Traps and trions as origin of magnetoresistance in organic semiconductors

Cox, M Matthijs; Janssen, Pieter; Zhu, Feng; Koopmans, B.

doi:10.1103/physrevb.88.035202

Cited by 47 publications

(78 citation statements)

References 48 publications

(65 reference statements)

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“…We attribute the MFEs to the recently proposed trion mechanism. 23 We analyzed the MC(V)-curves using the analytical model as proposed by Cox et al and confirmed the physical validity of the fitting parameters. The linewidths of the low-field effects have been analyzed and we show that the hyperfine field strength B hf is almost identical for all measurements, whereas B m and r do show a remarkable voltage and temperature dependence.…”

Section: Discussionmentioning

confidence: 99%

“…Finally, it was shown that the magnetic field effect on the current in pristine organic semiconductors is predominantly governed by the reactions between triplet excitons and polarons. 18,20,22,23,25 Moreover, Cox et al recently proposed an analytical model where these reactions are described by the spin-selective formation of socalled metastable trions from triplet exciton-polaron pairs. 23 Their model provides an intuitive explanation of the MC(V) dependence.…”

Section: B Magnetic Field Effectsmentioning

confidence: 99%

“…18,20,22,23,25 Moreover, Cox et al recently proposed an analytical model where these reactions are described by the spin-selective formation of socalled metastable trions from triplet exciton-polaron pairs. 23 Their model provides an intuitive explanation of the MC(V) dependence. The initial increase originates from the increase of triplet density with voltage, while the eventual decrease can be assigned to a saturation of trap filling.…”

Section: B Magnetic Field Effectsmentioning

confidence: 99%

“…It was demonstrated before that in organic light emitting diode (OLED) type devices, the MFEs are dominated by the reactions between (trapped) triplets and polarons. 18,22,23 A schematic overview of this mechanism is shown in Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

“…We can distinguish between the rates of dissociation and recombination of singlet and triplet electron-hole pairs (q S,T and k S,T ) or doublet and quartet triplet-polaron pairs (r D,Q and k D,Q ), respectively. 23 The low magnetic field effect (LFE) originates from mixing of precursor pairs by hyperfine fields (hf); whereas the mixing of triplet exciton-polaron pairs at the zero field splitting field scale (ZFS) leads to a high-field effect (HFE). By studying the MFE lineshapes as a function of voltage and temperature, we obtain a deeper understanding of these triplet-polaron reactions.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Unraveling the temperature and voltage dependence of magnetic field effects in organic semiconductors

Janssen¹,

Wouters²,

Cox³

et al. 2013

Journal of Applied Physics

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Articles you may be interested inStudy of poly(3-hexylthiophene)/cross-linked poly (vinyl alcohol) In recent years, it was discovered that the current through an organic semiconductor, sandwiched between two non-magnetic electrodes, can be changed significantly by applying a small magnetic field. This surprisingly large magnetoresistance effect, often dubbed as organic magnetoresistance (OMAR), has puzzled the young field of organic spintronics during the last decade. Here, we present a detailed study on the voltage and temperature dependence of OMAR, aiming to unravel the lineshapes of the magnetic field effects and thereby gain a deeper fundamental understanding of the underlying microscopic mechanism. Using a full quantitative analysis of the lineshapes, we are able to extract all linewidth parameters and the voltage and temperature dependencies are explained with a recently proposed trion mechanism. Moreover, explicit microscopic simulations show a qualitative agreement to the experimental results. V C 2013 AIP Publishing LLC.

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Section: Discussionmentioning

confidence: 99%

Section: B Magnetic Field Effectsmentioning

confidence: 99%

Section: B Magnetic Field Effectsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Unraveling the temperature and voltage dependence of magnetic field effects in organic semiconductors

Janssen¹,

Wouters²,

Cox³

et al. 2013

Journal of Applied Physics

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Ultralarge Magneto‐Electroluminescence in Exciplex‐Based Devices Driven by Field‐Induced Reverse Intersystem Crossing

