Revealing weak spin-orbit coupling effects on charge carriers in a 
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-conjugated polymer

Malissa, H.; Miller, R.; Baird, Douglas; Jamali, S.H.; Joshi, Gajadhar; Bursch, Markus; Tol, Johan van; Lupton, John M.; Boehme, Christoph

doi:10.1103/physrevb.97.161201

Cited by 26 publications

(52 citation statements)

References 53 publications

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“…We have obtained significantly different values for the two local hyperfine fields, mT and mT experienced by the electron and hole forming the polaron pair. This notable difference between the electron and the hole local hyperfine fields was also observed experimentally from literature 32 , 41 , 44 , 45 . The polarons are experiencing different local hyperfine fields despite both being localized on an Alq 3 molecule.…”

Section: Model Fitting and Analysissupporting

confidence: 84%

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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Section: Model Fitting and Analysissupporting

confidence: 84%

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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“…This is consistent with the conclusion of the recent report drawn from a comparison of the measured and simulated EDMR spectra in the high-magnetic field EDMR for the OLED of 2-methoxy, 5-(2 0 -ethyl-hexyloxy)-(MEH-) PPV. 34 In the model of EDMR and ELDMR considering the spindependent reaction of e-h pairs, 35,36 an equilibrium relation is assumed to hold among free polaron carriers, e-h pairs, and excitons. An ESR transition occurring at sublevels of triplet e-h pair (TP) slightly changes the density-ratio between singlet e-h pair (SP) and TP through spin-mixing of S and T 0 .…”

Section: Journal Of Applied Physicsmentioning

confidence: 99%

Correlation between bias-dependent ESR signals and magnetic field effects in organic light emitting diodes

Kanemoto

Hatanaka

Suzuki

2019

Journal of Applied Physics

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The bias dependent behaviors in magnetic field effects (MFEs) of the current and the electroluminescence (EL) intensity in organic light emitting diodes (OLEDs) have been investigated from electrically-detected and EL-detected magnetic resonance (EDMR and ELDMR) techniques. An EDMR signal was not detected from the electron-only device, and the hole-only device gave only a much smaller EDMR signal than the OLED device. Both the EDMR and ELDMR signals observed from the OLED are concluded to primarily arise from the spin-dependent reaction of electron-hole (e-h) pairs. Both the normalized EDMR and ELDMR signal intensities decrease by increasing the operation bias of OLED, because the increased bias enhances the dissociation and recombination of e-h pairs beyond the increase in the pair-density by the bias. The bias-dependence curves of magneto-conductances and magneto-EL intensities are demonstrated to be very similar to those of the normalized EDMR and ELDMR, respectively. This similarity gives direct evidence that e-h pairs determine the MFEs of the present OLEDs at room temperature and that the MFEs are reduced by bias-dependent dissociation and recombination of e-h pairs. The bias-dependent EDMR and ELDMR experiments are thus effective as probing methods to examine the magnetic field properties via e-h pairs of OLEDs.

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“…Note that, given the exceedingly weak spin-orbit coupling of the organic semiconductor material used in the experiments discussed in the following, the spin Hamiltonian is perfectly defined without an explicit spin-orbit term, using effective Landé g-factors instead. We direct the interested reader to a recent joint experimental and theoretical examination of the influence of spin-orbit coupling in these materials 14 . Although all these interactions are time independent, the local hyperfine fields and the dipolar interaction are taken to be random and different for different configurations.…”

Section: Resultsmentioning

confidence: 99%

“…It is important to stress that such studies are only possible in materials characterized by very weak spin-orbit coupling 14 , such as organic semiconductors, and are not generic to electron-hole recombination in LEDs as a whole. In an inorganic LED, for example, spin mixing occurs by spin-orbit coupling in addition to the fact that recombination does usually not occur into tightly bound, and hence thermally stable, excitonic species.…”

Section: Introductionmentioning

confidence: 99%

Floquet spin states in OLEDs

et al. 2021

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Electron and hole spins in organic light-emitting diodes constitute prototypical two-level systems for the exploration of the ultrastrong-drive regime of light-matter interactions. Floquet solutions to the time-dependent Hamiltonian of pairs of electron and hole spins reveal that, under non-perturbative resonant drive, when spin-Rabi frequencies become comparable to the Larmor frequencies, hybrid light-matter states emerge that enable dipole-forbidden multi-quantum transitions at integer and fractional g-factors. To probe these phenomena experimentally, we develop an electrically detected magnetic-resonance experiment supporting oscillating driving fields comparable in amplitude to the static field defining the Zeeman splitting; and an organic semiconductor characterized by minimal local hyperfine fields allowing the non-perturbative light-matter interactions to be resolved. The experimental confirmation of the predicted Floquet states under strong-drive conditions demonstrates the presence of hybrid light-matter spin excitations at room temperature. These dressed states are insensitive to power broadening, display Bloch-Siegert-like shifts, and are suggestive of long spin coherence times, implying potential applicability for quantum sensing.

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Revealing weak spin-orbit coupling effects on charge carriers in a π -conjugated polymer

Cited by 26 publications

References 53 publications

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

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

Correlation between bias-dependent ESR signals and magnetic field effects in organic light emitting diodes

Floquet spin states in OLEDs

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