Image-force effects on energy level alignment at electron transport material/cathode interfaces

Chen, Yongzhen; Liu, Xianjie; Wang, Ying; Fahlman, Mats

doi:10.1039/c9tc05128g

Cited by 16 publications

(17 citation statements)

References 54 publications

(57 reference statements)

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“…In addition to the above-mentioned four Phen derivatives, 4,7-di(9H-carbazol-9-yl)-1,10-phenanthroline (BUPH1) 36 , the ESP of which is smaller than that of BPhen, was used for comparison. Although there have been many reports on the electronic structure and the related interactions between a specific Phen derivative and several metals, there have been few reports on the interactions between several Phen derivatives and a specific metal 26 , 37 , 38 . Bin et al 30 were the first to use three Phen derivatives, and the p -MeO–Phen–Ag complex has been reported to be an excellent electron-injection layer (EIL).…”

Section: Resultsmentioning

confidence: 99%

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

Fukagawa¹,

Suzuki²,

Ito³

et al. 2020

Nat Commun

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The realisation of a cathode with various work functions (WFs) is required to maximise the potential of organic semiconductors that have various electron affinities. However, the barrier-free contact for electrons could only be achieved by using reactive materials, which significantly reduce the environmental stability of organic devices. We show that a stable electrode with various WFs can be produced by utilising the coordination reaction between several phenanthroline derivatives and the electrode. Although the low WF of the electrode realised by using reactive materials is specific to the material, the WF of the phenanthrolinemodified electrode is tunable depending on the amount of electron transfer associated with the coordination reaction. A phenanthroline-modified electrode that has a higher electron injection efficiency than lithium fluoride has been demonstrated. The observation of various WFs induced by the coordination reaction affords strategic perspectives on the development of stable cathodes unique to organic electronics.

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Section: Resultsmentioning

confidence: 99%

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

Fukagawa¹,

Suzuki²,

Ito³

et al. 2020

Nat Commun

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“…It has been recently found that certain organic semiconductor follows the ICT model with an extra displacement of the vacuum level. [ 99,100 ] Chen et al have studied the electrode–BPhen interface and found that the BPhen molecule follows the ICT model with an extra vacuum level shift of ≈1.4 eV. This shift was attributed to double dipole step formed at the interface.…”

Section: Energy‐level Alignment At Electrode–organic Interfacementioning

confidence: 99%

Interface Engineering in Organic Electronics: Energy‐Level Alignment and Charge Transport

2020

Small Science

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Organic light‐emitting diodes (OLEDs) and organic solar cells are new members of trillion‐dollar semiconductor industry. The structure of these devices generally consists of a stack of several organic layers sandwiched between two electrodes. The electronic processes such as the energy‐level alignment at and charge transport across these interfaces play a key role to the overall performance of the organic devices. Thus, interface physics is important for design and engineering of organic devices. Herein, recent progress in energy‐level alignment at and charge transport across organic interfaces is reviewed. In addition, basic material physics of organic semiconductors such as energy levels, energy disorder, and molecular orientation is introduced. Recent progress in theories and experiments on energy‐level alignment at and charge transport across molecular heterojunctions is then discussed. Case studies of applying interface physics for guiding fabrication of ideal devices are also provided.

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“…As a result, the interface dipole of B2PyMPM is reduced to the same level as that of B3 and B4PyMPM in the vacuum-deposited films. This is also the main reason that the interface dipole of B2PyMPM is much smaller than those of BPhen (−1.4 eV) and BCP (−1.6 eV), 18 , 23 even though the former is less affected by the hydrogen bonding.…”

Section: Results and Discussionmentioning

confidence: 97%

“…One dipole moment formed by the N nuclei and the lone pairs points from the substrate surface to the organic film and the other one formed by their image charges shows the same direction. 16 , 18 The N atoms far away from the substrate contribute little to the interface dipole.…”

Section: Results and Discussionmentioning

confidence: 99%

“… 20 , 21 Each molecule contains four pyridine substituents, in which N atoms with high electronegativity feature an in-plane lone pair of electrons on the sp 2 orbital. By comparing with the molecule BPhen, 18 we believe that BPyMPM should produce a similar interface dipole in contact with the electrode. In addition, for the vacuum-deposited films, it has been demonstrated that the molecular planes of B3PyMPM and B4PyMPM are oriented nearly parallel to the substrate surface due to the formation of intermolecular C–H···N hydrogen bonds in the films that facilitate molecular stacking.…”

Section: Introductionmentioning

confidence: 96%

See 1 more Smart Citation

Understanding Interface Dipoles at an Electron Transport Material/Electrode Modifier for Organic Electronics

Chen

Liu

Fahlman

2021

ACS Appl. Mater. Interfaces

Self Cite

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Interface dipoles formed at an electrolyte/electrode interface have been widely studied and interpreted using the “double dipole step” model, where the dipole vector is determined by the size and/or range of motion of the charged ions. Some electron transport materials (ETMs) with lone pairs of electrons on heteroatoms exhibit a similar interfacial behavior. However, the origin of the dipoles in such materials has not yet been explored in great depth. Herein, we systematically investigate the influence of the lone pair of electrons on the interface dipole through three pyridine derivatives B2–B4PyMPM. Experiments show that different positions of nitrogen atoms in the three materials give rise to different hydrogen bonds and molecular orientations, thereby affecting the areal density and direction of the lone pair of electrons. The interface dipoles of the three materials predicted by the “double dipole step” model are in good agreement with the ultraviolet photoelectron spectroscopy results both in spin-coated and vacuum-deposited films. These findings help to better understand the ETMs/electrode interfacial behaviors and provide new guidelines for the molecular design of the interlayer.

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Image-force effects on energy level alignment at electron transport material/cathode interfaces

Abstract: The work function of substrate can be sharply reduced by ETMs with an image-force induced double dipole.

Cited by 16 publications

References 54 publications

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

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

Interface Engineering in Organic Electronics: Energy‐Level Alignment and Charge Transport

Understanding Interface Dipoles at an Electron Transport Material/Electrode Modifier for Organic Electronics

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