Temperature Dependence of Degradation in Organic Light-Emitting Diodes

Prolonged operation of an OLED degrades the luminance and alters the voltage-dependent capacitance. The loss of luminance in simple blue and green fluorescent OLEDs is linearly correlated with internal charge accumulation at the HTL/LEL interface. The shapes of the EL decay curve and the transition-voltage-rise curve are independent of temperature. Proper scaling of the time axis makes plots of EL or transition voltage vs. time at different temperatures to coincide. The resulting universal decay curves are not altered by the introduction of the fluorescent dopant, suggesting that the degradation processes are the same in the doped and undoped devices. Red fluorescent OLEDs of more complicated structure degrade in a dopant-dependent manner.