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.