Energy Level Alignment at Bebq2/PEI/ITO Interfaces Studied by UV Photoemission Spectroscopy

ABSTRACTA polyethyleneimine (PEI) interlayer has been applied on indium tin oxide (ITO) to improve electron injection in organic devices including inverted organic light-emitting diodes (OLEDs). To understand the improvement effect by PEI insertion, the energy level alignment at bis(10-hydroxybenzo[h]quinolinato)beryllium (Bebq2)/PEI/ITO interfaces was investigated by UV photoemission spectroscopy (UPS). The deposition of a PEI layer was found to reduce the absolute work function of ITO by 1.4 eV. The vacuum level shifts at Bebq2/ITO and Bebq2/PEI interfaces were also determined as 0.3 eV and 0.1 eV in the direction to reduce the electron injection barrier, respectively. Thus the work function reduction by PEI and downward vacuum level shift at the Bebq2/PEI interface can contribute to the improvement effect. Kelvin probe measurement revealed the weak orientation polarization in Bebq2 film with the bottom side positively polarized. This polarization polarity is also advantageous for electron injection in inverted devices.

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Direct comparison of photoemission spectroscopy and in situ Kelvin probe work function measurements on indium tin oxide films

Journal of Electron Spectroscopy and Related Phenomena ◽

10.1016/j.elspec.2006.02.001 ◽

2006 ◽

Vol 152 (1-2) ◽

pp. 12-17 ◽

Cited By ~ 79

Author(s):

M.M. Beerbom ◽

B. Lägel ◽

A.J. Cascio ◽

B.V. Doran ◽

R. Schlaf

Keyword(s):

Work Function ◽

Tin Oxide ◽

Indium Tin Oxide ◽

Oxide Films ◽

Photoemission Spectroscopy ◽

Kelvin Probe ◽

Tin Oxide Films

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UV Photoemission Study of Interfaces Related to Organic EL Devices

MRS Proceedings ◽

10.1557/proc-488-719 ◽

1997 ◽

Vol 488 ◽

Cited By ~ 2

Author(s):

Kiyoshi Sugiyama ◽

Kazuhiko Seki ◽

Eisuke Ito ◽

Yukio Ouchi ◽

Hisao ISHII

Keyword(s):

Tin Oxide ◽

Indium Tin Oxide ◽

Electronic Structures ◽

Organic Molecule ◽

Negative Charge ◽

Photoemission Spectroscopy ◽

Level Shift ◽

Vacuum Level ◽

Organic Electroluminescent ◽

Photoemission Study

AbstractInterfacial electronic structures related to organic electroluminescent (EL) devices were studied by UV photoemission spectroscopy (UPS). The two classes of interfaces studied were: (1) interfaces in a typical multilayer device AI/AIq3TPD/ITO, where Alq3 is tris(8-hydroxyquinolino)- aluminum, TPD is N,N×-diphenyl-NN×-(3-methylphenyl)- 1, 1‘-biphenyl-4,4’-diamine, and ITO is indium tin oxide, and (2) TTN/metals and TCNQ/metals interfaces, where TTN is tetrathianaphthacene and TCNQ is tetracyanoquinodimethane. The UPS studies of the specimen formed by the successive deposition of TPD, Alq3, and Al on ITO revealed interfacial energy diagrams, with the vacuum level shift of - 0.25 eV (downward) and - 0.1 eV (downward) at the TPD / ITO and the Alq3 / TPD interfaces, respectively. The deposition of TTN and TCNQ on metals showed opposite direction of the shift of the vacuum level, with the positive and negative charge at the vacuum side. This can be explained by considering the chargetransfer between the metal and the organic molecule, with these directions being consistent with the electron donating and accepting ability of these molecules.

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The effect of molybdenum trioxide inter-layer between indium tin oxide (ITO) and organic semiconductor on the energy level alignment

MRS Proceedings ◽

10.1557/proc-1212-s08-05 ◽

2009 ◽

Vol 1212 ◽

Cited By ~ 1

Author(s):

Irfan Irfan ◽

Huanjun Ding ◽

Yongli Gao ◽

Do Yang Kim ◽

Jegadesan Subbiah ◽

...

Keyword(s):

Energy Level ◽

Tin Oxide ◽

Indium Tin Oxide ◽

Molybdenum Trioxide ◽

Ultra Violet ◽

Photoemission Spectroscopy ◽

Layer By Layer ◽

Band Bending ◽

Energy Level Alignment ◽

In Series

AbstractWe investigated 0 to 300 Å thick stepped molybdenum trioxide (MoO3) inter-layer between in-situ oxygen plasma treated conducting indium tin oxide (ITO) and chloro-aluminum pthalocyanine (AlPc-Cl) layer-by-layer evaporated up to 228 Å, with ultra-violet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPES). The MoO3 inter-layers were observed to increase the surface workfunction. The workfunction increase was observed to saturate at 20 Å of MoO3 coverage. The increased surface workfunction causes hole accumulation and band bending in the subsequently deposited AlPc-Cl. A possible explanation of reduction in series resistance by the insertion of the MoO3 insulating layer is discussed based on these observations and energy level alignment.

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Energy-Level Alignment at Interfaces between Transition-Metal Dichalcogenide Monolayers and Metal Electrodes Studied with Kelvin Probe Force Microscopy

The Journal of Physical Chemistry C ◽

10.1021/acs.jpcc.1c01612 ◽

2021 ◽

Author(s):

Pavel A. Markeev ◽

Emad Najafidehaghani ◽

Ziyang Gan ◽

Kai Sotthewes ◽

Antony George ◽

...

Keyword(s):

Transition Metal ◽

Energy Level ◽

Kelvin Probe Force Microscopy ◽

Transition Metal Dichalcogenide ◽

Kelvin Probe ◽

Metal Electrodes ◽

Force Microscopy ◽

Energy Level Alignment

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Energy Level Alignment at the Metal/Alq3 Interfaces Investigated with Photoemission Methods

MRS Proceedings ◽

10.1557/proc-660-jj8.36 ◽

2000 ◽

Vol 660 ◽

Author(s):

Li Yan ◽

C.W. Tang ◽

M. G. Mason ◽

Yongli Gao

Keyword(s):

Energy Level ◽

Work Function ◽

Photoelectron Spectroscopy ◽

Light Emission ◽

Electron Injection ◽

Core Level ◽

Material Research ◽

Level Shifts ◽

Key Issues ◽

Injection Materials

ABSTRACTTris(8-hydroxyquinoline) aluminum (Alq3) based organic light emission diodes (OLED) have been a focus of material research in recent years. One of the key issues in searching for a better device performance and fabricating conditions is suitable electron-injection materials. We have investigated the energy alignment and the interface formation between different metals and Alq3 using X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS). The interface is formed by depositing the target cathode material, such as Ca, Al or Al/LiF, onto an Alq3 film in a stepwise fashion in an ultrahigh vacuum environment. While the UPS results show the work function and vacuum level changes during interfaces formation, implying a possible surface dipole layer, XPS results show a more detailed and complex behavior. When a low work function metal such as Ca is deposited onto an Alq3 surface, a gap state is observed in UPS. At the same time, a new peak can be observed in the N 1s core level at a lower binding energy. These results can be characterized as charge transfer from the low work function metal to Alq3. The shifting of core levels are also observed, which may be explained by doping from metal atoms or charge diffusion. These interfaces are drastically different than the Al/Alq3 interface, which has very poor electron injection. At the Al/Alq3 interface there is a destructive chemical reaction and much smaller core level shifts are observed. Based on detailed analysis, energy level diagrams at the interface are proposed.

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