A photochemical investigation into operational degradation of arylamines in organic light-emitting diodes

Abstract

In this study, we investigated the operational degradation of 4,4′-bis(N-carbazolyl)biphenyl (CBP), an arylamine commonly used as phosphorescent host or hole transport material in organic light-emitting diodes (OLEDs), which have been subject to a recent surge in demand for use in the optical display market. In view of the important roles of organic components in the stability and lifetime of OLEDs, we initiated an investigation of the operational degradation of CBP in OLEDs in an effort to elucidate the degradation mechanism. Our experimental approach to this task is by performing photochemistry on CBP in solution, thereby avoiding actual operation of CBP-based OLEDs. Prior to the experiments, we calculated the C–N homolytic bond dissociation energy in CBP, and synthesized two CBP derivatives based on molecular engineering considerations. Furthermore, we performed TiO2 photocatalytic decomposition of arylamines as a feasibility test for another operational degradation pathway. Based on both the photochemical and photocatalytic experiments, multiple operational degradation pathways of arylamines emerge.