The color stability and purity from OLED is of current interest. Aggregation of dyes alters the device color after fabrication of the devices. Exciplex and electroplex formations have been proposed to explain the aggregate color change. We investigate the possibility of exciplex formation and propose the new electroplex state that can cause the bathochromic shift of the electroluminescence spectrum from the devices with TPD/PBD layers. The photoluminescence maximum of the device was 420nm, and the electroluminescence maximum of the device to became 480nm. The bathochromic shift cannot be attained with photoluminescence study with highly concentrated TPD/PBD mixture. This clearly indicates that the 480nm 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 460nm, which may be due to the aggregates that are formed after the electric field has been removed from the devices.

• Sung-Taek Lim
• Byoung-Chung Sohn
• Dong-Myung Shin