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Suppressing exciton deconfinement and dissociation for efficient thermally activated delayed fluorescence OLEDs
- Source :
- Journal of Applied Physics, Journal of Applied Physics, 130(15):155501. American Institute of Physics
- Publication Year :
- 2021
-
Abstract
- The efficiency of organic light-emitting diodes that utilize the principle of thermally activated delayed fluorescence (TADF) depends sensitively on the host material in which the TADF emitter molecules (guests) are embedded. Potential loss processes are "deconfinement,"the transfer of excitons from the guest to the host, and "dissociation,"the formation of intermolecular charge-transfer states. We investigate how both processes can be suppressed by studying the photoluminescence efficiency, emission spectrum, and time-resolved emission intensity of eight thin-film systems in which 5 mol. % of the sky-blue TADF emitter 4-carbazolyl-methylphthalimide (abbreviated here as CzPIMe) is embedded in various host materials. Deconfinement is found to be entirely suppressed if the triplet energy of the host is 0.25 eV or more above that of the guest. For systems allowing for deconfinement, the dependence on the energy difference is consistent with a recent theoretical analysis [C. Hauenstein et al., J. Appl. Phys. 128, 075501 (2020)]. Dissociation, due to hole transfer to a host molecule, is found to be suppressed if the host's highest occupied molecular orbital energy is not more than about 0.2 eV higher than that of the guest. Otherwise, we observe an efficiency loss, a spectral redshift, and the disappearance of distinct prompt and delayed emission regimes. A comprehensive rate-equation model is developed from which we study the sensitivity of these observations to the energy level structure, the intermolecular interaction rates, and the photophysical rates that follow from a fit to the experimental data for the CzPIMe:TCTA [tris (4 - carbazoyl - 9 - ylphenyl) amine] system.
- Subjects :
- Materials science
Photoluminescence
Exciton
Intermolecular force
General Physics and Astronomy
02 engineering and technology
010402 general chemistry
021001 nanoscience & nanotechnology
01 natural sciences
Deconfinement
Dissociation (chemistry)
0104 chemical sciences
13. Climate action
Chemical physics
Molecule
Emission spectrum
0210 nano-technology
HOMO/LUMO
Subjects
Details
- ISSN :
- 00218979
- Database :
- OpenAIRE
- Journal :
- Journal of Applied Physics
- Accession number :
- edsair.doi.dedup.....ff9349c7f6f7c9cad489543d5edec330
- Full Text :
- https://doi.org/10.1063/5.0062926