2 research outputs found
Efficient Thermally Activated Delayed Fluorescence Conjugated Polymeric Emitters with Tunable Nature of Excited States Regulated via Carbazole Derivatives for Solution-Processed OLEDs
For
main-chain-type thermally activated delayed fluorescence (TADF)
polymeric emitters, conjugated or nonconjugated monomers are generally
copolymerized as the spacers to suppress the inter- and intramolecular
exciton concentration quenching. In this work, carbazole derivatives
are introduced into the main chains of the conjugated polymers based
on the TADF unit, 2-(10<i>H</i>-phenothiazin-10-yl)dibenzothiophene-<i>S</i>,<i>S</i>-dioxide (DBTO2-PTZ). It is found that
the content of carbazole derivatives units could not only effectively
suppress exciton quenching and nonradiative transition but also manipulate
the distribution of molecular orbits and Δ<i>E</i><sub>ST</sub> values and even regulate the nature of excited states.
Therefore, the upconversion of triplet exciton from triplet to singlet
excited state could be regulated by introducing the different contents
of carbazole derivatives. Among three synthesized polymers, COP-10
displays a relatively higher <i>k</i><sub>RISC</sub> and
PLQY in the film state. The optimized OLED device without any TADF
assistant dopant could reach to an EQE<sub>max</sub> of 15.7% with
a lower turn-on voltage of 3.2 V
Thermally Activated Delayed Fluorescence Pendant Copolymers with Electron- and Hole-Transporting Spacers
To
study the effect of hole- and electron-transporting spacers in copolymers
on the thermally activated delayed fluorescence (TADF) properties
and device efficiency of copolymers, two series of copolymers PCzPT-<i>x</i> and POPT-<i>x</i> have been designed and synthesized
successfully. In these copolymers, 2-(10<i>H</i>-phenothiazin-10-yl)dibenzothiophene-<i>S</i>,<i>S</i>-dioxide units give green-yellow TADF,
while hole-transporting 9-(4-vinylphenyl)-9<i>H</i>-carbazole
units or electron-transporting diphenyl(4-vinylphenyl)phosphine oxide
act as spacers or hosts. Their thermal, electrochemical, photophysical,
and electroluminescent properties and theoretical calculations are
systematically investigated to illustrate the relationships between
molecular structures and photophysical properties. By optimizing the
upconversion and radiative decay rate and managing the energy transfer,
a green-yellow device based on POPT-25 achieves a maximum external
quantum efficiency of 5.2%, a current efficiency of 16.8 cd/A, and
a power efficiency of 7.8 lm/W with CIE coordinates of (0.36, 0.50).
Moreover, an external quantum efficiency of 3.5% at the practical
luminescence of 100 cd/m<sup>2</sup> is obtained