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.