By Andrey Y. Sosorev, Dmitry I. Dominskiy and Nikita O. Dubinets
Abstract: Luminophores featuring thermally activated delayed fluorescence (TADF) are the workhorses
of the third- and fourth-generation OLEDs. While these compounds have usually been used as dopants
embedded in the host, non-doped TADF OLEDs have recently shown significant progress as well and
have attained performances comparable to those of the host-dopant systems. For efficient operation
of non-doped OLEDs, the charge transport in neat films and single crystals of TADF luminophores is
important; however, this issue was nearly unexplored theoretically. In the current study, we calculated
the charge-carrier mobilities in four single crystals of TADF luminophores that have different molecular
packing motifs. Specifically, in one of them both the donor and acceptor moieties form uniform -stacks,
while in the others the donors (acceptors) show alternating lateral shifts along the stacks; the difference
in the molecular packing resulted in the difference in the transfer integrals between the molecules. The
reorganization energies differed as well by up to four times for the studied crystals. As a result, the
charge mobilities varied from 0.001 to ~0.3 cm2/(Vs), with the largest being predicted for the crystal of
the luminophore that consisted of a rigid donor and acceptor. We anticipate that the results obtained
will be useful in the design of TADF luminophores for non-doped OLEDs, OLETs, and other organic
light-emitting devices.
