Charge Carrier Motion in Disordered Conjugated Polymers: A Multiscale Ab Initio Study

Vukmirović, Nenad; Wang, Lin‐Wang

doi:10.1021/nl9021539

Cited by 86 publications

(122 citation statements)

References 35 publications

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“…17,18 This approach has been used to calculate mobility in columnar discotic mesophases, 19−24 amorphous systems, 25−28 selfassembled monoloayers, 29 and conjugated polymers. 30,31 An amorphous morphology of 4096 BTDF molecules is obtained by first annealing the system at 700 K, well above the glass transition temperature, T g = 380 K, followed by fast quenching to room temperature. The final length of the cubic box is L = 16 nm.…”

Section: Resultsmentioning

confidence: 99%

Design Rules for Charge-Transport Efficient Host Materials for Phosphorescent Organic Light-Emitting Diodes

et al. 2012

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The use of blue phosphorescent emitters in organic light-emitting diodes (OLEDs) imposes demanding requirements on a host material. Among these are large triplet energies, the alignment of levels with respect to the emitter, the ability to form and sustain amorphous order, material processability, and an adequate charge carrier mobility. A possible design strategy is to choose a π-conjugated core with a high triplet level and to fulfill the other requirements by using suitable substituents. Bulky substituents, however, induce large spatial separations between conjugated cores, can substantially reduce intermolecular electronic couplings, and decrease the charge mobility of the host. In this work we analyze charge transport in amorphous 2,8-bis(triphenylsilyl)dibenzofuran, an electron-transporting material synthesized to serve as a host in deep-blue OLEDs. We show that mesomeric effects delocalize the frontier orbitals over the substituents recovering strong electronic couplings and lowering reorganization energies, especially for electrons, while keeping energetic disorder small. Admittance spectroscopy measurements reveal that the material has indeed a high electron mobility and a small Poole−Frenkel slope, supporting our conclusions. By linking electronic structure, molecular packing, and mobility, we provide a pathway to the rational design of hosts with high charge mobilities.

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Section: Resultsmentioning

confidence: 99%

Design Rules for Charge-Transport Efficient Host Materials for Phosphorescent Organic Light-Emitting Diodes

et al. 2012

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“…Reference source not found. is extremely general as it can be reduced to Miller-Abrahams [18], Marcus [16], Marcus-LevichJortner [17] or Vukmirovic [15] rates when the appropriate limits are taken.…”

Section: B Exp a E K T  mentioning

confidence: 99%

How Many Parameters Actually Affect the Mobility of Conjugated Polymers?

2017

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We describe charge transport along a polymer chain with a generic theoretical model depending in principle on tens of parameters, reflecting the chemistry of the material. The charge carrier states are obtained from a model Hamiltonian that incorporates different types of disorder and electronic structure (e.g. the difference between homoand co-polymer). The hopping rate between these states is described with a general rate expression, which contains the rates most used in the literature as special cases. We demonstrate that the steady state charge mobility in the limit of low charge density and low field ultimately depends on only two parameters: an effective structural disorder and an effective electron-phonon coupling, weighted by the size of the monomer. The results support the experimental observation [N. I. Craciun, J. Wildeman, and P. W. M. Blom, Phys. Rev. Lett. 2008, 100, 056601] that the mobility in a broad range of (polymeric) semiconductors follows a universal behaviour, insensitive to the chemical detail.

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“…To establish whether this is the case, we have calculated the temperature dependence of the hole mobility in P3HT polymer (in the limit of low carrier concentration) using the multiscale methodology introduced in Ref. 17. In Fig.…”

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Carrier hopping in disordered semiconducting polymers: How accurate is the Miller–Abrahams model?

Vukmirović

Wang

2010

Applied Physics Letters

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We performed direct calculations of carrier hopping rates in strongly disordered conjugated polymers based on the atomic structure of the system, the corresponding electronic states and their coupling to all phonon modes. We found that the dependence of hopping rates on distance and the dependence of the mobility on temperature are significantly different than the ones stemming from the simple Miller-Abrahams model, regardless of the choice of the parameters in the model. A model that satisfactorily describes the hopping rates in the system and avoids the explicit calculation of electron-phonon coupling constants was then proposed and verified. Our results indicate that, in addition to electronic density of states, the phonon density of states and the spatial overlap of the wavefunctions are the quantities necessary to properly describe carrier hopping in disordered conjugated polymers.The carrier mobility of conjugated polymer materials is the most important physical property 1-6 for their application in organic electronic devices. Realistic polymer materials contain both crystalline (ordered) and amorphous (disordered) regions.7 Charge carrier transport is often limited by the presence of amorphous regions. In these regions the electronic states are localized due to presence of disorder and carrier transport takes place by phononassisted carrier hopping 8 between localized states. Such transport is traditionally modeled by assuming a certain density of electronic states in energy and space and a certain form of hopping probabilities between them.6,9-12 Different models are distinguished by the electronic density of states (DOS) assumed in the model, which is usually the tail of the Gaussian 9,10,12 or the exponential 11 distribution. The transition rates are typically assumed to decay exponentially with the distance between localized states, 9-12 in the Miller-Abrahams (MA) form.13 Free parameters that appear in the models are fitted to the experimental mobility measurements.From the applications of such models, it is widely understood that the mobility of the material strongly depends on the electronic DOS which is therefore believed to be the most important material property when charge transport is concerned.14 On the other hand, much less effort has been put into understanding how different forms of the transition rates affect the transport and in particular whether the MA expression is suitable at all. To address these questions, in this letter we perform direct ab-initio calculations of the transition rates between electronic states starting from atomic structure of the system, followed by explicit calculation of electronic state wavefunctions and their coupling to phonons. We find strong deviations of the transition rate dependence on distance from the MA form and analyze the consequences of this on electronic transport.Electronic structure calculations were performed using the plane wave pseudopotential approach and the charge patching method for organic systems introduced in Ref. 15 which gives the ac...

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Charge Carrier Motion in Disordered Conjugated Polymers: A Multiscale Ab Initio Study

Cited by 86 publications

References 35 publications

Design Rules for Charge-Transport Efficient Host Materials for Phosphorescent Organic Light-Emitting Diodes

Design Rules for Charge-Transport Efficient Host Materials for Phosphorescent Organic Light-Emitting Diodes

How Many Parameters Actually Affect the Mobility of Conjugated Polymers?

Carrier hopping in disordered semiconducting polymers: How accurate is the Miller–Abrahams model?

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