Magnetoelectroluminescence in organic light-emitting diodes

Lawrence, Joseph E.; Lewis, Alan M.; Manolopoulos, David E.; Hore, P. J.

doi:10.1063/1.4953093

Cited by 24 publications

(35 citation statements)

References 35 publications

(105 reference statements)

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“…This is highly unusual as such polaron transport characteristics are typically associated with organic materials. 23,24 Invoking Holstein's theory for small polarons 25 we present a transport model that relies on the co-existence of itinerant and localized polarons. Electronic structure calculations are also performed to investigate the structural and electronic characteristics in Ag 2 ZnSnSe 4 and Cu 2 ZnSnSe 4 for a better comparative understanding of their properties.…”

Section: Introductionmentioning

confidence: 99%

Polaronic transport in Ag-based quaternary chalcogenides

Wei

Khabibullin

Stedman

et al. 2017

Journal of Applied Physics

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Low temperature resistivity measurements on dense polycrystalline quaternary chalcogenides Ag 2þx Zn 1-x SnSe 4 , with x ¼ 0, 0.1, and 0.3, indicate polaronic type transport which we analyze employing a two-component Holstein model based on itinerant and localized polaron contributions. Electronic structure property calculations via density functional theory simulations on Ag 2 ZnSnSe 4 for both energetically similar kesterite and stannite structure types were also performed in order to compare our results to those of the compositionally similar but well known Cu 2 ZnSnSe 4. This theoretical comparison is crucial in understanding the bonding that results in polaronic type transport for Ag 2 ZnSnSe 4 , as well as the structural and electronic properties of both crystal structure types. In addition to possessing this unique electronic transport, the thermal conductivity of Ag 2 ZnSnSe 4 is low and decreases with increasing silver content. This work reveals unique structure-property relationships in materials that continue to be of interest for thermoelectric and photovoltaic applications.

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Section: Introductionmentioning

confidence: 99%

Polaronic transport in Ag-based quaternary chalcogenides

Wei

Khabibullin

Stedman

et al. 2017

Journal of Applied Physics

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“…the same "W" shaped ultra-small field MFE as presented experimentally despite a range of different model conditions 23,24,31,32,36,37 . The polaron pair model takes considerations of different interactions (e.g.…”

mentioning

confidence: 60%

“…The two hyperfine fields (two-proton) polaron pair model has been used in explaining the MFEs in OLEDs 10,23 . The polaron pair model has been successful in qualitatively describing ultra-small magnetic field effects 10,31,33 , and the model has been greatly developed in the past decade 23,24,31,32,36,37 . Here, in order to demonstrate the fitting process of the polaron pair model, a general and simplified two hyperfine field polaron pair model is applied here for the convenience of the fitting, where a reduced stochastic Liouville von Neumann equation is applied, compared to that used in some theoretical works 23,24,31,32,36,37 .…”

Section: Two Hyperfine Fields (Two-proton) Polaron Pair Modelmentioning

confidence: 99%

“…Further developments are required for the current simplified theoretical model for higher accuracy of the yielding parameters, for example, the inclusions of other possible quantum interactions (exchange interaction, triplet-polaron quenching, etc. ), a more comprehensive stochastic Liouville equation as modelled from literature 23,24,31,32,36,37 , and an alternative modelling for steady-state charge pair dynamics 54 , etc.…”

Section: Model Fitting and Analysismentioning

confidence: 99%

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Fitting the magnetoresponses of the OLED using polaron pair model to obtain spin-pair dynamics and local hyperfine fields

Weng

Gillin

Kreouzis

2020

Sci Rep

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Organic light-emitting diode (OLED) displays a sign reversal magnetic field effect (MFE) when the applied magnetic field range is reduced to the sub-milliTesla range and the Polaron Pair Model has been successful in explaining the ultra-small MFE. Here, we obtained high resolution (~ 1 µT) magnetoconductance (MC) and magnetoelectroluminescence (MEL) of a tris-(8-hydroxyquinoline)aluminium-based (Alq3) OLED within the magnetic field range of ± 500 µT with the earth magnetic field components cancelled. A clear “W” shaped MC with a dip position of ± 250 µT and a monotonic MEL were observed. We demonstrate a fitting technique using the polaron pair model to the experimentally obtained MC and MEL. The fitting process extracts physically significant parameters within a working OLED: the local hyperfine fields for electron and hole in Alq3: Bhf1 = (0.63 ± 0.01) mT (electron), Bhf2 = (0.24 ± 0.01) mT (hole); the separation rates for singlet and triplet polaron pairs: kS,s = (44.59 ± 0.01) MHz, kT,s = (43.97 ± 0.01) MHz, and the recombination rate for singlet polaron pair kS,r = (88 ± 6) MHz. The yielded parameters are highly reproducible across different OLEDs and are in broad agreement with density functional theory (DFT) calculations and reported experimental observations. This demonstrates the feasibility of this fitting technique to approach any working OLED for obtaining significant microscopic parameters.

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“…This new method is routinely applicable to radical pairs with as many as 20 or so hyperfine-coupled nuclear spins, which is the typical size of radical pair encountered in experimental studies of molecular wires. 1,2,[12][13][14][15][16][17] It has also been shown to be more reliable than the various semiclassical approximations [18][19][20][21] that can be applied to the problem. 11 In this paper, we shall exploit our new method by applying it to the PTZ •+ -Ph n -PDI •− molecular wires studied by Weiss et al, 15 which consist of a phenothiazine (PTZ) donor, a perylene-3,4:9,10-bis(dicarboximide) (PDI) acceptor, and a bridge of n para-phenylene rings.…”

Section: Introductionmentioning

confidence: 99%

Spin-dependent charge recombination along para-phenylene molecular wires

Fay

Lewis

Manolopoulos

2017

The Journal of Chemical Physics

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We have used an efficient new quantum mechanical method for radical pair recombination reactions to study the spin-dependent charge recombination along PTZ •+ -Phn-PDI •− molecular wires. By comparing our results to the experimental data of E. Weiss et al. [J. Am. Chem. Soc. 126, 5577 (2004)], we are able to extract the spin-dependent (singlet and triplet) charge recombination rate constants for wires with n = 2 − 5. These spin-dependent rate constants have not been extracted previously from the experimental data because they require fitting its magnetic field-dependence to the results of quantum spin dynamics simulations. We find that the triplet recombination rate constant decreases exponentially with the length of the wire, consistent with the superexchange mechanism of charge recombination. However, the singlet recombination rate constant is nearly independent of the length of the wire, suggesting that the singlet pathway is dominated by an incoherent hopping mechanism. A simple qualitative explanation for the different behaviours of the two spin-selective charge recombination pathways is provided in terms of Marcus theory. We also find evidence for a magnetic field-independent background contribution to the triplet yield of the charge recombination reaction, and suggest several possible explanations for it. Since none of these explanations is especially compelling given the available experimental evidence, and since the result appears to apply more generally to other molecular wires, we hope that this aspect of our study will stimulate further experimental work.

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Magnetoelectroluminescence in organic light-emitting diodes

Cited by 24 publications

References 35 publications

Polaronic transport in Ag-based quaternary chalcogenides

Polaronic transport in Ag-based quaternary chalcogenides

Fitting the magnetoresponses of the OLED using polaron pair model to obtain spin-pair dynamics and local hyperfine fields

Spin-dependent charge recombination along para-phenylene molecular wires

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