Efficient red- and orange-light-emitting diodes realized by excitation energy transfer from blue-light-emitting conjugated polymers

Tasch, S.; List, Emil; Hochfilzer, C.; Leising, G.; Schlichting, P.; Rohr, U.; Geerts, Yves; Scherf, Ullrich; Müllen, Kläus

doi:10.1103/physrevb.56.4479

Cited by 135 publications

(62 citation statements)

References 32 publications

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“…(2), as shown in Fig. 3: We obtained W 5.5 6 0.5 eV, which is in excellent agreement with electron affinity measurements in mLPPP [21] [7] and may serve as an upper limit for l. From n 0 and the maximum thermalization rate, R th DE͞Dt, taken to be hn 2 [22], where hn ഠ 180 meV is the most strongly coupled vibration quantum (C--C stretching mode), we get a reasonable value for the attempt frequency to tunnel, n T R th n 0 ഠ 0.1n. We note that at high electric fields, F, of order 10 5 V͞cm, however, polaron photogeneration in a single chain becomes possible and a similar exciton dissociation model may also explain the F dependence of h͑E͒ observed in PC measurements [23].…”

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confidence: 75%

“…A combination of various incandescent lamps, diffraction gratings, optical filters, and solid state detectors was used to span the probe energy (hv) between 0.1 and 3 eV. The PM spectrum as a function ofhv was obtained by dividing the pump beam induced changes in transmission, DT ͑v͒, by the probe transmission T ͑v͒, where Da 2d 21 DT ͞T and d is the film thickness; DT was measured by a phase sensitive technique at f.…”

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confidence: 99%

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Photogeneration Action Spectroscopy of Neutral and Charged Excitations in Films of a Ladder-Type Poly(Para-Phenylene)

et al. 1999

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The photogeneration quantum efficiency action spectra of long-lived neutral and charged excitations in films of a ladder-type poly(para-phenylene) were measured. We found that both triplet and polaron action spectra show, in addition to a step function increase at the optical gap, a monotonic rise at higher energies. For triplets this rise is explained by singlet exciton fission into triplet pairs from which the triplet exciton energy in the gap was obtained; this energy was also confirmed by measuring the weak phosphorescence band. For polarons the photogeneration increase at high energies is modeled by a novel hot electron interchain tunneling process. [S0031-9007(99)08980-2] PACS numbers: 78.55. Kz, 72.20.Jv, 78.30.Jw, 78.66.Qn The photogeneration dynamics of singlet excitons and secondary photoexcitations, such as triplets and polarons, in p-conjugated polymers have been usually measured by picosecond transient spectroscopic techniques rather than cw spectroscopies, since their photogeneration processes usually occur in the subnanosecond time domain [1]. On the other hand, the excited states energy levels of these polymers are often measured by cw optical techniques including electroabsorption [2], resonant Raman scattering [3], and by two and three photon nonlinear optical spectroscopies [4]. In this Letter we employ a new version of the cw photomodulation (PM) spectroscopy technique, which is capable of measuring the photogeneration quantum efficiency, h, of long-lived secondary photoexcitations without the need of transient optical techniques. We show that when the PM signal is measured under conditions far from the steady state, then it directly correlates with h; therefore the PM action spectrum (PMAS) measured under these conditions gives the dependence of h on the excitation photon energy, E, i.e., h͑E͒.We have used the PMAS technique to obtain h͑E͒ of singlet and triplet excitons and polarons, respectively, in films of methyl-substituted ladder-type poly(paraphenylene) (mLPPP) [5] shown in Fig. 1, inset. mLPPP is an attractive p-conjugated polymer for blue-light emitting devices [6] due to its high photoluminescence (PL) quantum yield; this is caused, in part, by the intrachain order in the film induced by the planarization of neighboring phenyl rings [7]. mLPPP was chosen as a model polymer because of its reduced inhomogeneity and small defect density [8].For the excitation beam in the PMAS measurements we used either an Ar 1 laser at several discrete E, or a monochromatized xenon lamp beam to continuously vary E between 2 and 4.5 eV. The excitation beam was modulated with a chopper at a frequency, f, between 10 to 4 kHz. A combination of various incandescent lamps, diffraction gratings, optical filters, and solid state detectors was used to span the probe energy (hv) between 0.1 and 3 eV. The PM spectrum as a function ofhv was obtained by dividing the pump beam induced changes in transmission, DT ͑v͒, by the probe transmission T ͑v͒, where Da 2d 21 DT ͞T and d is the film thickness; DT was measu...

