Bipolar transport in organic field-effect transistors: organic semiconductor blends versus contact modification

Opitz, Andreas; Kraus, Michael; Bronner, Markus; Wagner, Johannes; Brütting, Wolfgang

doi:10.1088/1367-2630/10/6/065006

Cited by 17 publications

(17 citation statements)

References 30 publications

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“…11) is higher than the sum of the unipolar hole and electron mobilities. This should be related to the ambipolar nature of both materials 20. Nevertheless the transport in the blended films is based mainly on the transport of electrons by the C 60 molecules.…”

Section: Resultsmentioning

confidence: 99%

“…3) was used. As seen in measurements of field‐effect transistors, the F 4 TCNQ layer improves the hole injection 22 and therefore an F 4 TCNQ/Au contact is non‐injecting for electrons 20. The electron‐only diodes contain a 30 nm thick Al electrode at the bottom and a 30 nm thick Al electrode on top of the organic film with a 0.5 nm thick interface doping layer of LiF.…”

Section: Materials Devices and Experimental Methodsmentioning

confidence: 98%

“…In both cases, balanced hole and electron mobilities were achieved for certain concentration ratios, giving the best performance of inverters or light‐emitting OFETs. Ambipolar transport was also found in neat materials 18–20; however, there the mobilities cannot be tuned. So mixing of electron and hole transporting materials has the advantage to adjust balanced mobilities by the concentration ratio which is impossible for neat materials.…”

Section: Introductionmentioning

confidence: 96%

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Molecular semiconductor blends: Microstructure, charge carrier transport, and application in photovoltaic cells

Opitz

Wagner

Brütting

et al. 2009

Physica Status Solidi (a)

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Ambipolar organic semiconductor blends, i.e. mixtures of electron and hole conducting materials, attain growing interest due to their utilization in quasi‐complementary organic field‐effect transistors and organic photovoltaic cells. Many investigations in the latter field have reported an increase of the solar cell efficiency by optimizing the balance between charge carrier transport in phase‐separated structures and exciton dissociation at the interface between these phases. Here we show the implications of blending molecular materials for structural, optical, and electrical properties in two model systems for organic photovoltaic cells. We have investigated blends and neat films of the hole transporting material Cu‐phthalocyanine (CuPc) together with fullerene C60 and Cu‐hexadecafluorophthalocyanine (F16CuPc) as electron transporting materials, respectively. On the one hand, the difference in molecular structure of the spherical C60 and the planar molecule CuPc leads to nanophase separation in a blend of both of them, causing charge carrier transport being limited by the successful formation of percolation paths. On the other hand, blends of the similar shaped CuPc and F16CuPc molecules entail mixed crystalline films, as can be clearly seen by X‐ray scattering measurements. We discuss differences of both systems with respect to their microstructure as well as their electrical transport properties in diodes and field‐effect transistors. Furthermore, we compare the photovoltaic properties of planar‐ and bulk‐heterojunction devices under white light illumination to relate the different morphologies of both material systems to their performance in solar cells. Sketches of different molecular arrangements in blended systems. The formation of phase‐separated (left) or molecularly mixed crystalline films (right) can occur, depending on the geometry of the involved molecules.

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Section: Resultsmentioning

confidence: 99%

Section: Materials Devices and Experimental Methodsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 96%

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Molecular semiconductor blends: Microstructure, charge carrier transport, and application in photovoltaic cells

Opitz

Wagner

Brütting

et al. 2009

Physica Status Solidi (a)

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“…Regarding the experimental realization of the ferromagnetic and the half-metallic states derived above, we note that the required electron doping of the pentagon chains can, in principle, be achieved [20] by two means: first by raising the Fermi level by selecting appropriate side groups, and second by field-effect doping in a double-layer transistor structure [21]. Specifically for polythiophene with an estimated density of 10 14 pentagon rings=cm 2 [22], electron densities of the order 10 15 -10 16 carriers=cm 2 are required.…”

