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 organic/inorganic semiconductor heterojunctions: Fermi level pinning at the molecular interlayer with a reduced energy gap

2019 ◽  
Vol 21 (27) ◽  
pp. 15072-15079 ◽  
Author(s):  
Raphael Schlesinger ◽  
Stefanie Winkler ◽  
Matthias Brandt ◽  
Sylke Blumstengel ◽  
Ruslan Ovsyannikov ◽  
...  
Keyword(s):  
Energy Level ◽  
Fermi Level ◽  
Energy Gap ◽  
Fermi Level Pinning ◽  
Energy Level Alignment ◽  
Inorganic Semiconductor ◽  
Semiconductor Heterojunctions

A lying (L) molecular interlayer between ZnO and standing (S) sexiphenyl molecules leads to “concealed” Fermi level pinning.

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.

scholarly journals Molecular Structure and Antioxidant Properties of Alkali Metal Salts of Rosmarinic Acid. Experimental and DFT Studies

Molecules ◽  
2019 ◽  
Vol 24 (14) ◽  
pp. 2645 ◽  
Author(s):  
Renata Świsłocka ◽  
Ewa Regulska ◽  
Joanna Karpińska ◽  
Grzegorz Świderski ◽  
Włodzimierz Lewandowski
Keyword(s):  
Molecular Structure ◽  
Alkali Metal ◽  
Molecular Orbital ◽  
Rosmarinic Acid ◽  
Density Functional ◽  
Energy Gap ◽  
Antioxidant Properties ◽  
Reducing Power ◽  
Orbital Energy ◽  
Antioxidant Power

The molecular structure of alkali metal rosmarinates was studied in comparison to rosmarinic acid using FT-IR, FT-Raman, 1H and 13C NMR spectroscopy, as well as density functional theory (DFT) calculations. The B3LYP/6-311+G(d,p) method was used to calculate optimized geometrical structures of studied compounds, atomic charges, dipole moments, energies, as well as the wavenumbers and intensities of the bands in vibrational and NMR spectra. Theoretical parameters were compared to experimental data. Antioxidant activity was determined using two spectrophotometric methods: (i) Assessing the ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) stable radical and (ii) assay of antioxidant power of ferric ions reducing (FRAP). The linear correlations were found between HOMO–LUMO (highest occupied molecular orbital–lowest unoccupied molecular orbital) energy gap and the reducing power expressed as FRAP (R = 0.77) as well as between IC50 values (the ability of quenching DPPH radicals) and Δνas-s(COO) in IR spectra (differences between asymmetric and symmetric stretching vibrations bands) (R = 0.99). Photochemical properties of studied compounds were also evaluated. The influence of alkali metal on the electronic system of the rosmarinic acid molecule was discussed.

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.

A New Alternative for the Low-Workfunction Electrode in Organic Devices

1999 ◽  
Vol 598 ◽  
Author(s):  
Norbert Koch ◽  
Egbert Zojer ◽  
Aparna Rajagopal ◽  
Jacques Ghijsen ◽  
Robert L. Johnson ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Energy Level ◽  
Strong Interaction ◽  
Photoelectron Spectroscopy ◽  
Organic Material ◽  
Photoelectron Spectra ◽  
Covalent Bonds ◽  
Light Emitting ◽  
Energy Level Alignment ◽  
Organic Devices

ABSTRACTThe application of ele ctroactive organic materials in devices (light emitting diodes, photovoltaic cells) often requires electrodes with a low workfunction. Commonly, aluminum or alkaline earth metals are used, which usually exhibit strong interaction with the organic material, such as the formation of new covalent bonds or doping. This results in a strong modification of the electronic structure of the organic/metal interface, and in most cases does not yield the energy level alignment expected for the unreacted interface. As a n alternative to the above-mentioned metals we propose the use of samarium, with a workfunction of 2.7 eV, for the following reason: we have studied the interface formation between Sm and p -sexiphenyl (6P, which exhibits intense blue electroluminescence), with ultraviolet photoelectron spectroscopy. Sm was deposited stepwise onto thin films of 6P in ultrahigh vacuum, and the photoelectron spectra were recorded after each step. We did not find any indication for a strong interaction between the two materials. Metallic Sm is formed instantaneously and the valence electronic structure of 6P remains unchanged upon the metal deposition. The weak interaction at this interface allows one to determine the energy level alignment between a metal and an organic material in a direct manner from the photoelectron spectra, without the need for making any assumptions on the workfunction or ionization potential.

Room Temperature Alkali Metal Reduction of Carbon Dioxide

2020 ◽  
Author(s):  
Lucas A. Freeman ◽  
Akachukwu D. Obi ◽  
Haleigh R. Machost ◽  
Andrew Molino ◽  
Asa W. Nichols ◽  
...  
Keyword(s):  
Alkali Metal ◽  
Alkali Metals ◽  
Room Temperature ◽  
Chemical Reduction ◽  
Bond Cleavage ◽  
Open Shell ◽  
Metal Reduction ◽  
One Pot ◽  
Earth Abundant ◽  
Electron Reduction

The reduction of the relatively inert carbon–oxygen bonds of CO<sub>2</sub> to access useful CO<sub>2</sub>-derived organic products is one of the most important fundamental challenges in synthetic chemistry. Facilitating this bond-cleavage using earth-abundant, non-toxic main group elements (MGEs) is especially arduous because of the difficulty in achieving strong inner-sphere interactions between CO<sub>2</sub> and the MGE. Herein we report the first successful chemical reduction of CO<sub>2</sub> at room temperature by alkali metals, promoted by a cyclic(alkyl)(amino) carbene (CAAC). One-electron reduction of CAAC-CO<sub>2</sub> adduct (<b>1</b>) with lithium, sodium or potassium metal yields stable monoanionic radicals clusters [M(CAAC–CO<sub>2</sub>)]<sub>n</sub>(M = Li, Na, K, <b> 2</b>-<b>4</b>) and two-electron alkali metal reduction affords open-shell, dianionic clusters of the general formula [M<sub>2</sub>(CAAC–CO<sub>2</sub>)]<sub>n </sub>(<b>5</b>-<b>8</b>). It is notable that these crystalline clusters of reduced CO<sub>2</sub> may also be isolated via the “one-pot” reaction of free CO<sub>2</sub> with free CAAC followed by the addition of alkali metals – a reductive process which does not occur in the absence of carbene. Each of the products <b>2</b>-<b>8</b> were investigated using a combination of experimental and theoretical methods.<br>

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