Transparent organic light-emitting devices with
B. J. Chen, X. W. Sun, and S. C. Tan
School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue,
Singapore 639798, Singapore
Abstract: Transparent organic light-emitting devices (TOLED) based on a
stacked transparent cathode of a LiF/Mg:Ag were investigated. The device
has a structure of indium-tin-oxide (ITO)/ N, N’-diphenyl-N, N’-(3-
hydroxyquinoline) aluminum (Alq3) (80 nm)/LiF (0.5 nm)/Mg:Ag (20
nm)/Alq3 (50 nm), where the transparent capping layer of 50 nm Alq3 acts
as refractive index matching layer to optimize optical output. The turn-on
voltage of the device is as low as 2.8 V. The device also shows high optical
transparency and low reflectivity in the visible region, approximately 40%
of light can emit from the top cathode side and 60% of the light from
bottom ITO glass. At injection current density of 20 mA/cm2, the current
efficiency, for bottom emission from ITO anode side and top emission from
metal cathode side, is 3.4 cd/A and 2.2 cd/A, respectively. The lower turn-
on voltage and higher efficiency of device are due to enhancing electron
injection by using LiF/Mg:Ag cathode.
© 2005 Optical Society of America
(TPD) (90 nm)/ tris-(8-
OCIS codes: (160.4890) Organic materials; (230.3670) Light-emitting diodes; (310.6860)
Thin films, optical properties.
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(C) 2005 OSA 7 February 2005 / Vol. 13, No. 3 / OPTICS EXPRESS 937
#6082 - $15.00 US Received 16 Decenber 2004; revised 27 January 2005; accepted 28 January 2005