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Open AccessArticle

Towards Highly Efficient TADF Yellow-Red OLEDs Fabricated by Solution Deposition Methods: Critical Influence of the Active Layer Morphology

by Manish Kumar 1,2 and Luiz Pereira 1,*
1
Department of Physics and i3N—Institute for Nanostructures, Nanomodulation and Nanofabrication, University of Aveiro, 3810-193 Aveiro, Portugal
2
CeNTI—Centre for Nanotechnologies and Smart Materials, R. Fernando Mesquita, 2785, 4760-034 Vila Nova de Famalicão, Portugal
*
Author to whom correspondence should be addressed.
Nanomaterials 2020, 10(1), 101; https://doi.org/10.3390/nano10010101
Received: 22 November 2019 / Revised: 21 December 2019 / Accepted: 2 January 2020 / Published: 4 January 2020
(This article belongs to the Section Nanophotonics, Characterization, Modelling, and Nanodevices)
Organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence emitters (TADF) in simple device structures fabricated by solution processing are strongly dependent on a suitable host molecular conformation and morphology. Herein, we report the fabrication of highly efficient yellow-red TADF-based OLEDs via solution processing in a simple, two-organic-layer device structure. The devices were fabricated at different weight concentrations of 5%, 8%, and 10% emitter in an n-/p-type mixed host matrix, and their characteristics were studied. The device performance was compared with different thickness parameters for both the emitting layer (EML) and the electron transport layer (ETL) in various solvents, including chlorobenzene, dichlorobenzene, and chloroform. By optimizing the mixed ratio of EML, yellow-red OLEDs of 2-[4 (diphenylamino)phenyl]-10,10-dioxide-9H-thioxanthen-9-one (TXO-TPA) emitter in an n-/p-type host matrix of poly(N-vinylcarbazole):1,3-Bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazo-5-yl]benzene (PVK:OXD-7) as a blend for the active layer were fabricated. In the best results, the device exhibited a lower turn-on voltage at around 6 V, with an external quantum efficiency (EQE) of 18.44%, current efficiency of 36.71 cd/A, and power efficiency of 14.74 Lm/W for the 8% emitter concentration. The importance of solvent for improving the electrical properties, together with organic layer thickness and host effect for the charge carrier’s transport and device characteristics are also discussed. View Full-Text
Keywords: solution-processed OLEDs; TADF; morphology; electrical transport improvement; efficiency solution-processed OLEDs; TADF; morphology; electrical transport improvement; efficiency
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MDPI and ACS Style

Kumar, M.; Pereira, L. Towards Highly Efficient TADF Yellow-Red OLEDs Fabricated by Solution Deposition Methods: Critical Influence of the Active Layer Morphology. Nanomaterials 2020, 10, 101.

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