Origin of exciplex degradation in organic light emitting diodes: Thermal stress effects over glass transition temperature of emission layer

Abstract

Exploiting exciplexes in organic light-emitting diodes (OLEDs) to enhance electroluminescence lifetime and quantum efficiency is of considerable interest to researchers. The presence of exciplexes has been demonstrated in a host material interface in a multiple stacked OLED; therefore, understanding the degradation mechanism of exciplexes and host materials is essential to develop highly reliable and uniform OLEDs. Herein, we report thermal stress-driven exciplex degradation in a blue OLED, which comprises 4,4 ' -bis(N-carbazolyl)-,1 ' -biphenyl (CBP) as a host material without dopants. The device structure dependent-electroluminescence clearly confirms the formation of exciplexes surrounding the CBP interfaces at 398 and 450nm, respectively. During the thermal stress over the glass transition temperature (T-g) of the CBP, the spectral intensity of the exciplex decreased significantly, and the ideality factor and characteristic trap energy increased abruptly when the thermal stress temperature was higher than the T-g of CBP, signaling the origin of thermal degradation effects on the exciplex and host material in our OLED.