Fang, SHEN Jia-cong. Effect of Cathode on Performance of Blue Organic Electroluminescence Device[J]. Chinese Journal of Luminescence, 2000,21(3): 265-268
LI Feng-hong, TIAN Wen-jing, WU Ying, WU Fang, SHEN Jia-cong. Effect of Cathode on Performance of Blue Organic Electroluminescence Device[J]. Chinese Journal of Luminescence, 2000,21(3): 265-268DOI:
Since the discovery of efficient organic light-emitting devices (OLEDs)
there has been considerable interest in developing OLEDs with high brightness
high efficiency
and long lifetime for display applications. This has resulted in substantial research activity to increase the carrier mobility
color gamut
and electroluminescence efficiency of organic materials
as well as to improve electron and hole injection by the contacts. The brightness and efficiency of OLEDs depend on the number density of electrons and holes in the emission layer
so that effective charge injection into the organic materials is critical for optimum device performance. For the hole injecting contact
indium tin oxide (ITO) is often used because of its transparency and high work function (5.1eV). On the other hand
an efficient electron-injecting contact is usually a low work function material such as magnesium
calcium
or lithium. These materials are typically alloyed with metal such as aluminum or silver to form contact that is both more stable and more resistant to corrosion upon exposure to air. At the same time inserting an insulating layer between cathode and organic material is effective means to improve current injection and EL. In this paper
some multilayers OLEDs were fabricated using Al
LiF/Al and Mg:Ag as cathode respectively while ITO-coated glass as anode
1
2
3
4
5-pentaphenyl-1
3-cyclopentadiene(PPCP) as emitter
N
N′-diphenyl-N
N′-bis(3-methyl-phenyl)-(1
1′-biphenyl)-4
4′-diamine(TPD) as hole-transport layer
tris(8-hydroxyquinoline)aluminum(Alq)
2-(4-biphenylyl)-5-(4-tertbutyl-phenyl)-1
3
3-oxadiazole(PBD) or 2
5-bis(5-tert-butyl-2-benzoxazolyl)thiophene(BBOT) as electron-transport layer
respectively. And effect of cathode on performance of blue OLEDs was studied. All organic layers were prepared by a high vacuum multisource type organic molecular deposition system. From result
it is found that the performance of device with LiF/Al as cathode excels that of the device with Al or Mg:Ag as cathode. Devices with LiF/Al show better
I-V
characteristics and higher EL efficiency. The presence of LiF at the metal-organic material interface cause band bending of organic material