Triarylboron compounds have attracted much attention, and found wide use as functional materials because of their electron‐accepting properties arising from the vacant p orbitals on the boron atoms. In this study, we design and synthesize new donor–acceptor triarylboron emitters that show thermally activated delayed fluorescence. These emitters display sky‐blue to green emission and high photoluminescence quantum yields of 87–100 % in host matrices. Organic light‐emitting diodes using these emitting molecules as dopants exhibit high external quantum efficiencies of 14.0–22.8 %, which originate from efficient up‐conversion from triplet to singlet states and subsequent efficient radiative decay from singlet to ground states.