Electrode Work Function Engineering with Phosphonic Acid Monolayers and Molecular Acceptors: Charge Redistribution Mechanisms

Timpel, Melanie; Li, Hong; Nardi, Marco Vittorio; Wegner, Berthold; Frisch, Johannes; Hotchkiss, Peter J.; Marder, Seth R.; Barlow, Stephen; Brédas, Jean‐Luc; Koch, Norbert

doi:10.1002/adfm.201704438

Cited by 27 publications

(28 citation statements)

References 40 publications

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“…2b, these features are also clearly detected for F 6 TCNNQ on MoS 2 /HOPG, with essentially the same A/B intensity ratio. According to previous reports, these states can be assigned to anionic F 6 TCNNQ (F 6 TCNNQ −1 ), resulting from electron transfer to the molecules 39,40 . This assignment is further confirmed by density functional theory (DFT) calculations as provided in the Supplementary Note 1.…”

Section: Impact Of Ct On Work Function and Valence Electronic Levelsmentioning

confidence: 86%

Demonstration of the key substrate-dependent charge transfer mechanisms between monolayer MoS2 and molecular dopants

Park

Schultz

et al. 2019

Commun Phys

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Tuning the Fermi level (E F ) in two-dimensional transition metal dichalcogenide (TMDC) semiconductors is crucial for optimizing their application in (opto-)electronic devices. Doping by molecular electron acceptors and donors has been suggested as a promising method to achieve E F -adjustment. Here, we demonstrate that the charge transfer (CT) mechanism between TMDC and molecular dopant depends critically on the electrical nature of the substrate as well as its electronic coupling with the TMDC. Using angle-resolved ultraviolet and X-ray photoelectron spectroscopy, we reveal three fundamentally different, substratedependent CT mechanisms between the molecular electron acceptor 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane (F 6 TCNNQ) and a MoS 2 monolayer. Our results demonstrate that any substrate that acts as charge reservoir for dopant molecules can prohibit factual doping of a TMDC monolayer. On the other hand, the three different CT mechanisms can be exploited for the design of advanced heterostructures, exhibiting tailored electronic properties in (opto-)electronic devices based on two-dimensional semiconductors.

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Section: Impact Of Ct On Work Function and Valence Electronic Levelsmentioning

confidence: 86%

Demonstration of the key substrate-dependent charge transfer mechanisms between monolayer MoS2 and molecular dopants

Park

Schultz

et al. 2019

Commun Phys

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“…Currently, the enhancement of work function (WF) is the most critical issue for the development of AILs . Many research results indicated that WFs have significant influence on the open‐circuit voltage ( V oc ) of the devices . For instance, Vasilopoulou et al enhanced the WF of molybdenum oxide AILs from 5.4 to 5.9 eV by controlling the hydrogenation degree of Mo element, by which the V oc of the device increased from 0.59 to 0.65 V .…”

Section: Methodsmentioning

confidence: 99%

Significant Effect of Fluorination on Simultaneously Improving Work Function and Transparency of Anode Interlayer for Organic Solar Cells

