Efficient Sky-Blue Organic Light-Emitting Diodes Using a Highly Horizontally Oriented Thermally Activated Delayed Fluorescence Emitter

Organic thermally activated delayed fluorescent (TADF) materials can harvest 100% of the electrically generated excitons as a result of their small singlet–triplet energy difference. However, maximizing the external quantum efficiency (EQE) of a device also requires enhancing the light out‐coupling efficiency. This work presents a new acceptor–donor–acceptor (ADA) emitter employing an indolocarbazole donor and diphenyltriazine acceptors that show nearly‐completely horizontal orientation regardless of the host matrix, leading to a sky‐blue organic light‐emitting diode (λ$_{EL}$ = 483 nm, CIE coordinates of 0.17, 0.32) with EQE$_{MAX}$ of 22.1%, a maximum luminance of 7800 cd m$^{-2}$, and blue emission.