Balanced ambipolar charge carrier mobility in mixed layers for application in hybrid white organic light-emitting diodes

Schwartz, Gregor; Ke, Tung Huei; Wu, Chung‐Chih; Walzer, Karsten; Leo, Karl

doi:10.1063/1.2973151

Cited by 72 publications

(62 citation statements)

References 14 publications

(15 reference statements)

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“…[10]. Agreement between the hole mobility in α-NPD extracted from device simulations and measured by TOF was reported previously by Schwartz et al [11]. In another TOF study of hole transport in α-NPD, the value σ = 0.090 eV was found from a fit to the GDM of the T dependence of the mobility [12], in excellent agreement with the value of σ = 0.087 eV.…”

Section: Introductionsupporting

confidence: 73%

Effects of energy correlations and superexchange on charge transport and exciton formation in amorphous molecular semiconductors: An ab initio study

et al. 2017

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Massé, A.; Friederich, P.; Symalla, F.; Liu, F.; Meded, V.; Coehoorn, R.; Wenzel, W.; Bobbert, P.A. Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication Citation for published version (APA):Massé, A., Friederich, P., Symalla, F., Liu, F., Meded, V., Coehoorn, R., ... Bobbert, P. A. (2017). Effects of energy correlations and superexchange on charge transport and exciton formation in amorphous molecular semiconductors: an ab initio study. Physical Review B, 95(11), 1-11. [115204]. DOI: 10.1103/PhysRevB.95.115204 General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. In this study, we investigate on the basis of ab initio calculations how the morphology, molecular on-site energies, reorganization energies, and charge transfer integral distribution affect the hopping charge transport and the exciton formation process in disordered organic semiconductors. We focus on three materials applied frequently in organic light-emitting diodes: α-NPD, TCTA, and Spiro-DPVBi. Spatially correlated disorder and, more importantly, superexchange contributions to the transfer integrals, are found to give rise to a significant increase of the electric field dependence of the electron and hole mobility. Furthermore, a material-specific correlation is found between the HOMO and LUMO energy on each specific molecular site. For α-NPD and TCTA, we find a positive correlation between the HOMO and LUMO energies, dominated by a Coulombic contribution to the energies. In contrast, Spiro-DPVBi shows a negative correlation, dominated by a conformational contribution. The size and sign of this correlation have a strong...

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Section: Introductionsupporting

confidence: 73%

Effects of energy correlations and superexchange on charge transport and exciton formation in amorphous molecular semiconductors: An ab initio study

et al. 2017

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“…Two prior studies have measured the charge carrier mobility of the electron transport materials Tris-(8-hydroxyquinoline)aluminum (AlQ 3 ) and bis(2-methyl-8-quinolinato)-4-phenylphenolate aluminum when mixed into N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine. 7,8 It was observed that increasing the fraction of the conductive material leads to a higher mobility, but no clear relation between concentration and mobility was identified. Subsequently, it was observed that the electrical properties of 4,7-diphenyl-1,10-phenanthroline (BPhen)/ tetracyanoquinodimethane (TCNQ) 9 and AlQ 3 /4,4 ′ -bis(carbazol-9-yl)-biphenyl (CBP) 10 mixed layers could be explained with an empirical scaling law:…”

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confidence: 99%

Link between hopping models and percolation scaling laws for charge transport in mixtures of small molecules

Kim

Baldo

2016

AIP Advances

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Mixed host compositions that combine charge transport materials with luminescent dyes offer superior control over exciton formation and charge transport in organic light emitting devices (OLEDs). Two approaches are typically used to optimize the fraction of charge transport materials in a mixed host composition: either an empirical percolative model, or a hopping transport model. We show that these two commonly-employed models are linked by an analytic expression which relates the localization length to the percolation threshold and critical exponent. The relation is confirmed both numerically and experimentally through measurements of the relative conductivity of Tris(4-carbazoyl-9-ylphenyl)amine (TCTA) :1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene (BmPyPb) mixtures with different concentrations, where the TCTA plays a role as hole conductor and the BmPyPb as hole insulator. The analytic relation may allow the rational design of mixed layers of small molecules for high-performance OLEDs.

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“…However, a blue fluorescent emitting layer (EML) needs to be close to the exciton recombination zone, because the diffusion length of singlet excitons is far below that of triplet excitons. 1,[11][12][13] Compared with the triplet level of yellow or green phosphorescent dopants, fluorescent materials such as p-bis (p-N,N-diphenyl-aminostyryl) benzene (DSA-ph), 4,4 0 -bis [2-{4-(N,N-diphenylamino) phenyl}vinyl]biphenyl (DPAVBi), and 2,2 0 ,7,7 0 -tetrakis(2,2-diphenylvinyl)spiro-9,9 0 -bifluorene (Spiro-DPVBi) [14][15][16][17][18] with a lower triplet level inevitably quench the triplet excitons in the exciton recombination zone, giving rise to low external quantum efficiencies (EQEs). In order to alleviate this negative effect, a kind of functional layer called interlayer has been employed in conventional hybrid WOLEDs.…”

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confidence: 99%

“…8,15,18,[23][24][25] The mixed interlayer can effectively prevent triplet quenching in a fluorescent emitter. Nevertheless, the proportions and the thicknesses of such a mixed interlayer have to be precisely controlled, which renders the device fabrication process both cumbersome and difficult to reproduce.…”

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confidence: 99%

“…In order to alleviate this negative effect, a kind of functional layer called interlayer has been employed in conventional hybrid WOLEDs. 8,15,[18][19][20][21][22][23][24][25] A single hole or electron transport layer can work as a simplest interlayer, 8,[19][20][21][22] which is easy to fabricate but cannot simultaneously provide sufficient blue emission by separating the fluorescent EML from the exciton recombination zone. Quenching can also occur in the triplet transfer process from the exciton recombination zone to the fluorescent emitter with a lower lying non-radiative triplet level.…”

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confidence: 99%

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Managing excitons for high performance hybrid white organic light-emitting diodes by using a simple planar heterojunction interlayer

Shi

Sun

et al. 2018

Applied Physics Letters

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High performance hybrid white organic light-emitting diodes (WOLEDs) were fabricated by inserting a planar heterojunction interlayer between the fluorescent and phosphorescent emitting layers (EMLs). The maximum external quantum efficiency (EQE) of 19.3%, current efficiency of 57.1 cd A−1, and power efficiency (PE) of 66.2 lm W−1 were achieved in the optimized device without any light extraction enhancement. At the luminance of 1000 cd m−2, the EQE and PE remained as high as 18.9% and 60 lm W−1, respectively, showing the reduced efficiency-roll. In order to disclose the reason for such high performance, the distribution of excitons was analyzed by using ultra-thin fluorescent and phosphorescent layers as sensors. It was found that the heterojunction interlayer can efficiently separate the singlet and triplet excitons, preventing the triplet excitons from being quenched by the fluorescent emitter. The introduction of the heterojunction interlayer between the fluorescent and phosphorescent EMLs should offer a simple and efficient route to fabricate the high performance hybrid WOLEDs.

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Balanced ambipolar charge carrier mobility in mixed layers for application in hybrid white organic light-emitting diodes

Cited by 72 publications

References 14 publications

Effects of energy correlations and superexchange on charge transport and exciton formation in amorphous molecular semiconductors: An ab initio study

Effects of energy correlations and superexchange on charge transport and exciton formation in amorphous molecular semiconductors: An ab initio study

Link between hopping models and percolation scaling laws for charge transport in mixtures of small molecules

Managing excitons for high performance hybrid white organic light-emitting diodes by using a simple planar heterojunction interlayer

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