Enhancement of circularly polarized electroluminescence via reflection reversal under a magnetic field

Abstract

Electroluminescent devices such as circularly polarised organic light-emitting diodes (CP-OLEDs) fabricated by conventional methods do not exhibit adequate circularly polarised electroluminescence (CPEL) with high circular polarisation. Therefore, new approaches for CPEL and CP-OLED systems are needed. We developed an external-magnetic-field-driven CP-OLED device that emits red CPEL by integrating an achiral optically inactive phosphorescent platinum(II) porphyrin luminophore (PtOEP) in the emission layer (EML). This magnetic CP-OLED system can simultaneously emit circularly polarised light with opposite rotations from the EML in the N-up and S-up directions of the applied magnetic field. By utilising this mechanism that allows simultaneous emission upon the application of a magnetic field and the reflection-reversal property of circularly polarized light, we may suppress the decrease in both the luminosity and circular polarisation of CPEL. The direction of rotation of CPEL was successfully reversed by switching the Faraday geometry of the applied magnetic field. This approach can promote the development of novel CP-OLED devices.