Investigating HOMO Energy Levels of Terminal Emitters for Realizing High-Brightness and Stable TADF-Assisted Fluorescence Organic Light-Emitting Diodes

Yi Ting Lee; Chin Yiu Chan; Masaki Tanaka; Masashi Mamada; Umamahesh Balijapalli; Youichi Tsuchiya; Hajime Nakanotani; Takuji Hatakeyama; Chihaya Adachi

doi:10.1002/aelm.202001090

Investigating HOMO Energy Levels of Terminal Emitters for Realizing High-Brightness and Stable TADF-Assisted Fluorescence Organic Light-Emitting Diodes

Yi Ting Lee, Chin Yiu Chan, Masaki Tanaka, Masashi Mamada, Umamahesh Balijapalli, Youichi Tsuchiya, Hajime Nakanotani, Takuji Hatakeyama, Chihaya Adachi^*

^*Corresponding author for this work

Research output: Journal Publications and Reviews › RGC 21 - Publication in refereed journal › peer-review

81 Citations (Scopus)

Abstract

By simple modification of the functional groups on the boron–nitrogen-containing skeleton, the energy level of the highest occupied molecular orbital (E_HOMO) of emitters can be easily adjusted. Blue-emission derivatives are developed, which are capable of showing small full width at half maximums and high photoluminescence quantum yields. Blue thermally activated delayed fluorescence (TADF)-assisted fluorescence organic light-emitting diodes (TAF-OLEDs) based on two new emitters as the terminal emitter are fabricated, resulting in high external quantum efficiency (EQE) of up to 21.9%, high color purity, and high brightness (L_max = 63 777 cd m⁻²). By analyzing the transient electroluminescence spectra of the TAF-OLEDs, it is found that a smaller E_HOMO difference between TADF-assistant dopant (TADF-AD) and terminal emitter efficiently helps to decrease hole trapping inside the emitting layer, hence resulting in a lower efficiency rolloff and a longer operational device lifetime. TAF-OLEDs based on CzBNCz as a terminal emitter having the closest E_HOMO to that of TADF-AD show a maximum EQE of 21.9% together with a reduced efficiency rolloff (EQEs of 21.2% and 19.8% at 100 and 1000 cd m⁻², respectively). This research provides a designing principle for a terminal emitter in TAF-OLEDs with well-matched energy levels towards reaching the requirements of commercial displays. © 2021 Wiley-VCH GmbH

Original language	English
Article number	2001090
Journal	Advanced Electronic Materials
Volume	7
Issue number	4
Online published	12 Mar 2021
DOIs	https://doi.org/10.1002/aelm.202001090
Publication status	Published - Apr 2021
Externally published	Yes

Funding

This work was supported financially by the Program for Building Regional Innovation Ecosystems of the Ministry of Education, Culture, Sports, Science and Technology, Japan and Kyulux, Inc. The computation was mainly carried out using the computer facilities at Research Institute for Information Technology, Kyushu University. The authors also acknowledge Ms. Nozomi Nakamura and Ms. Keiko Kusuhara for their technical assistance with this research.

Research Keywords

hyperfluorescence
narrow emission
organic light-emitting diodes
thermally activated delayed fluorescence

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Lee, Y. T., Chan, C. Y., Tanaka, M., Mamada, M., Balijapalli, U., Tsuchiya, Y., Nakanotani, H., Hatakeyama, T., & Adachi, C. (2021). Investigating HOMO Energy Levels of Terminal Emitters for Realizing High-Brightness and Stable TADF-Assisted Fluorescence Organic Light-Emitting Diodes. Advanced Electronic Materials, 7(4), Article 2001090. https://doi.org/10.1002/aelm.202001090

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title = "Investigating HOMO Energy Levels of Terminal Emitters for Realizing High-Brightness and Stable TADF-Assisted Fluorescence Organic Light-Emitting Diodes",

abstract = "By simple modification of the functional groups on the boron–nitrogen-containing skeleton, the energy level of the highest occupied molecular orbital (EHOMO) of emitters can be easily adjusted. Blue-emission derivatives are developed, which are capable of showing small full width at half maximums and high photoluminescence quantum yields. Blue thermally activated delayed fluorescence (TADF)-assisted fluorescence organic light-emitting diodes (TAF-OLEDs) based on two new emitters as the terminal emitter are fabricated, resulting in high external quantum efficiency (EQE) of up to 21.9%, high color purity, and high brightness (Lmax = 63 777 cd m−2). By analyzing the transient electroluminescence spectra of the TAF-OLEDs, it is found that a smaller EHOMO difference between TADF-assistant dopant (TADF-AD) and terminal emitter efficiently helps to decrease hole trapping inside the emitting layer, hence resulting in a lower efficiency rolloff and a longer operational device lifetime. TAF-OLEDs based on CzBNCz as a terminal emitter having the closest EHOMO to that of TADF-AD show a maximum EQE of 21.9% together with a reduced efficiency rolloff (EQEs of 21.2% and 19.8% at 100 and 1000 cd m−2, respectively). This research provides a designing principle for a terminal emitter in TAF-OLEDs with well-matched energy levels towards reaching the requirements of commercial displays. {\textcopyright} 2021 Wiley-VCH GmbH",

