Understanding and predicting the orientation of heteroleptic phosphors in organic light-emitting materials

Jurow, Matthew J.; Mayr, Christian; Schmidt, Tobias D.; Lampe, Thomas; Djurovich, Peter I.; Brütting, Wolfgang; Thompson, Mark E.

doi:10.1038/nmat4428

Cited by 226 publications

(212 citation statements)

References 54 publications

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“…Recently, such alignment has been observed for several emitters 4 and was correlated with the permanent molecular dipole moments 4 , a strong formation of supra molecules due to an alignment of the triplet excited states within the host 5 , or the alignment of anisotropic molecules at the thin film surface during deposition 6 . Resulting efficiency enhancements have been reported for both phosphorescent guest-host systems 1, 2 as well as emitters exhibiting delayed fluorescence 7–9 .…”

Section: Introductionmentioning

confidence: 88%

Plasmonic Purcell effect reveals obliquely ordered phosphorescent emitters in Organic LEDs

Ciarnaín

Michaelis

Wehlus

et al. 2017

Sci Rep

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The non-isotropic alignment of molecules can increase the interaction efficiency with propagating light fields. This applies to both emissive and absorptive systems and can be exploited for achieving unprecedented efficiencies of organic opto-electronic devices such as organic light-emitting diodes. Optical analysis has revealed certain phosphorescent emitters to align spontaneously in an advantageous orientation. Unfortunately, established approaches only determine an average orientation because emission patterns solely depend on the second moments of the transition dipole vector distribution. In order to resolve further details of such a distribution, additional differences in the emission characteristics of parallel and perpendicularly oriented emitters need to be introduced. A thin metal layer near the emitters introduces plasmon mediated losses mostly for perpendicular emitters. Then, analyzing the emission at different polarizations allows one to measure emission lifetimes of mostly parallel or mostly perpendicular oriented emitters. This should alter the transient emission when observing the temporal phosphorescence decay under different directions and/or polarizations. The angular width of the orientation distribution can be derived from the degree of such lifetime splitting. Our results suggest a narrow but obliquely oriented molecular ensemble of Ir(MDQ)2(acac) doped into the α-NPD host inside an Organic LED stack.

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Section: Introductionmentioning

confidence: 88%

Plasmonic Purcell effect reveals obliquely ordered phosphorescent emitters in Organic LEDs

Ciarnaín

Michaelis

Wehlus

et al. 2017

Sci Rep

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“…[89,90] Molecular dynamics simulations of the deposition and surface rearrangement processes at the substrate surface can be used to model some aspects of the growth process, such as collective effects (see Figure 2c). [89,90] Molecular dynamics simulations of the deposition and surface rearrangement processes at the substrate surface can be used to model some aspects of the growth process, such as collective effects (see Figure 2c).…”

Section: Morphologymentioning

confidence: 99%

Toward Design of Novel Materials for Organic Electronics

et al. 2019

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organic/inorganic perovskites solar cells [6] to printable electronic circuits based on organic field-effect transistors (OFETs). [7] While OLED displays outperform their inorganic counterparts in terms of energy efficiency, [8] scientific and technical challenges concerning the stability and processability of the organic materials used in large-area OLEDs and organic solar cells remain. New challenges arise from applications, such as displays on flexible substrates, OLED lightning, large area displays as well as for printable or solution processable larger area solar cells. [8] Many of the remaining challenges are material related, e.g., the low mobility of charge carriers in organic materials in general and in amorphous organic semiconductors in particular. There are other materials related issues, such as limited OLED life times due to unstable blue hosts and emitters, [9] low fill factors, and therefore reduced power conversion efficiencies of organic solar cells, [10,11] low conductivity and high costs of organic charge transport layers of perovskite solar cells [6,12,13] and low conductivity and hard processability of crystalline OFET materials. [14] Conductivity and injection can be improved by doping the organic thin films with molecular dopants with high electron affinities (p-type) [15] or low ionization energies (n-type). [16] The doping mechanism of organic materials is in many cases not well understood, [17] making material and device optimization a costly experimental endeavor.The development of better materials is presently based on chemical insight, in part guided by theoretical understanding, or the experimental screening of large numbers of compounds. Given the size of the potentially available chemical space this remains a costly and time-consuming approach. Recent successes in experimental design of novel materials and concepts include the development of a stable strong molecular n-type dopant, [16] a study about the quantitative relation between interaction parameter, miscibility, and function of conjugated polymer donors and small-molecule acceptors for bulk heterojunctions as used in organic solar cells [18] the development of a universal strategy for ohmic hole injection into organic semiconductors with high ionization energies [19] and many others. [20][21][22][23][24][25] Another example is the development of strategies to harvest triplet excitons in organic light emitting diodes. For this purpose, novel classes of emitter molecules were developed, which include thermally activated delayed fluorescence (TADF)-based molecules, [26][27][28][29][30][31][32] rotationally accessed spin-state inversion, [33] and radical-based emitters. [34] Materials for organic electronics are presently used in prominent applications, such as displays in mobile devices, while being intensely researched for other purposes, such as organic photovoltaics, large-area devices, and thin-film transistors. Many of the challenges to improve and optimize these applications are material related and there is a nearly inf...

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“…The orientation of various emitter molecules has been investigated and many compounds exhibiting a preferential horizontal orientation have been found. However, the origin of their preferred orientation is still under debate [5][6][7].…”

Section: Introductionmentioning

confidence: 99%