Lei

Zhang

Chen

et al. 2016

Advanced Optical Materials

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wileyonlinelibrary.com COMMUNICATIONis the PP lifetime and τ SL is the spin-lattice relaxation time. [ 20 ] In general, F substantially reduce the MEL value if τ / τ SL > 1. This may be the reason that MEL| max has been limited so far to ≈10%-20% in conventional (exciton-based) OLEDs. [ 21 ] One method for enhancing MEL| max in OLEDs is increasing τ SL , so that even weak spin-mixing interactions may still be effective in changing ρ with B . [ 20 ] Another way to increase MEL| max is by involving other spin-mixing channels that may not have an obvious upper bound for changing ρ . One such spin-mixing process is the so called reverse intersystem crossing (RISC) which is recently proposed by Adachi et al. in exciplex-based OLEDs. [ 22,23 ] Usually the RISC in exciplexOLEDs is thermally activated. [22][23][24] In the thermally activated RISC process, a large number of triplet exciplexes can convert into singlets assisted with thermal energy due to the small energy different (<50 meV) between the singlet and triplet exciplexes. [ 23,24 ] In this case, RISC process would provide an alternative spin-mixing channel to manipulate the ρ of singlet/triplet exciplexes, which is expected to induce large magnetic fi eld responses. Based on this concept, Basel et al. have reported large magneto-photoluminescence (≈5%) and MEL (≈35%) in electron donor-acceptor (D-A) blend exciplex-based OLEDs. [ 19 ] However, it should be emphasized that these values are still far away from the requirement for any sensor and/or display applications. In the meanwhile, Ling et al. have reported a much larger MEL (up to ≈110%) in another D-A combination exciplex-based OLEDs. [ 25 ] Unfortunately, the origin of such large MEL is quite obscure. Worsely, from the fundamental mechanism perspective, the critical factors that determine the magnitude of MEL| max in such D-A exciplex-based OLEDs are still missing. Therefore, it is desirable to get a more general understanding of MEL in such exciplex-based OLEDs and fi nd the way to achieve really high magnetic fi eld responses for some useful applications.In this communication, systematic studies on MEL in exciplex-OLEDs based on a series of D-A composites were reported as well as ultralarge MEL (up to ≈160%) and MC (as high as ≈115%) at room temperature. As will be demonstrated in detail in the following text that the crucial parameter that determines the MEL| max is activation energy ( E a ), which in turn is determined by the energy different between the singlet and triplet exciplexes (Δ E 1,3 DOI: 10.1002/adom.201600015The spin degree of freedom plays an important role in photophysical processes of organic light-emitting diodes (OLEDs) based on π-conjugated polymers and small molecules. [1][2][3] Therefore, application of an external magnetic fi eld, B , enables manipulation of the device current, dubbed magneto-conductivity (MC), as well as its electroluminescence (EL) emission intensity and dubbed magneto-electroluminescence (MEL). [4][5][6][7][8][9] When considering the MEL mechanism we note tha...

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Magnetic Field Enhancement of Organic Light‐Emitting Diodes Based on Electron Donor–Acceptor Exciplex

Basel

Sun

Baniya

et al. 2015

Adv Elect Materials

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Several methods of harvesting singlet excitons via delayed fl uorescence have been introduced in OLED so far. These methods include up-conversion to singlet excitons by triplet-triplet annihilation (TTA) [ 3,4 ] or triplet fusion in materials that show a strong singlet fi ssion. [ 5 ] A different approach for enhancing the singlet emission that involves triplet excitons was introduced recently, whereby the triplet excitons may undergo reverse intersystem crossing (RISC) to singlet excitons and consequently give rise to thermally activated delayed fl uorescence (TADF). [6][7][8][9][10][11][12] This occurs in compounds with small electron exchange energy, and thus small singlet-triplet energy splitting, Δ E ST that enables triplet excitons to undergo thermally activated RISC to the singlet manifold. [ 13 ] A fi rm indication for TADFrelated emission in compounds that possess RISC is that the EL in these OLED is thermally activated, with activation energy E act ≈ Δ E ST Ͻ Ͻ 0.7 eV (which is Δ E ST in traditional organic semiconductors). During the last few years there has been a large interest in magnetic fi eld effect (MFE) in conjugated organic compounds, mainly because of the possibility to enhance the electroluminescence effi ciency, which was dubbed magneto-EL (MEL). [ 11,[14][15][16][17][18][19][20][21] In this effect, the magnetic fi eld changes the exchange rate between PP singlet (PP S ) and triplet (PP T ), which can be detected through the induced change in the EL emission intensity (MEL) or the current density (MC) in the device. This occurs if the PP S and PP T recombination rates ( R S , R T ) and/or dissociation rates ( d S , d T ) differ from each other. [ 17,22 ] So far the MEL maximum value, MEL max at room temperature (RT) has been less than ≈20% in OLEDs.In conventional OLEDs, spin mixing occurs within the PP states rather than at the exciton levels because the electron-hole orbitals strongly overlap in the latter species leading to large exchange energy, J , that consequently causes large energy gap, Δ E ST (=2 J ) between singlet and triplet states. In contrast, materials showing RISC may allow spin-mixing among the PP spin levels and in the exciton levels because Δ E ST is small. [ 23 ] In this case, possible spin-mixing mechanism may be the hyperfi ne interaction [ 24,25 ] and/or the Δ g mechanism, [ 26 ] where the difference, Δ g in the g -values of positive and negative carrier in the pair may promote intersystem crossing. The obtained full width Reverse intersystem crossing (RISC) from triplet to singlet states has been recently introduced to photophysics of organic chromophores. One type of RISC occurs in donor (D)-acceptor (A) composites that form an exciplex manifold in which the energy difference, Δ E ST between the lowest singlet (S 1 ) and triplet (T 1 ) levels of the exciplex is small (<100 meV) thus allowing RISC at room temperature. This adds a delayed component to the photoluminescence emission that is widely known as thermally activated delayed fl uorescence. Here, it is found t...

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Traps and trions as origin of magnetoresistance in organic semiconductors

Cited by 47 publications

References 48 publications

Unraveling the temperature and voltage dependence of magnetic field effects in organic semiconductors

Unraveling the temperature and voltage dependence of magnetic field effects in organic semiconductors

Ultralarge Magneto‐Electroluminescence in Exciplex‐Based Devices Driven by Field‐Induced Reverse Intersystem Crossing

Magnetic Field Enhancement of Organic Light‐Emitting Diodes Based on Electron Donor–Acceptor Exciplex

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