Energy-level alignment at strongly coupled organic–metal interfaces

Chen, Meng Ting; Hofmann, Oliver; Gerlach, Alexander; Bröker, Benjamin; Bürker, Christoph; Niederhausen, Jens; Hosokai, Takuya; Zegenhagen, J.; Vollmer, Antje; Rieger, Ralph; Müllen, Kläus; Schreiber, Frank; Salzmann, Ingo; Koch, Norbert; Zojer, Egbert; Duhm, Steffen

doi:10.1088/1361-648x/ab0171

Cited by 15 publications

(23 citation statements)

References 132 publications

(146 reference statements)

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“…When molecules are physisorbed, they couple weakly to the metal surface and the alignment of energy levels can approach the Schottky–Mott limit, where φ B is controlled by the metal work function and the semiconductor HOMO/LUMO levels . For strong molecule–metal interactions, such as the case of chemisorbed molecules, charge transfer from the metal to the semiconductor molecules leads to the formation of large surface dipoles, making the band diagram of the isolated material surfaces irrelevant . The strength of the coupling between the organic semiconductor and the electrode can be tuned, to a certain extent, by processing.…”

Section: Charge Injection Through a Metal–semiconductor Interfacementioning

confidence: 99%

Contact Resistance in Organic Field‐Effect Transistors: Conquering the Barrier

Waldrip

Jurchescu

Gundlach

et al. 2019

Adv Funct Materials

226

261

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Organic semiconductors have sparked interest as flexible, solution processable, and chemically tunable electronic materials. Improvements in charge carrier mobility put organic semiconductors in a competitive position for incorporation in a variety of (opto-)electronic applications. One example is the organic field-effect transistor (OFET), which is the fundamental building block of many applications based on organic semiconductors. While the semiconductor performance improvements opened up the possibilities for applying organic materials as active components in fast switching electrical devices, the ability to make good electrical contact hinders further development of deployable electronics. Additionally, inefficient contacts represent serious bottlenecks in identifying new electronic materials by inhibiting access to their intrinsic properties or providing misleading information. Recent work focused on the relationships of contact resistance with device architecture, applied voltage, metal and dielectric interfaces, has led to a steady reduction in contact resistance in OFETs. While impressive progress was made, contact resistance is still above the limits necessary to drive devices at the speed required for many active electronic components. Here, the origins of contact resistance and recent improvement in organic transistors are presented, with emphasis on the electric field and geometric considerations of charge injection in OFETs.semiconductors with superior intrinsic charge transport properties, there is a stringent need to improve the device properties in order to allow organic devices to fulfill their technological prospectives. In the organic semiconductor community, contact resistance (R C ) has come under increased scrutiny as it is apparent that the final device performance is often domi nated by carrier injection, rather than the transport through the semiconductor layer. Contact resistance can impact OFET development in multiple ways. First, if not accounted for, a high contact resistance may lead to inaccurate extraction of the device parameters. Second, any inaccuracies in parameter extraction can have significant consequences on material development, from generating incorrect structure-property relationships to discarding organic semiconductors whose efficient intrinsic electrical properties have been masked by inefficient contacts. Beyond OFET and semiconductor characterization, analog, low power, and high frequency applications require a greater level of device parameter control than has been obtained in typical DC, high-voltage OFETs. For analog applications, e.g., integration of conditioning circuits such as local sense amps for distributed flexible sensor arrays, nonlinearity of the transistor response inhibits proper functioning and limits applicability of common models used to design circuitry. Low power device development for novel materials are hindered by the high voltage turn-on and current suppression in devices with large R C . Considering high-frequency applications, Klauk suggest...