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author = "Lee, {Yi Ting} and Chan, {Chin Yiu} and Masaki Tanaka and Masashi Mamada and Umamahesh Balijapalli and Youichi Tsuchiya and Hajime Nakanotani and Takuji Hatakeyama and Chihaya Adachi",

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Investigating HOMO Energy Levels of Terminal Emitters for Realizing High-Brightness and Stable TADF-Assisted Fluorescence Organic Light-Emitting Diodes. / Lee, Yi Ting; Chan, Chin Yiu; Tanaka, Masaki et al.
In: Advanced Electronic Materials, Vol. 7, No. 4, 2001090, 04.2021.

Research output: Journal Publications and Reviews › RGC 21 - Publication in refereed journal › peer-review

TY - JOUR

T1 - Investigating HOMO Energy Levels of Terminal Emitters for Realizing High-Brightness and Stable TADF-Assisted Fluorescence Organic Light-Emitting Diodes

AU - Lee, Yi Ting

AU - Chan, Chin Yiu

AU - Tanaka, Masaki

AU - Mamada, Masashi

AU - Balijapalli, Umamahesh

AU - Tsuchiya, Youichi

AU - Nakanotani, Hajime

AU - Hatakeyama, Takuji

AU - Adachi, Chihaya

PY - 2021/4

Y1 - 2021/4

N2 - By simple modification of the functional groups on the boron–nitrogen-containing skeleton, the energy level of the highest occupied molecular orbital (EHOMO) of emitters can be easily adjusted. Blue-emission derivatives are developed, which are capable of showing small full width at half maximums and high photoluminescence quantum yields. Blue thermally activated delayed fluorescence (TADF)-assisted fluorescence organic light-emitting diodes (TAF-OLEDs) based on two new emitters as the terminal emitter are fabricated, resulting in high external quantum efficiency (EQE) of up to 21.9%, high color purity, and high brightness (Lmax = 63 777 cd m−2). By analyzing the transient electroluminescence spectra of the TAF-OLEDs, it is found that a smaller EHOMO difference between TADF-assistant dopant (TADF-AD) and terminal emitter efficiently helps to decrease hole trapping inside the emitting layer, hence resulting in a lower efficiency rolloff and a longer operational device lifetime. TAF-OLEDs based on CzBNCz as a terminal emitter having the closest EHOMO to that of TADF-AD show a maximum EQE of 21.9% together with a reduced efficiency rolloff (EQEs of 21.2% and 19.8% at 100 and 1000 cd m−2, respectively). This research provides a designing principle for a terminal emitter in TAF-OLEDs with well-matched energy levels towards reaching the requirements of commercial displays. © 2021 Wiley-VCH GmbH

AB - By simple modification of the functional groups on the boron–nitrogen-containing skeleton, the energy level of the highest occupied molecular orbital (EHOMO) of emitters can be easily adjusted. Blue-emission derivatives are developed, which are capable of showing small full width at half maximums and high photoluminescence quantum yields. Blue thermally activated delayed fluorescence (TADF)-assisted fluorescence organic light-emitting diodes (TAF-OLEDs) based on two new emitters as the terminal emitter are fabricated, resulting in high external quantum efficiency (EQE) of up to 21.9%, high color purity, and high brightness (Lmax = 63 777 cd m−2). By analyzing the transient electroluminescence spectra of the TAF-OLEDs, it is found that a smaller EHOMO difference between TADF-assistant dopant (TADF-AD) and terminal emitter efficiently helps to decrease hole trapping inside the emitting layer, hence resulting in a lower efficiency rolloff and a longer operational device lifetime. TAF-OLEDs based on CzBNCz as a terminal emitter having the closest EHOMO to that of TADF-AD show a maximum EQE of 21.9% together with a reduced efficiency rolloff (EQEs of 21.2% and 19.8% at 100 and 1000 cd m−2, respectively). This research provides a designing principle for a terminal emitter in TAF-OLEDs with well-matched energy levels towards reaching the requirements of commercial displays. © 2021 Wiley-VCH GmbH

KW - hyperfluorescence

KW - narrow emission

KW - organic light-emitting diodes

KW - thermally activated delayed fluorescence

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U2 - 10.1002/aelm.202001090

DO - 10.1002/aelm.202001090

M3 - RGC 21 - Publication in refereed journal

AN - SCOPUS:85102388053

SN - 2199-160X

VL - 7

JO - Advanced Electronic Materials

JF - Advanced Electronic Materials

IS - 4

M1 - 2001090

ER -

Investigating HOMO Energy Levels of Terminal Emitters for Realizing High-Brightness and Stable TADF-Assisted Fluorescence Organic Light-Emitting Diodes

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Research Keywords

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