Lü

Liao

et al. 2019

Advanced Energy Materials

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cathode interlayer materials that are successfully used in the efficient OSCs, anode interlayer (AIL) materials with satisfactory performances are rather rare. [15][16][17] Although several materials such as poly (3,4-ethylenedioxythiophene):(styrene sulfonate) (PEDOT:PSS) and metal oxides have been widely used as AILs, the acidic nature of PEDOT:PSS and the energy-consuming preparation process of metal oxides limit their practical uses in OSCs. [18][19][20][21] At present, the lack of ideal AILs has seriously impeded the pace toward practical application of OSCs.Currently, the enhancement of work function (WF) is the most critical issue for the development of AILs. [22,23] Many research results indicated that WFs have significant influence on the open-circuit voltage (V oc ) of the devices. [24,25] For instance, Vasilopoulou et al. enhanced the WF of molybdenum oxide AILs from 5.4 to 5.9 eV by controlling the hydrogenation degree of Mo element, by which the V oc of the device increased from 0.59 to 0.65 V. [26] Moreover, Irwin et al. prepared a NiO x AIL with a high WF of 5.4 eV, and achieved a V oc increment of 14 mV for the device. [27] However, in recent years, with the situation that the highest occupied molecular orbital (HOMO) levels of donors in fullerenefree devices are constantly downshifted for achieving high V oc , [28,29] most previously developed AILs cannot satisfy the new demands for modifying efficient OSCs because the low WFs of these materials give rise to large energy offsets with donors, which causes interfacial barrier for hole collection and leads to serious V oc loss. [30] Thus, it is particularly urgent to explore new approaches that can further enhance the WF of AILs.Among various materials, conjugated polyelectrolytes (CPEs) are promising candidates as AIL materials due to their neutral pH, excellent charge transporting capacity, and good filmforming property. [31,32] Unlike PEDOT:PSS and metal oxides, the chemical structure of CPEs can be readily modified through synthetic chemistry, which provides great opportunities for improving the WF of AILs. For example, Lee et al. enhanced the WF of p-PFP-X from 4.97 to 5.26 eV by tuning electric dipoles of the cation-anion pairs on the side chains of CPEs, and obtained an increased PCE of 9.2% in the OSC device. [33] However, these methods merely achieved limited WF enhancement and most of the developed AILs only worked well in fullerene-based OSCs. [34] Moreover, protonic acid doping has Since the highest occupied molecular orbital (HOMO) level of donors in organic solar cells (OSCs) is being constantly downshifted for achieving high open-circuit voltage (V oc ), a further enhancement of the anode work function (WF) is required. Herein, an effective approach of fluorinationis demonstrated to simultaneously improve the WF and transparency for anode interlayer (AIL) material. By fluorination, in combination with the dialysis treatment in LiCl solution, the WF of PCP-2F-Li could be significantly enhanced from 4.86 to 5.0 eV, as compared to PCP-Na...

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“…To determine the best simulation approach for investigating the surface properties of the ITO, our focus is on the comparison of the theoretical and experimental data. The main structural properties of the ITO that has been studied theoretically so far are optoelectronic properties such as band gap, work function, and charge injection rate [ 21 , 22 , 23 , 51 , 52 , 53 , 54 ]. Moreover, the time and size of the computational works are two main factors affecting the cost of the simulation.…”

Section: Computational Methods To Study the Surface Properties Of The Itomentioning

confidence: 99%

“…The surface modification of the ITO can also be investigated using first-principle calculations based on DFT [ 52 , 54 , 64 , 65 , 66 ]. Structural, optical, and electronic properties such as binding energy, band gap, work function, electronic coupling are the main properties that are calculated using DFT.…”

Section: Computational Methods To Study the Surface Properties Of The Itomentioning

confidence: 99%

“…In each mechanism, the orientation of the modifier and subsequently the net surface dipole at the interface changes. As such, the surface work function is changed [ 54 , 91 , 109 , 130 ]. For ITO thin films, several parameters in surface morphology such as dipole moment, active surface sites, geometry, and grain boundaries affect the electrical and optical properties of the film.…”

Section: Effects Of Surface Modification On the Structural Properties Of Itomentioning

confidence: 99%

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The Impact of the Surface Modification on Tin-Doped Indium Oxide Nanocomposite Properties

et al. 2022

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This review provides an analysis of the theoretical methods to study the effects of surface modification on structural properties of nanostructured indium tin oxide (ITO), mainly by organic compounds. The computational data are compared with experimental data such as X-ray diffraction (XRD), atomic force microscopy (AFM) and energy-dispersive X-ray spectroscopy (EDS) data with the focus on optoelectronic and electrocatalytic properties of the surface to investigate potential relations of these properties and applications of ITO in fields such as biosensing and electronic device fabrication. Our analysis shows that the change in optoelectronic properties of the surface is mainly due to functionalizing the surface with organic molecules and that the electrocatalytic properties vary as a function of size.

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Electrode Work Function Engineering with Phosphonic Acid Monolayers and Molecular Acceptors: Charge Redistribution Mechanisms

Cited by 27 publications

References 40 publications

Demonstration of the key substrate-dependent charge transfer mechanisms between monolayer MoS2 and molecular dopants

Demonstration of the key substrate-dependent charge transfer mechanisms between monolayer MoS2 and molecular dopants

Significant Effect of Fluorination on Simultaneously Improving Work Function and Transparency of Anode Interlayer for Organic Solar Cells

The Impact of the Surface Modification on Tin-Doped Indium Oxide Nanocomposite Properties

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