Triplet-to-Singlet Exciton Formation in poly(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi></mml:math>-phenylene-vinylene) Light-Emitting Diodes

Li, Lin; Meng, Hsin‐Fei; Shy, Jow Tsong; Horng, Sheng Fu; Yu, L. S.; Chen, C. H.; Liaw, H. H.; Huang, Chung-Ping; Peng, Kang-Yung; Chen, S. A.

doi:10.1103/physrevlett.90.036601

Cited by 54 publications

(21 citation statements)

References 15 publications

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“…Thus, the singlet generation yield is a true constant and, in contrast to previous reports [90,91], we find no electric field dependence with the drive voltages we have used. From these plots both el / el = 0.069 ± 0.002 and opt / opt = 0.0058 ± 0.0002 for electrical and optical excitations, respectively, and consequently the el/opt ratio can be obtained, 11.9 ± 0.8.…”

Section: Isrn Materials Sciencecontrasting

confidence: 53%

“…Over the past few years, an increasing number of experimental reports make it clear that the 25% limit is broken [55][56][57][58][59]. In small-molecule-based OLEDs, original experimental evidence pointed to the 25% limit being obeyed [60,61], whereas in polymers this was not so; however, more recent reports, especially those from the OLED group in Kodak have shown that the 25% limit in small-molecule devices was also greatly exceeded [62,63].…”

Section: Exciton Formation In An Oledmentioning

confidence: 96%

“…Furthermore, the implied equivalence of optically and electrically excited excitons in these experiments may not hold true [88], given the fact that common phosphorescent acceptors are electron traps and thus act as recombination centres only during electrical excitation [89]. Apart from such indirect materials approaches, experiments that directly probe the number of singlet and triplet excitons formed from charge carrier recombination are generally more convincing and transparent [90]. Attempts to determine absolute values are certainly unrealistic [56,91,92], given the experimental difficulties in collecting all the emission from a device, especially waveguided light, and the difficulty in measuring the true current which yields light generation rather than IR losses in the ITO and capacitance effects, are unknown.…”

Section: Experimental Observationsmentioning

confidence: 99%

“…This also shows that for singlet excitons, quenching by the electric field [99] or by polarons [100] is negligible under the conditions used in our experiments. For the triplet signal, either triplet transient absorption [90,101] or phosphorescence [85] could be used. However, both require large excitation densities to yield appropriate signal-to-noise ratios, which also causes migration activated TTA a major quenching channel [102,103].…”

Section: Experimental Observationsmentioning

confidence: 99%

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Singlet Generation from Triplet Excitons in Fluorescent Organic Light-Emitting Diodes

Monkman

2013

ISRN Materials Science

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A potential major drawback with organic light-emitting devices, (OLEDs) is the limit of 25% singlet exciton production through spin-dependent charge recombination. Recent device results, however, show that this limit does not hold and far higher efficiencies can be achieved in purely fluorescent-based systems (Wohlgenannt et al. (2012)). Here, the various routes by which triplet excitons can generate singlet states are discussed and their relative contributions to the overall electroluminescence yield are given. The materials requirements to obtain maximum singlet production from triplet states are discussed. These triplet contributions can give very high device yields for fluorescent emitters, which in the case of blue devices can be highly advantageous. Further, new devices architectures open up which are simple and have intrinsically low turn on voltages, ideal for large-area OLED lighting applications.

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Section: Isrn Materials Sciencecontrasting

confidence: 53%

Section: Exciton Formation In An Oledmentioning

confidence: 96%

Section: Experimental Observationsmentioning

confidence: 99%

Section: Experimental Observationsmentioning

confidence: 99%

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Singlet Generation from Triplet Excitons in Fluorescent Organic Light-Emitting Diodes

Monkman

2013

ISRN Materials Science

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“…This nonlinear loss mechanism for triplet excitons is in fact the reason why many previous studies drastically underestimated the number of triplet excitons generated, and thereby obtained excitation dependent (interpreted as electric fi eld-dependent) singlet exciton generation rates as high as 95%. 45,46 The results must therefore be studied and taken into account all together, in order to facilitate understanding.…”

Section: Annihilationmentioning

confidence: 99%

Chemical and photophysical properties of materials for OLEDs

Dechun

2013

Organic Light-Emitting Diodes (OLEDs)

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Spin Correlations in Organic Light‐Emitting Diodes

Walter

Lupton

2007

Highly Efficient OLEDs With Phosphorescent Materials

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A particular characteristic of organic materials used in light -emitting diodes is that they are predominantly composed of carbon and therefore only exhibit a very weak spin -orbit coupling. Electrically injected electrons and holes each carry spin 1/2 so that recombination can occur in a total of four spin combinations. It is an important question whether interconversion between the spin states can occur during electrostatic carrier capture prior to the formation of the ultimate excited state on the individual molecule, the singlet or the triplet exciton. Conjugated polymers containing minute quantities of spin -orbit enhancing heavy metal atoms open a unique window to spin dynamics in organic light -emitting diodes by enabling optically or electrically generated triplets to decay radiatively without impacting dramatically on the actual generation mechanism of triplets through excited state intersystem crossing. We show that optically generated singlet excitons can be electrically stabilized to prevent recombination. Storage of the charge carrier pair for tens of microseconds does not reveal a preference for delayed recombination in the lower energy triplet channel, suggesting that spin conversion in the charge carrier pair precursor state to exciton formation is rather ineffi cient. The message of this basic study of spin -lattice relaxation in excited states of organic fi lms to device engineers is that correlations between the spins of electrostatically bound carrier pairs are intrinsically remarkably stable. In the absence of a strong external mixing channel such as a heavy metal atom as in organometallic dopants it is expected that the dominant recombination in an organic lightemitting diode occurs in nonradiative triplets, forming a serious loss channel in actual devices. IntroductionThe most signifi cant difference between organic, carbon -based semiconductors and inorganic crystalline materials lies in the properties of the electron spin and the exchange interaction. Due to the low atomic order number of carbon, spin is 99 Highly Effi cient OLEDs with Phosphorescent Materials. Edited by H. Yersin

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Triplet-to-Singlet Exciton Formation in poly(p-phenylene-vinylene) Light-Emitting Diodes

Cited by 54 publications

References 15 publications

Singlet Generation from Triplet Excitons in Fluorescent Organic Light-Emitting Diodes

Singlet Generation from Triplet Excitons in Fluorescent Organic Light-Emitting Diodes

Chemical and photophysical properties of materials for OLEDs

Spin Correlations in Organic Light‐Emitting Diodes

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