Diindolocarbazole as a Core Structure for Narrow-Emitting and Highly Efficient Blue Organic Light-Emitting Diodes

In this study, a molecular design approach inducing high efficiency and narrow emission in blue organic light-emitting diodes (OLEDs) using indolocarbazole and diindolocarbazole backbone structures are proposed. The indolocarbazole and diindolocarbazole backbone structures are used as a core structure and the indole is protected with spiro configured fluorene for rigidity and suppressed intermolecular interaction. The indolocarbazole and diindolocarbazole derived compounds show multiple resonance-thermally activated delayed fluorescence emission even without any electron deficient unit within the molecular structure and narrow emission spectrum with a full width at half maximum (FWHM) of less than 20 nm. As a result, the blue OLEDs fabricated using the unique diindolocarbazole emitter delivered high external quantum efficiency of 28.2% and a sharp emission spectrum with a FWHM of 20 nm.