Luminescence probing of crystallization in a polymer film

Granlund, Thomas; Pettersson, Lars; Andersson, Mats R.; Inganäs, Olle

doi:10.1063/1.373577

Cited by 7 publications

(9 citation statements)

References 38 publications

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“…39 In the following discussion, we rely on the sensitivity of photoluminescence spectra with respect to changes in order and morphology. 5,14,23 By using a series of four Gaussian functions, we simulated the vibronic progressions of the 0−0,…”

Section: Macromoleculesmentioning

confidence: 99%

“…In order to understand optoelectronic properties of conjugated polymer systems and to establish ways for enhancing their performance in optoelectronic applications, previous studies have measured absorption and emission spectra as a function of packing and order in thin films. − To a large extent, optical properties of conjugated systems are determined by intra- and interchain interactions, , which also strongly influence energy and charge transfer. A conjugated polymer chain can be viewed as a system of many coupled chromophores.…”

Section: Introductionmentioning

confidence: 99%

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Signatures of Melting and Recrystallization of a Bulky Substituted Poly(thiophene) Identified by Optical Spectroscopy

Keheze

Raithel

et al. 2017

Macromolecules

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As-cast and slowly crystallized films of conjugated polymers can contain (partially) ordered and less ordered (amorphous) regions with structural defects. Crystallization allows to generate chains with highly planarized backbones, embedded in structures exhibiting long-range order. In the present study, we used spatially resolved optical spectroscopy to quantify differences in the degree of order of a bulky substituted poly(3-(2,5-dioctylphenyl)thiophene) (PDOPT). In particular, we compared absorption and photoluminescence (PL) measurements from large spherulitic crystals, and the same region rapidly recrystallized after melting, which allowed to identify characteristic features of ordered and less ordered regions. In addition, on the basis of temperature-dependent absorbance and PL measurements, we followed in situ melting and recrystallization processes, i.e., transitions between ordered and disordered phases. A multipeak analysis of absorption and PL spectra based on a modified Franck−Condon progression showed changes in for example the relative intensities of each peak, the excitonic bandwidth, and the vibronic energy as a function of temperature. Most importantly, at the phase transition temperature, a clear change in the positions of the peaks (i.e., their wavelengths, corresponding to the energy of the emitted photons) was detected. In particular, the relative absorption and PL intensities depended sensitively on the extent of order within PDOPT samples. Furthermore, on the basis of a comparison with calorimetric measurements, we have confirmed correlations between changes in the relative absorbance and PL intensities with variations in order/disorder occurring during melting and recrystallization.

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Section: Macromoleculesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Signatures of Melting and Recrystallization of a Bulky Substituted Poly(thiophene) Identified by Optical Spectroscopy

Keheze

Raithel

et al. 2017

Macromolecules

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“…[121,122] The same microcavity optics was shown to be valid for photoluminescence in a halfcavity [123] or into a symmetric cavity, [124] one of the early optically pumped polymer lasers. Therefore, coherence of light can be the standard condition, and interference becomes an important element adding an optical mode structure into devices.…”

Section: Optical Mode Structure In Thin Film Devicesmentioning

confidence: 92%

“…The theory of microcavity optics was already demonstrated in the thin film OLEDs, and we did model the spectral changes due to light emission into a halfcavity, with one strong reflector. [121,122] The same microcavity optics was shown to be valid for photoluminescence in a halfcavity [123] or into a symmetric cavity, [124] one of the early optically pumped polymer lasers. Optical mode structure of bilayer diode with a polythiophene combined with a thin or thick C60 layer, illuminated with 460 nm monochromatic light.…”

Section: Optical Mode Structure In Thin Film Devicesmentioning

confidence: 99%

Organic Photovoltaics over Three Decades

2018

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The development of organic semiconductors for photovoltaic devices, over the last three decades, has led to unexpected performance for an alternative choice of materials to convert sunlight to electricity. New materials and developed concepts have improved the photovoltage in organic photovoltaic devices, where records are now found above 13% power conversion efficiency in sunlight. The author has stayed with the topic of organic materials for energy conversion and energy storage during these three decades, and makes use of the Hall of Fame now built by Advanced Materials, to present his view of the path travelled over this time, including motivations, personalities, and ambitions.

