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. 2018 May 9;8(31):17025-17033.
doi: 10.1039/c8ra01761a.

δ-Carboline-based bipolar host materials for deep blue thermally activated delayed fluorescence OLEDs with high efficiency and low roll-off characteristic

Ji Su Moon  1 , Dae Hyun Ahn  1 , Si Woo Kim  1 , Seung Yeon Lee  1 , Ju Young Lee  1 , Jang Hyuk Kwon  1
Affiliations

δ-Carboline-based bipolar host materials for deep blue thermally activated delayed fluorescence OLEDs with high efficiency and low roll-off characteristic

Ji Su Moon et al. RSC Adv. .

Abstract

Two bipolar host materials, 8-(9H-carbazol-9-yl)-5-(pyridin-2-yl)-5H-pyrido[3,2-b]indole (CzCbPy) and 5-(6-(9H-carbazol-9-yl)pyridin-2-yl)-8-(9H-carbazol-9-yl)-5H-pyrido[3,2-b]indole (2CzCbPy), were synthesized for deep blue thermally activated delayed fluorescence organic light emitting diodes (TADF OLEDs). Both CzCbPy and 2CzCbPy hosts possess bipolar characteristic with high polarity, which results in high delayed photoluminescence quantum yields by reducing the energy gap between singlet and triplet states of TADF materials. In addition, these hosts have high enough triplet energies of 3.05 eV to transfer exciton energy to a deep blue TADF emitter. A deep blue TADF OLED fabricated with a CzCbPy host exhibited high external quantum efficiency of 22.9% and low efficiency roll-off (19.2% at 1000 cd m-2).

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Conflict of interest statement

There are no conflicts to declare.

Figures

Scheme 1
Scheme 1. Synthesis of CzCbPy and 2CzCbPy.
Fig. 1
Fig. 1. Molecular structures and HOMO/LUMO distributions of CzCbPy and 2CzCbPy in geometry optimization state by DFT simulation with B3LYP/6-31G*.
Fig. 2
Fig. 2. UV-vis absorption (black dash line), PL spectrum at 300 K (black solid line) and 77 K (red solid line) in toluene 10−5 M solution. (a) CzCbPy, (b) 2CzCbPy.
Fig. 3
Fig. 3. Transient PL decay curves of mCP, CzCbPy, and 2CzCbPy films doped with 20 wt% DMAC-DPS.
Fig. 4
Fig. 4. (a) Diagram of the evaluated device structure and energy level of the device. (b) The molecular structures of material for each layer.
Fig. 5
Fig. 5. (a) J–V–L characteristics (b) CE-L curves, (c) EQE-L curves, and (d) EL spectra of blue TADF-OLEDs using mCP, CzCbPy and 2CzCbPy with DMAC-DPS.
Fig. 6
Fig. 6. J–V characteristics of (a) HOD and (b) EOD of mCP, CzCbPy, and 2CzCbPy.
Fig. 7
Fig. 7. Molecular packing simulation results of (a) CzCbPy and (b) 2CzCbPy.
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