Title: Host-Free Yellow-Green Organic Light-Emitting Diodes with External Quantum Efficiency over 20% Based on a Compound Exhibiting Thermally Activated Delayed Fluorescence

Abstract

Thermally activated delayed fluorescent (TADF) materials are advantageous as emitters in organic light-emitting diodes (OLEDs) due to their ability to utilize all excited states formed by charge recombination for light emission, potentially leading to 100% internal quantum efficiency. As in conventional fluorescent or phosphorescent OLEDs, TADF emitters are commonly doped at a relatively low concentration in a host matrix. However, increasing evidence suggest that balanced ambipolar transport properties and small aggregation-induced fluorescence quenching allows TADF emitters to be used alone in so-called host-free OLEDs. Here, we report on host-free OLEDs in which the EMLs consist solely of a yellow-green-emitting TADF compound, 5,5'-(2,3,5,6-tetra(carbazol-9-yl)-1,4-phenylene)bis(2-(4-(tert-butyl)phenyl)-1,3,4-oxadiazole), TCZPBOX. Devices with this host-free EML yield a maximum external quantum efficiency (EQE) of 21%, current efficacy (CE) of 73 cd/A, and power efficacy (PE) of 79 lm/W at a luminance of 10 cd/m². At a high luminance of 10,000 cd/m², a high EQE of 13% is maintained. A maximum luminance of 120,000 cd/m2 is reached at an applied voltage of 9.8 V. When TCZPBOX was doped in the host of 2,6-di(carbazol-9-yl)-pyridine (PYD2) at 40 wt. %, the device yielded a maximum EQE of 28%, CE of 94 cd/A, and PE of 100 lm/W at 10 cd/m².

Authors:

Zhang, Xiaoqing  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-1930-623X"

Cooper, Matthew W.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-3589-8688"

Zhang, Yadong ^[1]; Fuentes-Hernandez, Canek  ^[1];

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Barlow, Stephen  ^[1];

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Marder, Seth R.  ^[1];

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• Search DOE PAGES for ORCID "0000-0001-6921-2536"

Kippelen, Bernard  ^[1]

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• Search DOE PAGES for ORCID "0000-0002-8417-7051"

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+ Show Author Affiliations

1. Georgia Inst. of Technology, Atlanta, GA (United States)

Publication Date:

Tue Mar 05 00:00:00 EST 2019

Research Org.:

Georgia Institute of Technology, Atlanta, GA (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE)

OSTI Identifier:

1767165

Grant/Contract Number:  

EE0008205

Resource Type:

Accepted Manuscript

Journal Name:

ACS Applied Materials and Interfaces

Additional Journal Information:

Journal Volume: 11; Journal Issue: 13; Journal ID: ISSN 1944-8244

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; Solid state lighting; light-emitting diodes; organic light-emitting diode; thermally activated delayed fluorescence; guest−host systems; host-free emissive layers; concentration quenching; thin films; external quantum efficiency; fluorescence; aromatic compounds