Organometallic Dimers: Application to Work-Function Reduction of Conducting Oxides

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Doping of graphene is a viable route towards enhancing its electrical conductivity and modulating its work function for a wide range of technological applications. In this work, we demonstrate facile, solution-based, non-covalent surface doping of few-layer graphene (FLG) using a series of molecular metal-organic and organic species of varying n-and p-type doping strengths. In doing so we tune the electronic, optical and transport properties of FLG. We modulate the work function of graphene over a range of 2.4 eV (from 2.9 to 5.3 eV) -unprecedented for solution-based doping -via surface electron transfer. A substantial improvement of the conductivity of FLG is attributed to increasing carrier density, slightly offset by a minor reduction of mobility via Coulomb scattering. The mobility of single layer graphene has been reported to decrease significantly more via similar surface doping than FLG, which has the ability to screen buried layers. The dopant dosage influences the properties of FLG and reveals an optimal window of dopant coverage for the best transport 2 properties, wherein dopant molecules aggregate into small and isolated clusters on the surface of FLG. This study shows how soluble molecular dopants can easily and effectively tune the work function and improve the optoelectronic properties of graphene.

Section: Ev)mentioning

confidence: 81%

Facile Doping and Work‐Function Modification of Few‐Layer Graphene Using Molecular Oxidants and Reductants

Mansour

Said

Dey

et al. 2017

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“…[ 37 ] We also confi rmed that the low-WF character remains even after air exposure, which is consistent with the previous results. [ 20 ] The resulting WF for the air-exposed (up to 24 h) electrodes is still lower than 4 eV, which is comparable to prototypical cathode buffer-layers such as titanium dioxide that are frequently used in OPV cells. [ 38 ] Notably, the drop-cast modifi ed electrodes were found to be more air stable than their vacuum-deposited counterparts.…”

Section: Discussionmentioning

confidence: 95%

“…In the present case, the interfacial electron transfer converts the neutral 1 2 to the cationic monomers of 1 2 ( 1 + ). [ 11,19,20 ] The positive potential caused by the resulting surface layer of 1 + cations leads to the WF reduction of the substrates.…”

Section: Work Function Reduction By Evaporationmentioning

confidence: 99%

“…The WF increase can be attributed to the reduction of H 2 O/ O 2 by (excess) neutral 1 2 and/or by the electrons transferred initially to substrate. [ 20 ] As a result, possible reaction products from the ambient gases, most likely OHand O 2 -, may be generated and weaken the initial interface dipoles with the negative charges at the substrate side. The enhanced O 1s peak after the air exposure supports this mechanism ( Figure S3, Supporting Information).…”

Section: Impact Of Air Exposure On 1 2 -Covered Electrodesmentioning

confidence: 99%

“…[ 17,18 ] The dimers formed by some 19-electron organometallic sandwich compounds, such as the dimer of 1,2,3,4,5-pentamethylrhodocene ( 1 2 , molecular structure shown in Figure 1 ), are promising candidates for this purpose: their reductant ability has already been demonstrated by the effective n-doping for a variety of organic semiconductors, [ 19 ] their 18-electron confi gurations lead to moderate air stability, and they can be processed using both vacuum deposition at low temperature (≈120 °C) and solution processes. [ 19 ] Indeed, the Ir analogue of 1 2 has been used to reduce the WF of indium tin oxide (ITO), ZnO, and Au via dip coating, [ 20 ] the dimer of ruthenium pentamethylcyclopentadienyl mesitylene has been shown to reduce the WF of ITO by dip coating [ 20 ] and that of ZnO through vacuum processing, [ 21 ] and 1 2 has been used to reduce the WF of chemical-vapor-deposition (CVD) graphene by dip coating. [ 11 ] However, the general applicability of this approach to other device-relevant electrode materials has not been investigated.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Effective Work Function Reduction of Practical Electrodes Using an Organometallic Dimer

Akaike

Nardi

Oehzelt

et al. 2016

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The control of the cathode work function (WF) is essential to enable efficient electron injection and extraction at organic semiconductor/cathode interfaces in organic electronic devices. The adsorption of an air-stable molecular donor onto electrodes, compatible with both evaporation and solution processes, is a simple way to reduce the WF. Such a versatile molecule, however, has not been identified yet. In this paper, ultraviolet photoelectron spectroscopy is used to confirm that depositing an ultrathin layer of the moderately air-stable pentamethylrhodocene-dimer onto various conducting electrodes, by either vacuum 2 deposition or drop-casting from solution, substantially reduces their WF to less than 3.6 eV, with 2.8 eV being the lowest attainable value. Detailed measurements of the Rh core levels with X-ray photoelectron spectroscopy reveal that the electron transfer from the molecule to the respective substrates is responsible for the appreciable WF reduction. Notably, even after air-exposure, the WF of the donor-covered electrodes remains below those of typically used clean cathode-metals such as Al and Ag, rendering the approach appealing for practical applications. The WF reduction, together with the observed air-stability of the covered electrodes, demonstrates the applicability of the pentamethylrhodocene-dimer to reduce the WF for a wide range of electrodes used in all-organic or organic-inorganic hybrid devices.

The Interlayer Method: A Universal Tool for Energy Level Alignment Tuning at Inorganic/Organic Semiconductor Heterojunctions

Schultz

Lungwitz

Longhi

et al. 2020

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The combination of inorganic and organic semiconductors in a heterojunction is considered a promising approach to overcome limitations of each individual material class. However, to date only few examples of improved (opto‐)electronic functionality have been realized with such hybrid heterojunctions. The key to unraveling the full potential offered by inorganic/organic semiconductor heterojunctions is the ability to deliberately control the interfacial electronic energy levels. Here, a universal approach to adjust the offset between the energy levels at inorganic/organic semiconductor interfaces is demonstrated: the interlayer method. A monolayer‐thick interlayer comprising strong electron donor or acceptor molecules is inserted between the two semiconductors and alters the energy level alignment due to charge transfer with the inorganic semiconductor. The general applicability of this method by tuning the energy levels of hydrogenated silicon relative to those of vacuum‐processed films of a molecular semiconductor as well as solution‐processed films of a polymer semiconductor is exemplified, and is shown that the energy level offset can be changed by up to 1.8 eV. This approach can be used to adjust the energy levels at the junction of a desired material pair at will, and thus paves the way for novel functionalities of optoelectronic devices.