The characteristics of electroplex generated from the organic light emitting diodes.
The color stability and purity from OLED is of current interest. Aggregation of dyes alters the device color after fabrication of the devices. The aggregates can be exciplex and electroplex, which is the excited complex that generated after electrically excited state under high electric field. Comparative study of emission spectra of exciplex and electroplex leads us to conclude that the new electroplex states causes the bathochromic shift of the electroluminescence spectrum from the devices with TPD/PBD layers. The photoluminescence maximum obtained from the TPD/PBD layers of the device was 420 nm, and the electroluminescence maximum obtained from the device became 480 nm. The bathochromic shift cannot be attained with photoluminescence study with highly concentrated TPD/PBD mixture. This clearly indicates that the 480 nm spectrum of the devices is not resulted from the exciplex formation with TPD and PBD. We observed the overshoot in EL spectrum from the OLEDs. The most intense overshoot was observed at 460 nm, which is due to the aggregate that are formed after the electric field has been removed from the devices.
Department of Chemical Engineering, Hongik University, Seoul 121-791, Korea.
Dong-Myung
DM
Shin