Section: -2mentioning

confidence: 99%

Route to Ferromagnetism in Organic Polymers

2010

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Employing a rigorous theoretical method for the construction of exact many-electron ground states we prove that interactions can be employed to tune a bare dispersive band structure such that it develops a flat band. Thereby, we show that pentagon-chain polymers with electron densities above half filling may be designed to become ferromagnetic or half metallic. [7][8][9] was studied in the search for plastic ferromagnets and, more generally, for ferromagnetism in systems made entirely of nonmagnetic elements. The possibility for ferromagnetism in these systems was investigated theoretically [10,11], with a particular focus on ferromagnetism due to flat electronic bands arising in odd-membered ring structures [12]. Particular attention was paid to the role of side groups of the pentagon ring, since these may cause flat bands in the band structure. Suwa et al. [13] proposed that ferromagnetism in pentagon-chain polymers such as polydimethylaminopyrrole is related to the hybridization of narrow bands with wide bands and therefore modeled this polymer by a periodic Anderson model. In the latter model the electronic interaction acts site selective within the unit cell and the choice of this model [13] was an attempt to account for the different atoms on the pentagon chain.In this Letter we investigate pentagon-chain polymers (see Fig. 1) by a general multiband Hubbard model where the electrons experience local Coulomb interactions on all lattice sites. The microscopic parameters are chosen such that they account for the particular environment and type of atom in the unit cell of the material; in particular, in our approach repulsive on-site interactions are permitted to differ on individual sites. Similarly, we also include bond dependent hopping amplitudes. The hopping parameters are not assumed to take special values leading to flat bands in the bare band structure. By contrast we will show rigorously that the dispersion of the correlated system may be tuned by the interaction to become flat. Thereby transitions to ferromagnetic states or correlated halfmetallic states at high electron densities may be induced. We thus prove by exact means the conjecture of Brocks et al. [14] that the Coulomb interaction is able to stabilize magnetic order in acene and thiophene.Our analytic approach proceeds in three steps: the transformation of the Hamiltonian into positive semidefinite form, the construction of ground states, and the proof of their uniqueness. This technique is independent of the spatial dimension and does not require integrability of the model. Previously it was successfully applied to construct exact ground states for Hubbard chains with other geometrical structures [15] and even for the threedimensional periodic Anderson model [16]. Details of the method are described in Ref. [15].Since the analytic technique employed here is applicable to a large class of chains we discuss it in its general form, and then specify it to a model analysis of the organic pentagon chain shown in Fig. 1. The unit cell contains m ...

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“…10͒ and 2.7 eV, 18 respectively, resulting in a lowest unoccupied molecular orbital ͑LUMO͒ of 2.65 eV. As reported, e.g., for copper phthalocyanine, 19 the injection of electrons from Al top contacts ͑for work function values see Table I͒ works very well. A clear asymmetry between the injection barriers from the Fermi level of Al to the HOMO and LUMO of DIP is expected, thus no holes are injected from Al electrodes.…”

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confidence: 58%

Diindenoperylene as ambipolar semiconductor: Influence of electrode materials and mobility asymmetry in organic field-effect transistors

Horlet

Kraus

Brütting

et al. 2011

Applied Physics Letters

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Organic field-effect transistors were prepared using diindenoperylene as molecular semiconductor. An insulating alkane layer was used to separate the semiconductor from the underlying oxide and to suppress effects of electron traps at that surface. Diindenoperylene transistors were studied for various electrode materials. Unipolar p-and n-type as well as ambipolar devices were realized. An electron mobility of up to 0.14 cm 2 / V s and a hole mobility of up to 0.052 cm 2 / V s were found. The temperature dependent analysis shows similar trap distributions for both carrier types. Therefore the asymmetry in electron and hole transport seems to be an intrinsic effect of diindenoperylene.

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Bipolar transport in organic field-effect transistors: organic semiconductor blends versus contact modification

Cited by 17 publications

References 30 publications

Molecular semiconductor blends: Microstructure, charge carrier transport, and application in photovoltaic cells

Molecular semiconductor blends: Microstructure, charge carrier transport, and application in photovoltaic cells

Route to Ferromagnetism in Organic Polymers

Diindenoperylene as ambipolar semiconductor: Influence of electrode materials and mobility asymmetry in organic field-effect transistors

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