Understanding coordination reaction for producing stable electrode with various low work functions

Fukagawa, Hirohiko; Suzuki, Kazuhiro; Ito, Hirokazu; Inagaki, Kaito; Sasaki, Tsubasa; Oono, Taku; Hasegawa, Munehiro; Morii, Katsuyuki; Shimizu, Takahisa

doi:10.1038/s41467-020-17548-z

Cited by 25 publications

(24 citation statements)

References 61 publications

(90 reference statements)

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“…Very recently, Tang et al have realised a low effective WF of 2.4 eV using multivalent anions 24 . Both Bin et al and the present authors reported some phenanthroline derivatives that can reduce the WF of electrodes to below 3 eV by utilising the coordination reaction from phenanthroline derivatives with metals 25,26 . We also demonstrated that the formation of hydrogen bonds (H-bonds) between nitrogen in bases and other organic semiconductors reduces the WF to about 3 eV 27 .…”

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confidence: 53%

“…The difference in WF between OLED-5 and OLED-1 (Δ co in Fig. 1d) originates from the coordination reaction 25,26 . In addition, the direct measurement of EA by LEIPS clarified that the coordination reaction also causes the change in the EA of F-Py from 2.16 to 2.80 eV (δ EA in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…The WF was further reduced to about 2.0 eV by utilising the coordination reaction when Al was deposited on this film (Supplementary Figs. 3 and 6, Supplementary Table 1) 25,26 . The importance of utilising both H-bonds and the coordination reaction can be seen from the characteristics of the OLED where hydrogen-free C 60 was employed in the ETL (Supplementary Fig.…”

Section: Resultsmentioning

confidence: 99%

“…We demonstrate that these typical ETMs are not essential for OLEDs by finding an EIL that can significantly reduce the work function (WF) around the cathode. The realisation of a low-WF electrode to eliminate reactive alkali elements from organic devices has been the subject of intense study 9,[23][24][25][26][27] . Zhou et al reported various low-WF electrodes with a minimum WF of 3.1 eV by utilising polyethyleneimine 23 .…”

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confidence: 99%

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Unravelling the electron injection/transport mechanism in organic light-emitting diodes

et al. 2021

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Although significant progress has been made in the development of light-emitting materials for organic light-emitting diodes along with the elucidation of emission mechanisms, the electron injection/transport mechanism remains unclear, and the materials used for electron injection/transport have been basically unchanged for more than 20 years. Here, we unravelled the electron injection/transport mechanism by tuning the work function near the cathode to about 2.0 eV using a superbase. This extremely low-work function cathode allows direct electron injection into various materials, and it was found that organic materials can transport electrons independently of their molecular structure. On the basis of these findings, we have realised a simply structured blue organic light-emitting diode with an operational lifetime of more than 1,000,000 hours. Unravelling the electron injection/transport mechanism, as reported in this paper, not only greatly increases the choice of materials to be used for devices, but also allows simple device structures.

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confidence: 53%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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Unravelling the electron injection/transport mechanism in organic light-emitting diodes

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“…Altogether, these results validate the paramount importance of coordinating ligands with high nucleophilicity. When preparing this manuscript, we noticed that Fukagawa et al 41 had studied the coordination reaction between phen ligands and Zn 2+ to modulate WFs of the ITO/ZnO electrode modified with a pristine layer of phen-type derivatives. It is noteworthy that in their research, p-Amn-phen also functioned as a good electron-injection layer in combination with ZnO, which is opposite to our present research findings, where Ag was used as the n-dopant, indicating a different working mechanism of their system.…”

Section: Discussionmentioning

confidence: 99%

Suppressing Competitive Coordination Reaction for Ohmic Cathode Contact Using Amino-Substituted Organic Ligands and Air-Stable Metals

et al. 2021

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Ohmic cathode contact can be formed readily via coordination-activated n-doping (CAN), by co-evaporating air-stable metals (e.g., silver) and organic ligands with coordination sites. It has been proposed that increasing the nucleophilicity of the main binding site of a ligand is essential for reducing the work function of the doped films. Here, engineering was conducted on phenanthroline-type ligands by introducing amino substitutes, which were stronger donors than MeO substitutes reported previously to increase the nucleophilicity of the ring nitrogen atoms binding-sites. Surprisingly, the dimethylamino group disabled the n-doping ability of silver via competitive coordination reaction with its sp 3 nitrogen. Cyclic amino substitutes are thereof adopted to tune the p orbital of the exocyclic nitrogen coplanar with the phenanthroline ring to enhance the conjugative effect to significantly promote the coordination ability of the ring nitrogen. The optimal ligand renders ohmic contact with an even low concentration of silver and also lowered the work functions of copper and gold for a more-readily released free electrons than cesium. Electron injection layers doped in this manner could efficiently introduce electrons into organic semiconductors, typically, with low electron affinity of ∼2.2 eV, and the corresponding red organic light-emitting diodes (OLEDs) showed enhanced efficiency with a record-long lifetime.

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Unlocking the Full Potential of Electron‐Acceptor Molecules for Efficient and Stable Hole Injection

et al. 2023

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Understanding the hole‐injection mechanism and improving the hole‐injection property are of pivotal importance in the future development of organic optoelectronic devices. Electron‐acceptor molecules with high electron affinity (EA) are widely used in electronic applications, such as hole injection and p‐doping. Although p‐doping has generally been studied in terms of matching the ionization energy (IE) of organic semiconductors with the EA of acceptor molecules, little is known about the effect of the EA of acceptor molecules on the hole‐injection property. In this work, the hole‐injection mechanism in devices is completely clarified, and a strategy to optimize the hole‐injection property of the acceptor molecule is developed. Efficient and stable hole injection is found to be possible even into materials with IEs as high as 5.8 eV by controlling the charged state of an acceptor molecule with an EA of about 5.0 eV. This excellent hole‐injection property enables direct hole injection into an emitting layer, realizing a pure blue organic light‐emitting diode with an extraordinarily low turn‐on voltage of 2.67 V, a power efficiency of 29 lm W−1, an external quantum efficiency of 28% and a Commission Internationale de l'Eclairage y coordinate of less than 0.10.

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Understanding coordination reaction for producing stable electrode with various low work functions

Cited by 25 publications

References 61 publications

Unravelling the electron injection/transport mechanism in organic light-emitting diodes

Unravelling the electron injection/transport mechanism in organic light-emitting diodes

Suppressing Competitive Coordination Reaction for Ohmic Cathode Contact Using Amino-Substituted Organic Ligands and Air-Stable Metals

Unlocking the Full Potential of Electron‐Acceptor Molecules for Efficient and Stable Hole Injection

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