Molecular engineering versus energy level alignment: Interface formation between oligothiophene derivatives and a metal substrate studied with photoemission spectroscopy

2002 ◽  
Vol 91 (8) ◽  
pp. 5456-5461 ◽  
Author(s):  
A. J. Mäkinen ◽  
I. G. Hill ◽  
M. Kinoshita ◽  
T. Noda ◽  
Y. Shirota ◽  
...  
Keyword(s):  
Energy Level ◽  
Metal Substrate ◽  
Molecular Engineering ◽  
Photoemission Spectroscopy ◽  
Interface Formation ◽  
Energy Level Alignment

Interaction and Energy Level Alignment at Interfaces between Pentacene and Low Work Function Metals

2001 ◽  
Vol 708 ◽  
Author(s):  
N. Koch ◽  
J. Ghijsen ◽  
R. Ruiz ◽  
J. Pflaum ◽  
R. L. Johnson ◽  
...  
Keyword(s):  
Energy Level ◽  
Alkali Metal ◽  
Molecular Orbital ◽  
Organic Material ◽  
Alkali Metals ◽  
Energy Gap ◽  
Emission Feature ◽  
Photoemission Spectroscopy ◽  
Energy Level Alignment ◽  
A Charge

ABSTRACTA number of low workfunction metals (samarium, alkali metals) were deposited onto vacuum sublimed thin films of pentacene. The change in the valence electronic structure of the organic material was studied by in situ ultraviolet photoemission spectroscopy (UPS). Alkali metal intercalation leads to the appearance of a new photoemission feature within the pentacene energy gap, due to a charge transfer from the alkali atoms to the lowest unoccupied molecular orbital (LUMO) of the organic material. The energy spacing between this emission feature and the relaxed highest occupied molecular orbital (HOMO) of the pristine molecule is 1 eV. From X-ray photoemission spectroscopy core level analysis, we estimate a concentration ratio of two alkali metal atoms per pentacene molecule at maximum intercalation level, leading to a complete filling of the LUMO. This is consistent with the results from UPS that the new emission is always observed below the Fermi-level. Samarium is found to exhibit a more subtle interaction with pentacene: the molecular orbitals remain almost unperturbed upon Sm deposition. The resulting energy level alignment at this interface seems to be very favorable for the injection of electrons from Sm into pentacene, as the HOMO-onset is found at 1.8 eV below the metal Fermi edge. This value is close to the 2.2 eV HOMO-LUMO gap of pentacene measured by UPS and inverse photoemission spectroscopy, thus corresponding to a small electron injection barrier.

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

MRS Advances ◽  
2017 ◽  
Vol 2 (42) ◽  
pp. 2261-2266
Author(s):  
Kohei Shimizu ◽  
Hirohiko Fukagawa ◽  
Katsuyuki Morii ◽  
Hiroumi Kinjo ◽  
Tomoya Sato ◽  
...  
Keyword(s):  
Energy Level ◽  
Work Function ◽  
Indium Tin Oxide ◽  
Electron Injection ◽  
Photoemission Spectroscopy ◽  
Level Shift ◽  
Kelvin Probe ◽  
Vacuum Level ◽  
Energy Level Alignment ◽  
Improvement Effect

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.

Vapor Deposition of Perovskite Precursor PbI2 on Au and Graphite

MRS Advances ◽  
2020 ◽  
Vol 5 (8-9) ◽  
pp. 403-410
Author(s):  
Benjamin Ecker ◽  
Ke Wang ◽  
Yongli Gao
Keyword(s):  
Energy Level ◽  
Film Formation ◽  
Pyrolytic Graphite ◽  
Photoemission Spectroscopy ◽  
Photovoltaic Devices ◽  
Excessive Iodine ◽  
Energy Level Alignment ◽  
Perovskite Photovoltaic ◽  
Deposition Conditions

AbstractThe energy level alignment that occurs at the interfaces in planar-hetero structured perovskite photovoltaic devices strongly influences the charge transport across the interface, and thus plays a crucial role in overall device performance. To directly observe the energy level alignment requires pristine homogeneous surfaces that are free of contamination including adventitious carbon. Co-evaporation offers the ability to grow perovskite thin films in-situ, and the method involves thermally evaporating the perovskite precursors such as PbI2 and CH3NH3I. Early reports have shown that the perovskite film formation and stoichiometry are problematic at ultralow coverages. In particular, it was reported that there was excessive PbI2 and a deficiency in CH3NH3I. Using photoemission spectroscopy, we investigated the perovskite precursor PbI2 on gold and highly oriented pyrolytic graphite (HOPG) surfaces. Results show that the nature of the surface and the deposition conditions can strongly influence the film formation. Excessive iodine observed in the initial evaporation stages appears to be substrate dependent, and this may influence the overall energy level alignment.

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

2009 ◽  
Vol 1212 ◽  
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.

Energy Level Alignment at Fullerene/Phthalocyanine Interface Studied by Electron Spectroscopies

2003 ◽  
Vol 771 ◽  
Author(s):  
Hisao Ishii ◽  
Atsushi Seko ◽  
Akira Kawakami ◽  
Kazunori Umishita ◽  
Yukio Ouchi ◽  
...  
Keyword(s):  
Energy Level ◽  
Photovoltaic Cells ◽  
Energy Shift ◽  
Metal Electrode ◽  
Organic Photovoltaic ◽  
Level Shift ◽  
Organic Photovoltaic Cells ◽  
Interface Formation ◽  
Band Bending ◽  
Energy Level Alignment

AbstractInterfacial band offset and band bending of organic semiconductors are critical to understand and improve organic photovoltaic cells. In this study, the energy level alignment of fullerene(C60) / metal-free phthalocyanine (H2Pc) interface which is one of the model interfaces of organic photovoltaic cells has been investigated using UV and X-ray photoemissions. For both ‘H2Pc on C60’ and “C60 on H2Pc' interfaces, 0.3 eV downward energy level shift was observed in XPS at the interface formation. This energy shift is quite steep in contrast to the band bending observed for C60/metal interfaces in our previous study, where thickness of 500nm was required to achieve 0.21eV band bending to get Fermi level alignment between metal electrode and C60. To clarify the origin of the band bending, the effect of the insertion of C60-H2Pc co-deposited layer between C60 and H2Pc layers was also investigated. The result suggested that possible doping of H2Pc to C60 is not main origin of the observed energy shift. We also found that the vacuum level shift at H2Pc/C60 interface is strongly dependent on the deposition sequence of the interface formation.

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