Magnetoresistance in organic light-emitting diode structures under illumination

Desai, Pratik; Shakya, P.; Kreouzis, Theo; Gillin, W. P.

doi:10.1103/physrevb.76.235202

Cited by 151 publications

(139 citation statements)

References 16 publications

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“…Moreover, various OMAR-related phenomena are claimed to be observed in literature, like spin mixing by a difference in g factors of electrons and holes 7,8 or high-field effects caused by triplet excitons. [9][10][11] Also in those cases, we feel that a more explicit quantum-mechanical treatment would be benificial.…”

Section: Introductionmentioning

confidence: 98%

Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors

et al. 2011

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The stochastic Liouville equation is applied to the field of organic magnetoresistance to perform detailed microscopic calculations on the different proposed models. By adapting this equation, the influence of a magnetic field on the current in bipolaron, electron-hole pair, and triplet models is calculated. The simplicity and wide applicability of the stochastic Liouville equation makes it a powerful tool for interpreting experimental results on magnetoresistance measurements in organic semiconductors. New insights are gained on the influence of hopping rates and disorder on the magnetoresistance.

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Section: Introductionmentioning

confidence: 98%

Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors

et al. 2011

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“…The largest magnetoresistance occurs when k hop is much smaller than ω hf , and this "slow-hopping" case is the case we consider from now on. The observation of large magnetic field effects in organic semiconductors [1][2][3][4][5][6][7][8][9][10] indicates that the hopping rate can indeed be smaller than or at least comparable to the hyperfine precession frequency. Because coherent effects between eigenstates of the spin Hamiltonian vanish in the limit of slow hopping, we only need to consider the occupancy of the (localized) spin eigenstates and hopping between these states.…”

Section: Modelmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8][9][10] The precise mechanisms behind these effects are still debated, but agreement is arising that the effects are caused by the magnetic-field sensitivity of spin-selective reactions between spin-carrying electronic excitations (electrons, holes, triplet excitons). Striking analogies exist with mechanisms known in the field of spin chemistry.…”

Section: Introductionmentioning

confidence: 99%

“…9,10,15 Spin-selective reactions between electrons and holes as well as between electrons or holes and triplet excitons have also been suggested to be responsible for magnetic field effects in the current. [3][4][5] A magnetic field effect in the current is usually interpreted as a magnetoresistance. The reported magnetoresistance of present organic devices is of the order of 10% at rather high electric fields.…”

Section: Introductionmentioning

confidence: 99%

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Route towards huge magnetoresistance in doped polymers

Kersten¹,

Meskers²,

Bobbert³

2012

Phys. Rev. B

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Room-temperature magnetoresistance of the order of 10% has been observed in organic semiconductors. We predict that even larger magnetoresistance can be realized in suitably synthesized doped conjugated polymers. In such polymers, ionization of dopants creates free charges that recombine with a rate governed by a competition between an applied magnetic field and random hyperfine fields. This leads to a spin-blocking effect that depends on the magnetic field. We show that the combined effects of spin blocking and charge blocking, the fact that two free charges cannot occupy the same site, lead to a magnetoresistance of almost two orders of magnitude. This magnetoresistance occurs even at vanishing electric field and is therefore a quasiequilibrium effect. The influences of the dopant strength, energetic disorder, and interchain hopping are investigated. We find that the dopant strength and energetic disorder have only little influence on the magnetoresistance. Interchain hopping strongly decreases the magnetoresistance because it can lift spin-blocking and charge-blocking configurations that occur in strictly one-dimensional transport. We provide suggestions for realization of polymers that should show this magnetoresistance.

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“…For CT-mediated processes, MFEs require that the observed physical property depends either directly or indirectly on the spin state of the electron-hole pair. For instance, spin selection rules for radiative electron-hole recombination can give rise to a magnetic field-dependent electroluminescence yield [20,[24][25][26]. To understand specifically how CT state properties are influenced by the presence of a magnetic field it is natural to describe the spin state of the electron-hole pair in a standard basis of singlet and triplet states.…”

mentioning

confidence: 99%

A Model of Charge-Transfer Excitons: Diffusion, Spin Dynamics, and Magnetic Field Effects

Lee

Shi

Willard

2016

J. Phys. Chem. Lett.

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In this letter we explore how the microscopic dynamics of charge transfer (CT) excitons are influenced by the presence of an external magnetic field in disordered molecular semiconductors. This influence is driven by the dynamic interplay between the spin and spatial degrees of freedom of the electron-hole pair. To account for this interplay we have developed a numerical framework that combines a traditional model of quantum spin dynamics with a stochastic coarse-grained model of charge transport. This combination provides a general and efficient methodology for simulating the effects of magnetic field on CT state dynamics, therefore providing a basis for revealing the microscopic origin of experimentally observed magnetic field effects. We demonstrate that simulations carried out on our model are capable of reproducing experimental results as well as generating theoretical predictions related to the efficiency of organic electronic materials.1 arXiv:1603.08160v2 [physics.chem-ph] Apr 2016Charge transfer (CT) states play a fundamental role in mediating interconversion between bound electronic excitations and free charge carriers in organic electronic materials.For processes that require this interconversion, such as electroluminescence in organic light emitting diodes (OLEDs) and photocurrent generation in organic photovoltaics (OPVs), low-energy (thermalized) CT states are often implicated as a precursor to efficiency loss pathways [1][2][3][4][5][6][7][8][9][10][11][12]. Despite this, much remains to be understood about the properties of CT states and how they contribute to various energy loss mechanisms. Due to their short lifetime and low optical activity, attempts to interrogate CT states directly have brought limited success. Notably, however, recent experiments that probe CT states indirectly via their response to an applied magnetic field have demonstrated the potential to reveal new information about this elusive class of excited states [13][14][15][16][17][18][19][20][21]. Unfortunately, extracting this information is challenging because it is encoded by a complex interplay of electronic and nuclear spin dynamics [15,22,23]. This interplay is further complicated when the dynamics of the electron-hole spin state (or the specific experimental observable) is coupled to a source of fluctuating microscopic disorder such as charge transport or molecular conformational dynamics [21]. In this letter we focus on disentangling this interplay.The dependence of an experimental observable on an applied magnetic field is generically referred to as the magnetic field effect (MFE). For CT-mediated processes, MFEs require that the observed physical property depends either directly or indirectly on the spin state of the electron-hole pair. For instance, spin selection rules for radiative electron-hole recombination can give rise to a magnetic field-dependent electroluminescence yield [20,[24][25][26]. To understand specifically how CT state properties are influenced by the presence of a magnetic field it is na...

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Magnetoresistance in organic light-emitting diode structures under illumination

Cited by 151 publications

References 16 publications

Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors

Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors

Route towards huge magnetoresistance in doped polymers

A Model of Charge-Transfer Excitons: Diffusion, Spin Dynamics, and Magnetic Field Effects

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