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Keywords = TADF assistant dopant

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16 pages, 3035 KB  
Article
Efficient OLEDs Based on Slot-Die-Coated Multicomponent Emissive Layer
by Ewelina Witkowska, Ireneusz Glowacki, Tung-Huei Ke, Pawel Malinowski and Paul Heremans
Polymers 2022, 14(16), 3363; https://doi.org/10.3390/polym14163363 - 17 Aug 2022
Cited by 11 | Viewed by 3960
Abstract
The optimization of multicomponent emissive layer (EML) deposition by slot-die coating for organic light-emitting diodes (OLEDs) is presented. In the investigated EMLs, the yellow-green iridium complex (Ir) was doped in two types of host: a commonly used mixture of poly(N-vinylcarbazole) (PVK) [...] Read more.
The optimization of multicomponent emissive layer (EML) deposition by slot-die coating for organic light-emitting diodes (OLEDs) is presented. In the investigated EMLs, the yellow-green iridium complex (Ir) was doped in two types of host: a commonly used mixture of poly(N-vinylcarbazole) (PVK) with oxadiazole derivative (PBD) or PVK with thermally activated delayed fluorescence-assisted dopant (10-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-10H-spiro[acridine-9,9′-fluorene], SpiroAC-TRZ). In this article, OLEDs with EML prepared in air by slot-die coating, facilitating industrial manufacturing, are confronted with those with spin-coated EML in nitrogen. OLEDs based on PVK:PBD + 2 wt.% Ir-dopant exhibit comparable performance: ~13 cd A−1, regardless of the used method. The highest current efficiency (21 cd A−1) is shown by OLEDs based on spin-coated PVK with 25 wt.% SpiroAC-TRZ and 2 wt.% Ir-dopant. It is three times higher than the efficiency of OLEDs with slot-die-coated EML in air. The performance reduction, connected with the adverse oxygen effect on the energy transfer from TADF to emitter molecules, is minimized by the rapid EML annealing in a nitrogen atmosphere. This post-treatment causes more than a doubling of the OLED efficiency, from 7 cd A−1 to over 15 cd A−1. Such an approach may be easily implemented in other printing techniques and result in a yield enhancement. Full article
(This article belongs to the Collection State-of-the-Art Polymer Science and Technology in Poland)
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19 pages, 5515 KB  
Article
Effect of TADF Assistance on Performance Enhancement in Solution Processed Green Phosphorescent OLEDs
by Ewelina Witkowska, Gabriela Wiosna-Salyga, Ireneusz Glowacki, Tung-Huei Ke, Pawel Malinowski and Paul Heremans
Polymers 2021, 13(7), 1148; https://doi.org/10.3390/polym13071148 - 2 Apr 2021
Cited by 5 | Viewed by 5055
Abstract
Many methods have been proposed to increase the efficiency of organic electroluminescent materials applied as an emissive layer in organic light emitting diodes (OLEDs). Herein, we demonstrate enhancement of electroluminescence efficiency and operational stability solution processed OLEDs by employing thermally activated delayed fluorescence [...] Read more.
Many methods have been proposed to increase the efficiency of organic electroluminescent materials applied as an emissive layer in organic light emitting diodes (OLEDs). Herein, we demonstrate enhancement of electroluminescence efficiency and operational stability solution processed OLEDs by employing thermally activated delayed fluorescence (TADF) molecules as assistant dopants in host-guest systems. The TADF assistant dopant (SpiroAC–TRZ) is used to facilitate efficient energy transfer from host material poly(N–vinylcarbazole) (PVK) to a phosphorescent Ir(III) emitter. We present the analysis of energy transfer and charge trapping—two main processes playing a crucial role in light generation in host–guest structure OLEDs. The investigation of photo-, electro- and thermoluminescence for the double-dopant layer revealed that assistant dopant does not only harvest and transfer the electrically generated excitons to phosphorescent emitter molecules but also creates exciplexes. The triplet states of formed PVK:SpiroAC–TRZ exciplexes are involved in the transport process of charge carriers and promote long–range exciton energy transfer to the emitter, improving the efficiency of electroluminescence in a single emissive layer OLED, resulting in devices with luminance exceeding 18 000 cd/m2 with a luminous efficiency of 23 cd/A and external quantum efficiency (EQE) of 7.4%. Full article
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