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confidence: 99%

Photogeneration Action Spectroscopy of Neutral and Charged Excitations in Films of a Ladder-Type Poly(Para-Phenylene)

et al. 1999

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“…1 Whereas initially significant effort was dedicated to development of blueemitting materials, 2-5 the focus has recently shifted to low-energy-gap materials for applications as long-wavelength absorbers in solar cells, 6 charge transporters in field-effect transistors, 7,8 as well as red 9,10 and near-infrared [11][12][13][14][15][16] emitters in organic light-emitting diodes (OLEDs). Many approaches have been proposed to obtain red and infrared emission from organic and solutionprocessable LEDs, including semiconductor nanoparticles, [17][18][19] conjugated small molecules, [11][12][13][14]20 conjugated polymers, 9,10,[21][22][23] and electrophosphorescence from transition metal 15 and rare earth complexes.…”

confidence: 99%

“…Many approaches have been proposed to obtain red and infrared emission from organic and solutionprocessable LEDs, including semiconductor nanoparticles, [17][18][19] conjugated small molecules, [11][12][13][14]20 conjugated polymers, 9,10,[21][22][23] and electrophosphorescence from transition metal 15 and rare earth complexes. 16,24 Of these, rare earth complexes offer some of the highest external quantum efficiencies, 25 with some reports in excess of 20%.…”

confidence: 99%

Efficient red electroluminescence from diketopyrrolopyrrole copolymerised with a polyfluorene

et al. 2013

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We report the synthesis, characterization, and device incorporation of copolymers based on a common green-emitting polyfluorene but containing a small proportion of a low energy gap donor-acceptor-donor unit for red emission in photo- and electro-luminescence. At just 1%–3% random incorporation, the low-gap unit is not present on all chains, yet we demonstrate that efficient charge and energy transfer can yield electroluminescent devices with 1% quantum efficiency and a color that can be tuned by adjusting the density of low-gap units to achieve primary red (National Television System Committee). The high current density tail off in the efficiency is reduced by replacing the hole-injection layer with a photochemically cross-linked electron‑blocking layer.

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“…5 A wide spectral range of emission colors, including white light, 6 can be accomplished using a polymerdoped active m-LPPP layer. 7 In addition, due to its wellresolved spectroscopic features in absorption and emission this material has been studied extensively as a model system with various cw ͑Ref. 8͒ and time resolved spectroscopic techniques.…”

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Localized triplet excitations and the effect of photo-oxidation in ladder-type poly(p-phenylene) and oligo(p-phenylene)

et al. 2000

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The photophysics of methyl-bridged poly͑para-phenylene͒-type ladder polymer ͑m-LPPP͒ and oligomer films and solutions is described and discussed. The spin sensitive properties, such as the formation and properties of polaron pairs and triplet excitons ͑TE's͒ were studied using X-band photoluminescence ͑PL͒ detected magnetic resonance ͑PLDMR͒. The PLDMR results and quantum chemical calculations show unambiguously that the TE wave-function extent is much smaller than that of the singlet exciton ͑SE͒. The weaker vibronic structure of the triplet photoinduced absorption ͑PA͒ band of m-LPPP relative to the singlet absorption is assigned to the small energy difference between the geometry of the lowest lying and excited triplet states. This is an additional indication of the strong localization of the triplet wave-function as compared to that of the SE. Finally, the influence of photo-oxidation on the PLDMR and PA is analyzed and discussed in relation to the photoconductivity of the materials.

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Efficient red- and orange-light-emitting diodes realized by excitation energy transfer from blue-light-emitting conjugated polymers

Cited by 135 publications

References 32 publications

Photogeneration Action Spectroscopy of Neutral and Charged Excitations in Films of a Ladder-Type Poly(Para-Phenylene)

Photogeneration Action Spectroscopy of Neutral and Charged Excitations in Films of a Ladder-Type Poly(Para-Phenylene)

Efficient red electroluminescence from diketopyrrolopyrrole copolymerised with a polyfluorene

Localized triplet excitations and the effect of photo-oxidation in ladder-type poly(p-phenylene) and oligo(p-phenylene)

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