Influence of doping on spin-dependent exciton formation in Alq3 based OLEDs

Castro, Fernando A.; Silva, George B.; Nüesch, Frank; Zuppiroli, L.; Graeff, Carlos Frederico de Oliveira

doi:10.1016/j.orgel.2006.06.007

Cited by 13 publications

(14 citation statements)

References 17 publications

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“…In the bipolaron model one possible explanation is that rubrene is changing the balance of bipolarons/polaron population. Rubrene acts as a hole trap in Alq 3 -based OLEDs [17,18]. In this way, one can suppose that it would affect mainly the positively charged bipolarons.…”

Section: Resultsmentioning

confidence: 99%

Magnetic field effects on the conductivity of organic bipolar and unipolar devices at room temperature

et al. 2010

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a b s t r a c tMagnetic field effects on the conductivity of different types of organic devices: undoped and dye doped aluminium (III) 8-hydroxyquinoline (Alq 3 )-based organic light emitting diodes (OLEDs), electrononly Alq 3 -based diodes, and a hole-only N,N -diphenyl-N,N -bis(1-naphthyl)-1,1 -biphenyl-4,4 -diamine (␣-NPD)-based diode were studied at room temperature. Only negative magnetoresistance (MR) was observed for the Alq 3 -based devices. The addition of a rubrene dye in Alq 3 -based OLEDs quenches the MR by a factor of 5. The ␣-NPD hole-only device showed only positive MR. Our results are discussed with respect to the actual models for MR in organic semiconductors. Our results are in good agreement with the bipolaron model.

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Section: Resultsmentioning

confidence: 99%

Magnetic field effects on the conductivity of organic bipolar and unipolar devices at room temperature

et al. 2010

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“…The agreement for Alq 3 is particularly encouraging, for the experimental data of Alq 3 are measured in device structures under working conditions. 43 The g-factor changes due to the SOC in organics are generally small, and similar in amplitude except those involving transition metal ions like Cu, where the g-factor deviation is large. It is worth pointing out that the g-factor deviation in Alq 3 is minute compared to its large spin admixture γ 2 .…”

Section: Real Organic Materialsmentioning

confidence: 99%

Spin-orbit coupling and its effects in organic solids

2012

Phys. Rev. B

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We present a detailed analysis of spin-orbit coupling (SOC) in π-conjugated organic materials and its effects on spin characteristics including the spin relaxation time, spin diffusion length, and g factor. While π electrons are responsible for low-energy electrical and optical processes in π-conjugated organic solids, σ electrons must be explicitly included to properly describe the SOC. The SOC mixes up-and down-spin states, and in the context of spintronics, can be quantified by an admixture parameter in the electron and hole polaron states in π-conjugated organics. Molecular geometry fluctuations such as ring torsion, which are common in soft organic materials and may depend on sample preparation, are found to have a strong effect on the spin mixing. The SOCinduced spin mixing leads to spin flips as polarons hop from one molecule to another, giving rise to spin relaxation and diffusion, which are examined by the time-dependent perturbation theory and density-matrix theory. The spin relaxation rate is found to be proportional to the carrier hopping rate, or equivalently, carrier mobility. The spin diffusion length depends on the spin mixing and hopping distance but is insensitive to the carrier mobility. An applied electric field causes spin drift and gives rise to upstream and downstream spin diffusion lengths in the hopping-conduction regime. The SOC influences the g factor of the polaron state and make it deviate from the free-electron value. The deviation is due to the mixing of different orbitals in the polaron state, which does not include the spin mixing within a same orbital, and therefore underestimates the SOC strength. In particular, the g factor is not sensitive to the molecular geometry fluctuations, where the spin mixing within a same orbital is dominant. The SOCs in tris-(8-hydroxyquinoline) aluminum (Alq3) and in copper phthalocyanine (CuPc) are particularly strong, due to the orthogonal arrangement of the three ligands in the former and Cu 3d orbitals in the latter. The theory quantitatively explains the recent measured spin diffusion lengths in Alq3 from muon spin rotation and in CuPc from spin-polarized two-photon photoemission.

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“…In fact, over the past years it has provided valuable insight into various transport and recombination processes in semiconductors. [6][7][8][9][10][11] In this work we have used EDMR and EPR to investigate emeraldine base polyaniline films. We observed a transition of the magnetic susceptibility dependence on temperature, from a linear decrease with increasing temperature ͑localized Curie spins͒ to a constant value ͑delocalized Pauli spins͒.…”

Section: Introductionmentioning

confidence: 99%

Electrically detected and conventional magnetic resonance investigation of surface and bulk states in polyaniline thin films

Castro

Graeff

2007

Journal of Applied Physics

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Electrically detected magnetic resonance ͑EDMR͒ and electron paramagnetic resonance ͑EPR͒ were used to investigate emeraldine base polyaniline films. The magnetic susceptibility presented a Curie ͑localized spins͒-Pauli ͑delocalized spins͒ transition at 240 K, when we also observed a transition in the dependence of the g factor with temperature ͑T͒. Peak-to-peak linewidth decreases with increasing temperature, reflecting that motional narrowing limits the hyperfine and dipolar broadening in this polymer. EDMR spectra could only be observed above 250 K in accordance to EPR results. Surface and bulk transport could be separated and their analysis reflected the effect of magnetic interaction with oxygen.

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Influence of doping on spin-dependent exciton formation in Alq3 based OLEDs

Cited by 13 publications

References 17 publications

Magnetic field effects on the conductivity of organic bipolar and unipolar devices at room temperature

Magnetic field effects on the conductivity of organic bipolar and unipolar devices at room temperature

Spin-orbit coupling and its effects in organic solids

Electrically detected and conventional magnetic resonance investigation of surface and bulk states in polyaniline thin films

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