Harvesting Triplet
Excitons with Exciplex Thermally Activated Delayed Fluorescence Emitters
toward High Performance Heterostructured Organic Light-Emitting Field
Effect Transistors
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Abstract
The
utilization of triplet excitons plays a key role in obtaining high
emission efficiency for organic electroluminescent devices. However,
to date, only phosphorescent materials have been implemented to harvest
the triplet excitons in the organic light-emitting field effect transistors
(OLEFETs). In this work, we report the first incorporation of exciplex
thermally activated delayed fluorescence (TADF) emitters in heterostructured
OLEFETs to harvest the triplet excitons. By developing a new kind
of exciplex TADF emitter constituted by m-MTDATA (4,4′,4″-tris(<i>N</i>-3-methylphenyl-<i>N</i>-phenylamino)triphenylamine)
as the donor and OXD-7 (1,3-bis[2-(4-<i>tert</i>-butylphenyl)-1,3,4-oxadiazo-5-yl]benzene)
as the acceptor, an exciton utilization efficiency of 74.3% for the
devices was achieved. It is found that the injection barrier between
hole transport layer and emission layer as well as the ratio between
donor and acceptor would influence the external quantum efficiency
(EQE) significantly. Devices with a maximum EQE of 3.76% which is
far exceeding the reported results for devices with conventional fluorescent
emitters were successfully demonstrated. Moreover, the EQE at high
brightness even outperformed the result for organic light-emitting
diode based on the same emitter. Our results demonstrate that the
exciplex TADF emitters can be promising candidates to develop OLEFETs
with high performance