Spatially Correlated Charge Transport in Organic Thin Film Transistors

Dinelli, Franco; Murgia, Mauro; Lévy, P.; Cavallini, Massimiliano; Biscarini, Fabio; Leeuw, Dago M. de

doi:10.1103/physrevlett.92.116802

Cited by 602 publications

(535 citation statements)

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“…As also other important factors in organic electronic devices, e.g., photoluminescence or charge-carrier mobility 17, 43, 44 , depend on the orientation of the (intrinsically anisotropic) molecules, our approach of pre-patterning a metal surface with appropriate molecular species (shown here for DH6T) seems to be a promising tool for controlling the orientation of subsequently deposited molecules; for 6T, the gradual transition 31, 33 from lying to standing orientation can be reduced from hundreds of layers to only two.…”

Section: S Duhm Et Al Nature Materials Acceptedmentioning

confidence: 99%

“…For the occupied manifold of states discussed in the present study, this is the hole injection barrier (HIB) 6, 24 . While control over its orientation already allows considerably reducing the HIB into one and the same molecule by several tenths of an eV, the strategies for chemical modification suggested above can be expected to contribute to a further lowering; similar considerations hold for the unoccupied manifold of states connected to the electron injection barrier in n-type OFETs 23 .As also other important factors in organic electronic devices, e.g., photoluminescence or charge-carrier mobility 17, 43, 44 , depend on the orientation of the (intrinsically anisotropic) molecules, our approach of pre-patterning a metal surface with appropriate molecular species (shown here for DH6T) seems to be a promising tool for controlling the orientation of subsequently deposited molecules; for 6T, the gradual transition 31, 33 from lying to standing orientation can be reduced from hundreds of layers to only two. …”

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confidence: 99%

“…Since 6T and DH6T are used in organic field-effect transistors (OFETs) [17][18][19][20][21][22][23] , we discuss the immediate practical relevance of our findings in terms of the hole-injection barrier (HIB), a crucial parameter in organic electronic devices 6,24,25 . Pre-patterning an electrode with films of lying or standing DH6T allows for subsequent growth of films of likewise lying or standing 6T molecules and thus permits lowering the HIB at the Ag/6T contact by 0.4 eV.…”

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Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies

et al. 2008

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S. Duhm et al., Nature Materials, acceptedWhile an isolated individual molecule clearly has only one ionization potential, multiple values are found for molecules in ordered assemblies. Photoelectron spectroscopy of archetypical π-conjugated organic compounds on metal substrates combined with first-principles calculations and electrostatic modeling reveal the existence of a surface dipole built into molecular layers. Conceptually different from the surface dipole at metal surfaces, its origin lies in details of the molecular electronic structure and its magnitude depends on the orientation of molecules relative to the surface of an ordered assembly. Suitable pre-patterning of substrates to induce specific molecular orientations in subsequently grown films thus permits adjusting the ionization potential of one molecular species over up to 0.6 eV via control over monolayer morphology. In addition to providing in-depth understanding of this phenomenon, our study offers design guidelines for improved organic/organic heterojunctions, hole-or electron-blocking layers, and reduced barriers for charge-carrier injection in organic electronic devices. S. Duhm et al., Nature Materials, acceptedIt is well established that the work function (Φ) of metals depends on the crystal face 1-3 .Φ is defined as the energy difference between the Fermi level (E F ) and the electrostatic potential above the sample, the vacuum level (V vac ). For, e.g., copper, Φs of the (100), (110), and (111) surfaces are spread over a range of 0.5 eV 1,2 . As E F is constant, this observation has been explained by the difference in the intrinsic "surface dipole": Differences in the geometric and, consequently, electronic structure cause a different amount of the electronic cloud to spill out of the bulk into the vacuum 3, 4 . The resulting dipole raises V vac to a larger or smaller extent and thus impacts Φ 4, 5 . Note that this effect can only be observed for laterally extended surfaces, as the spatial region above the sample where V vac is raised reaches farther away from the surface with increasing sample size (i.e., area of the exposed surface) 6, 7 . Small metal clusters with multiple facets of different crystal orientations have only one well-defined work function 8, 9 .For van der Waals (i.e., non-covalent) crystals of non-dipolar molecules, surface dipoles and work-function anisotropy have not yet been explored 6 . While variations of the ionization potential (IP; the molecular equivalent of the work function) depending on the molecular orientation on a substrate have been reported before [10][11][12][13][14][15][16] , the prevalent interpretation in terms of variable photo-hole screening could never be satisfactorily quantified. Here, we propose a qualitatively different and novel explanation for the intriguing observation that one and the same molecule can have different -still welldefined -IPs if part of an ordered supramolecular structure. S. Duhm et al., Nature Materials, acceptedWe performed X-ray photoelectron spectroscopy (XPS) and u...

