Abstract
ABSTRACTPure organic-based thermally activated delayed fluorescent (TADF) emitters have been studied for the last five years because of their potential as high-efficiency emitters comparable to phosphorescent emitters. Although the initial external quantum efficiency (EQE) of the TADF emitters was much lower than that of phosphorescent emitters, the current EQE of the TADF organic light-emitting diodes (OLEDs) is quite similar to that of phosphorescent OLEDs. In particular, the EQE of the green TADF OLEDs is already over 30% with the help of the new molecular design fully harvesting triplet excitons of the TADF emitters for light emission through the up-conversion process. In this work, the progress of the device performances of the TADF OLEDs was studied by reviewing the green TADF emitters that had been developed in the last five years.
Highlights
Activated delayed fluorescent (TADF) emitters are becoming very popular because of their high external quantum efficiency (EQE) due to their efficient radiative transition process assisted by the up-conversion process of triplet excitons
The green thermally activated delayed fluorescent (TADF) emitters were more efficient than the red TADF emitters, and the green TADF OLEDs already reached the EQE level of the green phosphorescent organic light-emitting diodes (PHOLEDs) by engineering TADF emitters and host materials for the TADF emitters
The main reason for this is the design versatility of the green TADF emitters, which permits the donor and acceptor moieties for the green TADF emitter to be diversely selected based on various combinations, such as strong donor–weak acceptor, weak donor–strong acceptor, and moderate donor–moderate acceptor
Summary
Activated delayed fluorescent (TADF) emitters are becoming very popular because of their high external quantum efficiency (EQE) due to their efficient radiative transition process assisted by the up-conversion process of triplet excitons. The non-radiative triplet excitons, can be converted to singlet excitons in the TADF emitters through the reverse intersystem crossing process induced by the weak spin-orbit coupling and the small singlet–triplet energy gap ( EST) in specially designed donor–acceptor structures [1]. There has been much progress in the EQE of the red, green, and blue TADF devices for the last five years, and the most significant advances were made in the green TADF devices because of the relatively easy molecular design of the green TADF emitters. The chemical structures and device performances of the green TADF emitters were covered based on the literature data reported for the last couple of years to provide a guideline for the development of high-efficiency TADF organic light-emitting diodes (OLEDs) as the device performances of the green TADF emitters are quite similar to those of the green phosphorescent emitters. The relationship between the chemical structures and the various material parameters is discussed, and their effect on the device performances is described
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