The Electroluminescence Mechanism of Solution-Processed TADF Emitter 4CzIPN Doped OLEDs Investigated by Transient Measurements

Abstract

High efficiency, solution-processed, organic light emitting devices (OLEDs), using a thermallyactivated delayed fluorescent (TADF) emitter, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), are fabricated, and the transient electroluminescence (EL) decay of the device with a structure of [ITO/PEDOT: PSS/4CzIPN 5 wt % doped 4,40-N,N0-dicarbazolylbiphenyl(CBP)/bis-4,6-(3,5-di-4-pyridylphenyl)-2-methylpyrimidine (B4PyMPM)/lithium fluoride (LiF)/Al], is systematically studied. The results shed light on the dominant operating mechanism in TADF-based OLEDs. Electroluminescence in the host-guest system is mainly produced from the 4CzIPN emitter, rather than the exciplex host materials.

Persistent Dimer Emission in Thermally Activated Delayed Fluorescence Materials

“…The phenomena are related to the emissive layer only and are consistent with the emission red shifts reported in solution-processed and evaporated films by others. 9,10,12−16 Device data shown in Figure 6c,d demonstrate that the monomer and dimer concentrations within the emissive layer play a dominant role in all aspects of the device performance, both electrical and optical. The current–voltage ( J – V ) and EQE curves for the full device series are shown in Figure S18.…”

Perspective on carbazole-based organic compounds as emitters and hosts in TADF applications

“…1. 98 Wang et al 99 reported 4CzIPN ( Fig. 1) and utilized this material to provide evidence that the mechanism of electroluminescence of devices based on 4CzIPN is based on the recombination of injected carriers in the (near) absence of energy transfer processes.…”

Thermally Activated Delayed Fluorescence: Beyond the Single Molecule

“…They observed a significant redshift in the emission with increasing concentration (Figures 2A-E) and a decrease in the TADF lifetime. These red shifts, both in photoluminescence and electroluminescence, have been observed by a range of researchers (Nakanotani et al, 2013;Kim and Lee, 2014;Komatsu et al, 2015;Wang et al, 2016;Zhu et al, 2017;Li et al, 2018;Niwa et al, 2018). Kim et al (2017) attributed these red shifts and the consequential change in TADF behavior to the changing dipole moment of the surrounding matrix as the host molecules are subsequently replaced with more 4CzIPN molecules (Figure 2A).…”