posted on 2023-11-24, 00:55authored bySung Hoon Jung, Su Hong Park, Na Yeon Kwon, Jin Young Park, Min Ji Kang, Chang Woo Koh, Min Ju Cho, Sungnam Park, Dong Hoon Choi
In
solution-processed organic light-emitting diodes (OLEDs), achieving
high color purity and efficiency is as important as that in vacuum
processes. Emitters suitable for solution processing must have excellent
solubility in organic solvents, high molecular weight, and compatibility
with the host materials. In this study, we synthesized a deep-blue
emitter that satisfies the above conditions by introducing a 1,4-bis(indolo[3,2,1-jk]carbazol-2-yl)benzene-based planar emitting core (DICz)
structure and four 3,6-di-tert-butyl-9-phenyl-9H-carbazole (tCz) peripheral units, namely,
4tCz-DICz. A comparative compound, 4Hex-DICz, incorporating
hexyl phenyl groups was synthesized. In contrast to 4Hex-DICz, 4tCz-DICz exhibited exceptional solubility in organic solvents
and superior film-forming properties attributed to the presence of tCz units. Additionally, in the film state, the effective
encapsulation of the emitting core (DICz) by the tCz units in 4tCz-DICz helps prevent undesirable
molecular aggregation. The solution-processed OLEDs employing the
CH-2D1 film, doped with 5 wt % 4tCz-DICz as the emitting
layer, exhibited a deep-blue emission at 424 nm, characterized by
a narrow bandwidth of 22 nm, and achieved a maximum external quantum
efficiency (EQE) of approximately 4.0%. In contrast, the 4Hex-DICz-based
device demonstrated an EQE of 2.91%. Consequently, we have successfully
demonstrated that the introduction of four bulky tCz units into the DICz core is a promising molecular design strategy
for the development of soluble indolocarbazole-based emitters, especially
those used in high-performance deep-blue fluorescent OLEDs.