Transition from trap-controlled to trap-to-trap hopping transport in disordered organic semiconductors

Fishchuk, I. I.; Kadashchuk, A.; Vakhnin, A.; Korosko, Yu.; Bäßler, H.; Souharce, Benjamin; Scherf, Ulrich

doi:10.1103/physrevb.73.115210

Cited by 61 publications

(53 citation statements)

References 38 publications

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“…Thus, the extrapolation of the Arrhenius ln͑͒ ϰ T −1 dependence of the mobility to infinite temperature is at clear variance with the concept of charge hopping transport in organic random systems with a Gaussian-type DOS, that has been also recently discussed by van Mensfoort et al, 33 even though the conventional experimentally accessible temperature range does not allow experimental verification of the predicted change to ϳT −2 dependence at a higher temperature. This effect is expected to be also held for a more complex DOS profiles, e.g., a bimodal Gaussian DOS distribution relevant to trap containing materials, 39,40 as this does not change the basic Gaussian disorder formalism.…”

Section: Discussionmentioning

confidence: 99%

Temperature dependence of the charge carrier mobility in disordered organic semiconductors at large carrier concentrations

et al. 2010

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Temperature-activated charge transport in disordered organic semiconductors at large carrier concentrations, especially relevant in organic field-effect transistors ͑OFETs͒, has been thoroughly considered using a recently developed analytical formalism assuming a Gaussian density-of-states ͑DOS͒ distribution and MillerAbrahams jump rates. We demonstrate that the apparent Meyer-Neldel compensation rule ͑MNR͒ is recovered regarding the temperature dependences of the charge carrier mobility upon varying the carrier concentration but not regarding varying the width of the DOS. We show that establishment of the MNR is a characteristic signature of hopping transport in a random system with variable carrier concentration. The polaron formation was not involved to rationalize this phenomenon. The MNR effect has been studied in a OFET based on C 60 films, a material with negligible electron-phonon coupling, and successfully described by the present model. We show that this phenomenon is entirely due to the evolution of the occupational DOS profile upon increasing carrier concentration and this mechanism is specific to materials with Gaussian-shaped DOS. The suggested model provides compact analytical relations which can be readily used for the evaluation of important material parameters from experimentally accessible data on temperature dependence of the mobility in organic electronic devices. Experimental results on temperature-dependent charge mobility reported before for organic semiconductors by other authors can be well interpreted by using the model presented in this paper. In addition, the presented analytical formalism predicts a transition to a Mott-type charge carrier hopping regime at very low temperatures, which also manifests a MNR effect.

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Section: Discussionmentioning

confidence: 99%

Temperature dependence of the charge carrier mobility in disordered organic semiconductors at large carrier concentrations

et al. 2010

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“…II. We have developed a model for treating the mobility in the HGH-GG transition region that goes beyond the approach presented by Fishchuk et al, 14 in two respects: ͑i͒ the carrier concentration dependence of the effect is taken into account, and ͑ii͒ the possibility that the wave function extensions of the host and guest molecules are different is included. In Sec.…”

Section: ͑2͒mentioning

confidence: 99%

“…extended their model in order to include the transition around x = x min between the HGH and GG hopping regimes. 14 In spite of this progress, the theoretical models developed so far still lack an important ingredient: the mobility does not only depend on the guest concentration, but also on the charge carrier concentration, c. It is the purpose of this paper to demonstrate the relevance of this effect, by showing the results from a model for the dependence of the mobility on x and c, for the case of a bimodal Gaussian DOS. We discuss the relevance of this effect for OLEDs, and argue that it might provide an explanation for an unresolved discrepancy between the ͑x͒ curves observed from time-of-flight ͑TOF͒ experiments for certain well-characterized amine-based hostguest systems and the so far available models.…”

Section: Introductionmentioning

confidence: 96%

Hopping mobility of charge carriers in disordered organic host-guest systems: Dependence on the charge-carrier concentration

Coehoorn

2007

Phys. Rev. B

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Citation for published version (APA): Coehoorn, R. (2007). Hopping mobility of charge carriers in disordered organic host-guest systems: Dependence on the charge-carrier concentration. Physical Review B, 75(15) Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: openaccess@tue.nl providing details and we will investigate your claim. The hopping mobility of charge carriers in disordered organic host-guest systems with a bimodal Gaussian density of states is studied. Two semianalytical models are used, viz. a relatively simple Mott-type model and a more advanced but computationally less efficient effective medium model. The latter model has been generalized, in order to be able to include the effect of different wave function extensions of the host and guest molecules. It is shown that energetic disorder can result in a pronounced charge carrier concentration dependence of the mobility. This provides an explanation so far for unresolved issues concerning the guest concentration dependence of the measured hole mobility in some well-characterized host-guest systems. It is also argued that treating the mobility as a carrier concentration dependent quantity is highly relevant to the modeling of carrier transport in organic light emitting devices ͑OLEDs͒, consisting of an organic matrix material with embedded fluorescent or phosphorescent dye molecules.

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“…This "field-induced detrapping" ͑FID͒ effect gives rise to an additional contribution to the mobility. So far, this effect has only been studied for specific host-guest systems using various semianalytical approximations [20][21][22][23][24][25][26] and a general model for the effect that may be readily used in driftdiffusion device simulations of organic electronic devices is lacking.…”

Section: Introductionmentioning

confidence: 99%

Field-induced detrapping in disordered organic semiconducting host-guest systems

2010

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In a disordered organic semiconducting host-guest material, containing a relatively small concentration of guest molecules acting as traps, the charge transport may be viewed as resulting from carriers that are detrapped from the guest to the host. Commonly used theories include only detrapping due to thermal excitation, described by the Fermi-Dirac ͑FD͒ distribution function. In this paper, we develop a theory describing the effect of field-induced detrapping ͑FID͒, which provides an additional contribution at finite electric fields. It is found from three-dimensional simulations that the FID effect can be described by a field-dependent generalized FD distribution that depends only on the shape of the host density of states ͑DOS͒ and not on the guest DOS. For the specific case of a Gaussian host DOS, we give an accurate and easy-to-use analytical expression for this distribution. The application of our theory is demonstrated for sandwich-type devices under conditions typical of organic light-emitting diodes.

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Transition from trap-controlled to trap-to-trap hopping transport in disordered organic semiconductors

Cited by 61 publications

References 38 publications

Temperature dependence of the charge carrier mobility in disordered organic semiconductors at large carrier concentrations

Temperature dependence of the charge carrier mobility in disordered organic semiconductors at large carrier concentrations

Hopping mobility of charge carriers in disordered organic host-guest systems: Dependence on the charge-carrier concentration

Field-induced detrapping in disordered organic semiconducting host-guest systems

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