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“…The luminescence maximum at 1.7 eV has a shoulder at 1.85 eV, in good agreement with the literature. 16,17 The absorption and photoluminescence spectra of P3OT on quartz and on TiO 2 are similar, which allows us to use the intensity of the 1.7 eV maximum as a measure for the total intensity of the photoluminescence. For irradiated P3OT films deposited on TiO 2 , the generated excitons that reach the active P3OT/TiO 2 interface are quenched and a reduction of the photoluminescence is expected.…”

mentioning

confidence: 99%

Enhanced photoluminescence at poly(3-octyl-thiophene)/TiO2 interfaces

Zanden

Krol

Schoonman

et al. 2004

Applied Physics Letters

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The photoluminescence ͑PL͒ of poly͑3-octyl-thiophene͒ ͑P3OT͒ thin films applied on TiO 2 substrates is compared to the PL of P3OT films applied on quartz. Quenching of excitons occurs at the P3OT/TiO 2 interface and not at the P3OT/quartz interface. Yet, in the former case the PL intensity is stronger than in the latter. In particular, P3OT films less than 5 nm thick lumines much more when applied on TiO 2 , which is in striking contrast to what one expects. For films thicker than 10 nm, the increase of the PL as function of the film thickness is the same for TiO 2 and for quartz, which indicates that the PL enhancement originates at the interface. The dissociation of excitons at the P3OT/TiO 2 interface yields positive polarons in P3OT, which is not the case at the P3OT/quartz interface. We postulate that interaction between positive polarons and excitons explain the observed enhancement of the PL at the P3OT/TiO 2 interface. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1699447͔The study of photoluminescence ͑PL͒ spectra of conjugated polymers, applied on metal-oxide substrates, is a powerful tool to investigate energy and charge-transfer mechanisms at active and nonactive interfaces. These interfaces are important in polymer solar cells and in polymer lightemitting diodes ͑poly-LEDs͒. In the field of polymer solar cells, charge transfer from the polymer to an electron acceptor, such as a fullerene, CdSe, or TiO 2 , is generally accompanied by quenching of the photoluminescence. 1-3 For polyLEDs the ratio between the electroluminescence and photoluminescence quantum yields is limited to 25% by spin-degeneracy statistics. 4 However, recent studies by Beljonne et al., 5 Ye et al., 6 and references therein, reveal that the singlet/triplet formation ratio can be broken by interchain mechanisms. In that case the 25% rule no longer applies. The observations presented in this letter are in line with these theoretical considerations. While charge carrier generation and transport in polythiophene films have been investigated thoroughly, 7-14 the interaction between positive polarons and excitons has not been taken into account. In the present letter we report on the enhancement of the poly͑3-octyl-thiophene͒ ͑P3OT͒ photoluminescence when applied onto TiO 2 versus when applied onto quartz. In the first case, positive, polarons are generated in P3OT and in the latter case not. Our experimental results strongly suggest that positive polarons can interact with nonemissive excitons to give them more radiative character. Future experiments and theoretical studies are required to elucidate exciton-polaron interactions in more detail.An 80 nm flat film of anatase TiO 2 was deposited on quartz and on SnO 2 :F-coated glass by chemical vapor deposition, using Titanium-Tetra-Iso-Propoxide as precursor ͑Everest Coatings, The Netherlands͒. Prior to application of the polymer film, the TiO 2 film was dried in air for 1 h at 250°C. For some experiments the TiO 2 surface was chemically modified, by soaking the TiO 2 films overn...

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Luminescence probing of crystallization in a polymer film

Cited by 7 publications

References 38 publications

Signatures of Melting and Recrystallization of a Bulky Substituted Poly(thiophene) Identified by Optical Spectroscopy

Signatures of Melting and Recrystallization of a Bulky Substituted Poly(thiophene) Identified by Optical Spectroscopy

Organic Photovoltaics over Three Decades

Enhanced photoluminescence at poly(3-octyl-thiophene)/TiO2 interfaces

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