Energy-level alignment at model interfaces of organic electroluminescent devices studied by UV photoemission: trend in the deviation from the traditional way of estimating the interfacial electronic structures

Ishii, Hisao; Sugiyama, K.; Yoshimura, Daisuke; Ito, Eisuke; Ouchi, Yukio; Seki, Kazuhiko

doi:10.1109/2944.669459

Cited by 121 publications

(88 citation statements)

References 26 publications

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“…LiF has the advantage that it can be vacuum-deposited over large areas, using thermal evaporation. It is a standard material used to achieve a vacuum level shift of up to 1 eV in OLED devices 18,19 , via the electric dipole moment that develops as a result of the termination of the polar material at the interfaces. In our LE-μSR experiment, two devices were measured with an active area of 16×16 mm, comprising FeCo 17 nm/Alq 3 150 nm/LiF 1 nm/NiFe 20 nm (sample A) and FeCo 17 nm/Alq 3 150 nm/NiFe 20 nm (sample B).…”

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confidence: 99%

Engineering spin propagation across a hybrid organic/inorganic interface using a polar layer

et al. 2010

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Spintronics has shown a remarkable and rapid development, for example from the initial discovery of giant magnetoresistance in spin valves 1 to their ubiquity in hard-disk read heads in a relatively short time. However, the ability to fully harness electron spin as another degree of freedom in semiconductor devices has been slower to take off. One future avenue that may expand the spintronic technology base is to take advantage of the flexibility intrinsic to organic semiconductors (OSCs), where it is possible to engineer and control their electronic properties and tailor them to obtain new device concepts 2 . Here we show that we can control the spin polarization of extracted charge carriers from an OSC by the inclusion of a thin interfacial layer of polar material. The electric dipole moment brought about by this layer shifts the OSC highest occupied molecular orbital with respect to the Fermi energy of the ferromagnetic contact. This approach allows us full control of the spin band appropriate for charge-carrier extraction, opening up new spintronic device concepts for future exploitation.The development and understanding of new hybrid organic/inorganic interfaces will enable considerable progress in organic spintronics for technological purposes, including processing elements, sensors, memories and conceptually different future applications. In addition to the 'standard' spintronic applications, newly developed interfaces could bring spintronic effects to the field of organic light-emitting diodes (OLEDs), as well as in the fast progressing field of organic field-effect transistors. For example, the injection of carriers with a controlled spin state could enable the amplification of either singlet or triplet exciton states 2 leading to a significant increase in the efficiency of the electroluminescence in OLEDs. Although these considerations are conceptually straightforward, no efficiency amplification has yet been reported in the literature, despite several attempts 3 . The failure of those approaches was caused by the simple reason that light emission can be detected starting from an applied voltage of a few volts, whereas state-of-the-art spin injection in organic materials persists to a maximum of around 1 V (refs 4-6). As yet, this is unexplained. Further complications arise from the fact that various reports on working devices show a wide spread of performances for apparently similar structures, highlighting the issue of reproducibility [7][8][9] . The poor reproducibility is mainly due to the unknown interplay between processing and spin transfer performance and there is little deterministic control of the interface properties. However, it has recently been demonstrated that the insertion of a barrier

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confidence: 99%

Engineering spin propagation across a hybrid organic/inorganic interface using a polar layer

et al. 2010

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“…9. UPS spectra of TPD incrementally deposited on Au substrate as a function of film thickness [78,81]. The shift of the left-hand cutoff corresponds to the VL shift D in Figure 8.…”

Section: Organic-on-metal Interfacesmentioning

confidence: 99%

Energy Level Alignment and Interfacial Electronic Structures at Organic/Metal and Organic/Organic Interfaces

et al. 1999

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The function of electronically functional organic materials often originates at an interface, one example being organic electroluminescent devices (the Figure shows a typical energy diagram). Therefore, elucidation of the electronic structure at interfaces will lead to a better understanding of these devices, enabling their performance to be improved. Basic concepts are reexamined and recent progress in the area is reviewed.

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“…Therefore, the electronic properties of HMOS, as the band gap or the work function ( ), can be modulated by controlling the electrostatics at the interface. This feature opens the possibility to explore new functionalities in organic electronic devices [5] and to improve their performances [3,6].…”

Section: Introductionmentioning

confidence: 99%

Electronic charge rearrangement at metal/organic interfaces induced by weak van der Waals interactions

Ferri

Ambrosetti

Tkatchenko

2017

Phys. Rev. Materials

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Electronic charge rearrangements at interfaces between organic molecules and solid surfaces play a key role in a wide range of applications in catalysis, light-emitting diodes, single-molecule junctions, molecular sensors and switches, and photovoltaics. It is common to utilize electrostatics and Pauli pushback to control the interface electronic properties, while the ubiquitous van der Waals (vdW) interactions are often considered to have a negligible direct contribution (beyond the obvious structural relaxation). Here, we apply a fully self-consistent Tkatchenko-Scheffler vdW density functional to demonstrate that the weak vdW interactions can induce sizable charge rearrangements at hybrid metal/organic systems (HMOS). The complex vdW correlation potential smears out the interfacial electronic density, thereby reducing the charge transfer in HMOS, changes the interface work functions by up to 0.2 eV, and increases the interface dipole moment by up to 0.3 Debye. Our results suggest that vdW interactions should be considered as an additional control parameter in the design of hybrid interfaces with the desired electronic properties.

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Energy-level alignment at model interfaces of organic electroluminescent devices studied by UV photoemission: trend in the deviation from the traditional way of estimating the interfacial electronic structures

Cited by 121 publications

References 26 publications

Engineering spin propagation across a hybrid organic/inorganic interface using a polar layer

Engineering spin propagation across a hybrid organic/inorganic interface using a polar layer

Energy Level Alignment and Interfacial Electronic Structures at Organic/Metal and Organic/Organic Interfaces

Electronic charge rearrangement at metal/organic interfaces induced by weak van der Waals interactions

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