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Section: Charge Injection Through a Metal–semiconductor Interfacementioning

confidence: 99%

Contact Resistance in Organic Field‐Effect Transistors: Conquering the Barrier

Waldrip

Jurchescu

Gundlach

et al. 2019

Adv Funct Materials

226

261

View full text Add to dashboard Cite

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“…There, for upright-standing molecular layers, work functions in excess of 6.1 eV have been measured. [272] A particularly interesting situation is encountered for 1,2,5,6,9,10-coronenehexone (COHON) on coinage metals (see Figure 15c): [271] While the work functions of the pristine substrates and at very low coverages of COHON on Au, Cu, and Ag are significantly different, at a nominal coverage of ≈6 Å (which is attributed to roughly a closed monolayer of lying molecules) the work functions of COHON/Ag and COHON/Cu become virtually identical. This suggests Fermi-level pinning at those two interfaces, while on Au pinning apparently does not occur yet and the electronic structure of the interface is dominated by Pauli pushback.…”

Section: Fermi-level Pinningmentioning

confidence: 99%

“…Interestingly, at least for the COHON/Cu interface there is indeed further spectroscopic evidence for such a coverage-dependent reorientation. [271] All these examples indicate that coverage-dependent rearrangements of organic molecules on metal surfaces have massive consequences for their electronic properties. At this stage we speculate that such rearrangements might occur much more often than usually assumed.…”

Section: Fermi-level Pinningmentioning

confidence: 99%

The Impact of Dipolar Layers on the Electronic Properties of Organic/Inorganic Hybrid Interfaces

Zojer

Taucher

Hofmann

2019

Adv Materials Inter

Self Cite

133

168

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The presence of dipolar layers determines the functionality of most technologically relevant interfaces. The present contribution reviews how periodic dipole assemblies modify the properties of such interfaces through so‐called collective electrostatic effects. They impact the ionization energies and electron affinities of thin films, change the work function of metallic and semiconducting substrates, and determine the alignment of electronic states at interfaces. Dipolar layers originate either from the assembly of polar molecules or they arise from interfacial charge rearrangements triggered by the deposition of an adsorbate layer. Such charge rearrangements result from the omnipresent Pauli pushback caused by exchange interaction, from covalent bonds, or from charge transfer following the deposition of particularly electron rich (donors) or electron poor molecules (acceptors). A peculiarity of charge‐transfer interfaces is that they enter the realm of Fermi‐level pinning, where the sample work function becomes independent of the substrate and is solely determined by the electronic properties of the adsorbate. Beyond changing work functions and injection barriers, the presence of polar layers also modifies various other physical observables, like core‐level binding energies or tunneling currents in monolayer junctions. All these aspects suggest that polar layers can also be exploited for electrostatically designing the electronic properties of materials.

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“…Such interfaces are typically formed by depositing the organic semiconductor on top of the clean metal substrate such as copper and silver. [ 107–110 ] A chemical bond will be formed if more bonding than antibonding hybrid orbitals is occupied. The fractional charge transfer can occur when the hybrid orbitals are highly polarized.…”

Section: Energy‐level Alignment At Electrode–organic Interfacementioning

confidence: 99%

Interface Engineering in Organic Electronics: Energy‐Level Alignment and Charge Transport

2020

Small Science

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Organic light‐emitting diodes (OLEDs) and organic solar cells are new members of trillion‐dollar semiconductor industry. The structure of these devices generally consists of a stack of several organic layers sandwiched between two electrodes. The electronic processes such as the energy‐level alignment at and charge transport across these interfaces play a key role to the overall performance of the organic devices. Thus, interface physics is important for design and engineering of organic devices. Herein, recent progress in energy‐level alignment at and charge transport across organic interfaces is reviewed. In addition, basic material physics of organic semiconductors such as energy levels, energy disorder, and molecular orientation is introduced. Recent progress in theories and experiments on energy‐level alignment at and charge transport across molecular heterojunctions is then discussed. Case studies of applying interface physics for guiding fabrication of ideal devices are also provided.

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Energy-level alignment at strongly coupled organic–metal interfaces

Cited by 15 publications

References 132 publications

Contact Resistance in Organic Field‐Effect Transistors: Conquering the Barrier

Contact Resistance in Organic Field‐Effect Transistors: Conquering the Barrier

The Impact of Dipolar Layers on the Electronic Properties of Organic/Inorganic Hybrid Interfaces

Interface Engineering in Organic Electronics: Energy‐Level Alignment and Charge Transport

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