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Section: S Duhm Et Al Nature Materials Acceptedmentioning

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Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies

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“…[1][2][3][4][5] The sub-nm scale is the typical distance of intermolecular and -stacking interactions, which determine the hopping rate of charge carriers and polarization effects; the 1-10 nm scale is the effective Debye length of the organic semiconductor that corresponds to the thickness of the accumulation layer; the longitudinal electrostatic potential drops across charge injection interfaces and domain boundaries on the 10 nm scale; the 100-1000 nm is the lateral length scale of semiconductor domains; tens of micrometers is the channel length where charge carriers move.…”

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confidence: 99%

Changes of the Molecular Structure in Organic Thin Film Transistors during Operation

et al. 2015

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Thin films of organic semiconductors have been widely studied at different length scales for improving the electrical response of devices based on them. Hitherto, a lot of knowledge has been gained about how molecular packing, morphology, grain boundaries, and defects affect the charge transport in organic thin film transistors. However, little is known about the impact of an electric field on the organic semiconductor microstructure and the consequent effect on the device performances. To fill this gap, we investigated the evolution of the structure of pentacene thin film transistors during device operation by in situ real time X-ray diffraction measurements and theoretical calculations. We observed for the first time the occurrence of a reversible structural strain taking place during the bias application mainly due to reorientation at the terrace edges of monolayer islands under the effect of electrical field. Strain exhibits the same trend of the threshold voltage hinting to the existence of a direct correlation between the phenomenon of bias stress and the structural modification.2

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“…[10][11][12][13][14][15] Moreover, downscaling the film thickness to a single molecular layer is of technological interest for the realization of bottomup electronic devices. [16][17][18] In particular, monolayer organic FETs (OFETs) are beneficial for sensing applications as the binding of the respective analytes with the semiconducting monolayer is expected to affect the charge transporting.…”

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Diketopyrrolopyrrole‐Based Semiconducting Polymer with Both Hydrophobic Alkyl and Hydrophilic Tetraethylene Glycol Chains for Monolayer Transistor and Sensing Application

Yang

Zhang

Chen

et al. 2017

Adv Elect Materials

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studies also suggest that the first few layers of organic/polymeric semiconductors play key roles in determining the performances of FETs. [10][11][12][13][14][15] Moreover, downscaling the film thickness to a single molecular layer is of technological interest for the realization of bottomup electronic devices. [16][17][18] In particular, monolayer organic FETs (OFETs) are beneficial for sensing applications as the binding of the respective analytes with the semiconducting monolayer is expected to affect the charge transporting. [19][20][21][22][23] Consequently, such sensors with monolayer FETs can show high sensitivity and fast response.Various approaches have been explored to fabricate FETs with ultrathin semiconducting films. These include unconventional spin-coating and formation of self-assembly monolayer on surface. [24][25][26][27][28] Langmuir deposition method is known to enable the realization of monolayers at the air/liquid interface with precision control over the molecule lateral packing density. In fact, Langmuir technique was successfully utilized to transfer monolayer thin films of organic and polymeric semiconductors onto the substrates to fabricate FETs. [29][30][31][32][33][34][35] For instance, Yli-Lahti and co-workers first reported FETs with Langmuir-Blodgett (LB) films of poly(3-hexylthicphene)/ arachidic acid, but the resulting FETs exhibited rather low charge mobilities. [34] This is probably due to the fact that the LB films contain arachidic acid which is required for the formation of the polymer LB films at air-water interface. Facchetti and Pignataro and co-workers prepared n-type monolayer FET with naphthalene diimide based polymer (P (NDI2OD-T2)) by using Langmuir-Schaefer method. [35] These conjugated polymers are basically hydrophobic, but it is known that amphiphilic molecules with both hydrophobic and hydrophilic moieties can form more ordered monolayers at the air-water interface. [36][37][38] Leclerc and co-workers studied the formation of LB monolayers at air-water interface and the transfer of the monolayers onto the substrate for the conjugated polymer with both alkyl and oligo(ethylene glycol) side chains, but the semiconducting properties of the monolayers were not addressed. [38] Functional field-effect transistors (FETs) have received increasing attention in recent years. Herein, it is demonstrated that the incorporation of hydrophilic tetraethylene glycol (TEEG) chains into the diketopyrrolopyrrole (DPP)-based semiconducting polymer (PDPP3T1) can facilitate the formation of polymeric monolayer at the air-water interface, and the resulting field-effect transistors (FETs) show sensitive and selective response toward alcohol vapor. By using the Langmuir-Schaefer method, monolayer and ultrathin films from bilayer to five-layer can be successfully prepared. Interestingly, nanopores with sizes of 50-100 nm are formed within the monolayer film, as observed by using atomic force microscopy. The monolayer FET exhibits relatively high hole mobilities up to 0.014 cm 2 V −1 s −...

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Spatially Correlated Charge Transport in Organic Thin Film Transistors

Cited by 602 publications

References 26 publications

Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies

Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies

Changes of the Molecular Structure in Organic Thin Film Transistors during Operation

Diketopyrrolopyrrole‐Based Semiconducting Polymer with Both Hydrophobic Alkyl and Hydrophilic Tetraethylene Glycol Chains for Monolayer Transistor and Sensing Application

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