Highly Efficient Blue Electroluminescence Using Delayed-Fluorescence Emitters with Large Overlap Density between Luminescent and Ground States

Katsuyuki Shizu, Hiroki Noda, Hiroyuki Tanaka, Masatsugu Taneda, Motoyuki Uejima, Tohru Sato, Kazuyoshi Tanaka, Hironori Kaji, Chihaya Adachi

Research output: Contribution to journalArticle

73 Citations (Scopus)

Abstract

The use of thermally activated delayed-fluorescence (TADF) allows the realization of highly efficient organic light-emitting diodes (OLEDs) and is a promising alternative to the use of conventional fluorescence and phosphorescence. Recent research interest has focused on blue TADF emitters. In this study, we use quantum mechanics to reveal the relationship between the molecular structures and the photophysical properties of TADF emitters and derive a direction for the molecular design of highly efficient blue TADF emitters. Theoretical analyses show that the luminescence efficiency of TADF emitters largely depends on the overlap density (ρ10) between the electronic wave functions of the ground state and the lowest excited singlet state. By increasing ρ10, we develop an efficient sky-blue TADF emitter material, 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (BCzT). When doped into a host layer, BCzT produces a high photoluminescence quantum yield of 95.6%. From the transient photoluminescence decays of the doped film, the efficiency of excited triplet state conversion into light is estimated to be 76.2%. An OLED using BCzT as a sky-blue emitter produces a maximum external quantum efficiency (EQE) of 21.7%, which is much higher than the EQE range of conventional fluorescent OLEDs (5-7.5%). The high EQE is a result of the high triplet-to-light conversion efficiency of BCzT. Our material design based on ρ10 distribution provides a rational approach for developing TADF emitters for high-efficiency blue OLEDs.

Original languageEnglish
Pages (from-to)26283-26289
Number of pages7
JournalJournal of Physical Chemistry C
Volume119
Issue number47
DOIs
Publication statusPublished - Nov 25 2015

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Electroluminescence
electroluminescence
Ground state
emitters
Fluorescence
fluorescence
ground state
Organic light emitting diodes (OLED)
light emitting diodes
Quantum efficiency
quantum efficiency
Excited states
sky
Photoluminescence
photoluminescence
Phosphorescence
Quantum theory
Quantum yield
phosphorescence
Wave functions

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

Cite this

Highly Efficient Blue Electroluminescence Using Delayed-Fluorescence Emitters with Large Overlap Density between Luminescent and Ground States. / Shizu, Katsuyuki; Noda, Hiroki; Tanaka, Hiroyuki; Taneda, Masatsugu; Uejima, Motoyuki; Sato, Tohru; Tanaka, Kazuyoshi; Kaji, Hironori; Adachi, Chihaya.

In: Journal of Physical Chemistry C, Vol. 119, No. 47, 25.11.2015, p. 26283-26289.

Research output: Contribution to journalArticle

Shizu, Katsuyuki ; Noda, Hiroki ; Tanaka, Hiroyuki ; Taneda, Masatsugu ; Uejima, Motoyuki ; Sato, Tohru ; Tanaka, Kazuyoshi ; Kaji, Hironori ; Adachi, Chihaya. / Highly Efficient Blue Electroluminescence Using Delayed-Fluorescence Emitters with Large Overlap Density between Luminescent and Ground States. In: Journal of Physical Chemistry C. 2015 ; Vol. 119, No. 47. pp. 26283-26289.
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AU - Tanaka, Hiroyuki

AU - Taneda, Masatsugu

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AU - Kaji, Hironori

AU - Adachi, Chihaya

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AB - The use of thermally activated delayed-fluorescence (TADF) allows the realization of highly efficient organic light-emitting diodes (OLEDs) and is a promising alternative to the use of conventional fluorescence and phosphorescence. Recent research interest has focused on blue TADF emitters. In this study, we use quantum mechanics to reveal the relationship between the molecular structures and the photophysical properties of TADF emitters and derive a direction for the molecular design of highly efficient blue TADF emitters. Theoretical analyses show that the luminescence efficiency of TADF emitters largely depends on the overlap density (ρ10) between the electronic wave functions of the ground state and the lowest excited singlet state. By increasing ρ10, we develop an efficient sky-blue TADF emitter material, 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9′-phenyl-9H,9′H-3,3′-bicarbazole (BCzT). When doped into a host layer, BCzT produces a high photoluminescence quantum yield of 95.6%. From the transient photoluminescence decays of the doped film, the efficiency of excited triplet state conversion into light is estimated to be 76.2%. An OLED using BCzT as a sky-blue emitter produces a maximum external quantum efficiency (EQE) of 21.7%, which is much higher than the EQE range of conventional fluorescent OLEDs (5-7.5%). The high EQE is a result of the high triplet-to-light conversion efficiency of BCzT. Our material design based on ρ10 distribution provides a rational approach for developing TADF emitters for high-efficiency blue OLEDs.

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