Organic Luminescent Molecule with Energetically Equivalent Singlet and Triplet Excited States for Organic Light-Emitting Diodes

Sato, Keigo; Shizu, Katsuyuki; Yoshimura, Kazuaki; Kawada, Atsushi; Miyazaki, Hiroshi; Adachi, Chihaya

doi:10.1103/physrevlett.110.247401

Cited by 215 publications

(159 citation statements)

References 28 publications

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“…Other TADF emitters with near perpendicular D‐A structure have been reported recently with slightly different molecular structures 19. However, in most of these molecules lower device efficiencies have been obtained, when compared with the EQEs that are achieved with DPTZ‐DBTO2 devices.…”

Section: Discussionmentioning

confidence: 99%

The Role of Local Triplet Excited States and D‐A Relative Orientation in Thermally Activated Delayed Fluorescence: Photophysics and Devices

et al. 2016

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Here, a comprehensive photophysical investigation of a the emitter molecule DPTZ‐DBTO2, showing thermally activated delayed fluorescence (TADF), with near‐orthogonal electron donor (D) and acceptor (A) units is reported. It is shown that DPTZ‐DBTO2 has minimal singlet–triplet energy splitting due to its near‐rigid molecular geometry. However, the electronic coupling between the local triplet (3LE) and the charge transfer states, singlet and triplet, (1CT, 3CT), and the effect of dynamic rocking of the D–A units about the orthogonal geometry are crucial for efficient TADF to be achieved. In solvents with low polarity, the guest emissive singlet 1CT state couples directly to the near‐degenerate 3LE, efficiently harvesting the triplet states by a spin orbit coupling charge transfer mechanism (SOCT). However, in solvents with higher polarity the emissive CT state in DPTZ‐DBTO2 shifts below (the static) 3LE, leading to decreased TADF efficiencies. The relatively large energy difference between the 1CT and 3LE states and the extremely low efficiency of the 1CT to 3CT hyperfine coupling is responsible for the reduction in TADF efficiency. Both the electronic coupling between 1CT and 3LE, and the (dynamic) orientation of the D–A units are thus critical elements that dictate reverse intersystem crossing processes and thus high efficiency in TADF.

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Section: Discussionmentioning

confidence: 99%

The Role of Local Triplet Excited States and D‐A Relative Orientation in Thermally Activated Delayed Fluorescence: Photophysics and Devices

et al. 2016

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“…16 Up to now, the main picure that has arisen to explain the TADF mechanism involves the interconversion between 3 CT and 1 CT states. [2][3][4][5][6] However, more recently Monkman and co.…”

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confidence: 99%

Dynamic nature of excited states of donor–acceptor TADF materials for OLEDs: how theory can reveal structure–property relationships

et al. 2017

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“…[17][18][19] Therefore, it would be important to understand how a TADF fluorophor would perform in the presence of a phosphorescent EHA perturber.…”

Section: Introductionmentioning

confidence: 99%

Highly efficient hybrid warm white organic light-emitting diodes using a blue thermally activated delayed fluorescence emitter: exploiting the external heavy-atom effect

et al. 2015

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To attain high efficiencies in hybrid white organic light-emitting diodes (WOLEDs), mutual quenching of the fluorophors and phosphors should be minimized. Efforts have been devoted to reducing the triplet quenching of phosphors; however, the quenching of fluorophors by the external heavy-atom effect (EHA) introduced by the phosphors is often ignored. Here, we observed that conventional fluorophors and fluorophors with thermally activated delayed fluorescence (TADF) behave differently in the presence of EHA perturbers. The efficiencies of the conventional fluorophors suffer greatly from the EHA, whereas the TADF fluorophors exhibit negligible changes, which makes TADF materials ideal fluorophors for hybrid devices. WOLEDs using a blue TADF fluorophor and an orange phosphor achieve a maximum forward viewing external quantum efficiency of 19.6% and a maximum forward viewing power efficiency of 50.2 lm W 21 , among the best values for hybrid WOLEDs. This report is the first time that the EHA effect has been considered in hybrid WOLEDs and that a general strategy toward highly efficient hybrid WOLEDs with simple structures is proposed. Keywords: external heavy-atom effect; hybrid white OLEDs; thermally activated delayed fluorescence INTRODUCTION Recent conceptual advancements have led to many exciting approaches to white organic light-emitting diodes (WOLEDs). 1-4 For practical use, high efficiency and long lifetime are the most critical parameters. Blue phosphors can obtain high luminous efficiency but suffer from short lifetime, while blue fluorophors are exactly the opposite. 5,6 Efforts have been devoted to resolve the tradeoff between the high efficiency and long lifetime by combining the advantages of phosphors and fluorophors, that is, by fabricating hybrid WOLEDs with blue fluorophors and green/red or orange phosphors. [6][7][8][9] To attain high efficiencies in hybrid WOLEDs, mutual quenching of the fluorophors and phosphors should be minimized. It has been long realized that the quenching of the green and red phosphorescence by the low triplet energy fluorophors is one of the main losses of excitation energy in these devices. 6 Therefore, a 'triplet harvesting' strategy by doping a blue fluorophor and red/green phosphors in separated regions of high-triplet-energy host materials has been proposed 1,10 and is further improved by incorporating blue fluorophors with high triplet energy (T 1 ) to prevent the undesirable 'back energy transfer' from the phosphors to the blue fluorophors. 2,7,8 However, the heavy metal in the phosphors introduce an external heavy-atom effect (EHA) in the emissive layer (EML) and may lead to

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Organic Luminescent Molecule with Energetically Equivalent Singlet and Triplet Excited States for Organic Light-Emitting Diodes

Cited by 215 publications

References 28 publications

The Role of Local Triplet Excited States and D‐A Relative Orientation in Thermally Activated Delayed Fluorescence: Photophysics and Devices

The Role of Local Triplet Excited States and D‐A Relative Orientation in Thermally Activated Delayed Fluorescence: Photophysics and Devices

Dynamic nature of excited states of donor–acceptor TADF materials for OLEDs: how theory can reveal structure–property relationships

Highly efficient hybrid warm white organic light-emitting diodes using a blue thermally activated delayed fluorescence emitter: exploiting the external heavy-atom effect

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