P‐135: Recombination Zone Monitoring of the Blue Phosphorescent Organic Light‐Emitting Diodes during Lifetime Test

Abstract

We studied the recombination zone shift during lifetime measurement in phosphorescent blue organic light‐emitting devices with a sensing layer. 3,3‐Di(9H‐carbazol‐9‐yl)biphenyl was used as a host material for a blue phosphorescent dopant and a red sensing dopant. The red sensing layer was inserted at a thickness of 2 nm at three different positions of the emitting layer to follow the recombination zone change before and after life‐time measurement by monitoring the electroluminescence spectra. We found that the recombination zone is shifted to electron transport layer side according to the luminance decrease of the device via direct monitoring of the recombination zone shift. .