Study on the degradation of sealed organic light-emitting diodes under constant current

Degradation characteristics of sealed OLED devices under four different constant currents were investigated by using OLEDs aging tester. We found that the higher the applied current density was, the faster luminance decayed. There was a relationship between luminance and lifetime when the current density was within 200 mA/cm². In addition, spectrum characterization indicated that the peak wavelength didn´t shift during the aging process, which implied that the carriers recombination occurred near the NPB/Alq₃ interface all along even when OLEDs luminance dropped down to half of the initial value, indicating that the degradation wouldn´t lead to the deviation of the carriers recombination region. Through the metallurgical microscopy observation, the number of bubbles and dark spots were noticed to increase continuously and the non-emissive area kept growing around the bubbles. It showed that bubbles would badly accelerate the formation of dark spots. By investigating luminance degradation under constant current, we draw a conclusion that OLEDs luminance degradation is not entirely coulombic. After introducing an acceleration coefficient, the formular could be applicable until the current went beyond some degree.