Thermal behavior and indirect life test of large-area OLED lighting panels

Abstract

In this work, we studied the thermal behavior and addressed the challenges of life testing of large area OLED devices. In particular, we developed an indirect method to accurately calculate the life time of large-area OLED lighting panels without physically life-testing the panels. Using small area OLEDs with structures identical with the tested panels, we performed the life tests at desired driving current densities at different temperatures and extracted the relationship between junction temperature and the lifetime for the particular device. By measuring the panel junction temperature during operation under the same current density and using the life time measured on small area test devices, we determine the lifetime of the panels based on the thermal dependence. We test this methodology by predicting the life time of white PHOLED panels and then physically testing the panels. The typical result for the lifetime to 80% of the initial luminance (LT80) of the panel at a constant dc current density of 10 mA/cm 2 (3800 cd/m 2 ), was predicted to be 526 hours in good agreement with the actual life-test at 10 mA/cm 2 of 512 hrs. This good agreement, confirmed in different experiments, validates this novel technique as a practical life time predictor of large-area OLED lighting panels in a time saving manner.