Photocrosslinking of poly(N-vinylcarbazole): Implementing a complementary set of techniques to characterize the three-dimensional network formation

Bussière, Pierre‐Olivier; Mailhot, Bénédicte; Rivaton, Agnès; Barthe, M.F.; Gardette, Jean‐Luc; Baba, Mohamed

doi:10.1016/j.polymdegradstab.2008.03.025

Cited by 21 publications

(29 citation statements)

References 20 publications

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“…A three‐dimensional network is then progressively formed, which results in an increase of the stiffness. A similar scheme has already been proposed to explain the crosslinking of PVK under UV irradiation 21–23. The stiffness decrease observed after ∼60 h irradiation, can be attributed to the formation of oxidized sulfur‐containing moieties As sulfinate esters are end‐groups, their formation involves ring opening and chain scissions.…”

Section: Resultssupporting

confidence: 59%

“…These results suggest that, after a first 2N bond scission due to the direct light absorption of carbazole unit,21–23 the photo‐oxidation continues with the abstraction of a hydrogen atom from the tertiary C atom adjacent to the N atom (CH ter ) groups. The chain oxidation mechanism of the pendant side‐chain is likely to involve hydroperoxides which homolysis gives peroxy radicals evolving by β‐scission to give oxidation products 18.…”

Section: Resultsmentioning

confidence: 94%

“…Thiophene and benzothiadazole units were reported to be photochemically stable 16. However, recent studies concerning poly( N ‐vinylcarbazole) (PVK) indicated that the pendant carbazole units are photochemically unstable 21–23. Light absorption (λ > 300 nm) causes the homolysis of 2N bonds on the macromolecular chains, forming a carbazolyl radical and a macroradical on the polymeric chain.…”

Section: Introductionmentioning

confidence: 99%

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Impact of UV‐Visible Light on the Morphological and Photochemical Behavior of a Low‐Bandgap Poly(2,7‐Carbazole) Derivative for Use in High‐Performance Solar Cells

Tournebize

Bussière

Wong-Wah-Chung

et al. 2012

Advanced Energy Materials

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This paper reports on the photochemical behavior upon exposure to UV-visible light of a poly(2,7-carbazole) derivative for use in high-performance solar cells. Poly[ N -9 ′ -hepta-decanyl-2,7-carbazole-alt -5,5-(4 ′ ,7 ′ -di-2-thienyl-2 ′ ,1 ′ ,3 ′benzothiadiazole)] (PCDTBT) is one of a relatively large class of push-pull carbazole-based copolymers that have been synthesized to better harvest the solar spectrum. The 2,7-carbazole building block of PCDTBT is also used with different electron-accepting units in a large variety of low-band-gap polymers. The photochemical and morphological behavior of PCDTBT thin fi lms is investigated from the molecular scale to the nanomechanical properties. The photo-oxidation mechanism is shown to be governed by chain-scission and cross-linking reactions. It results in dramatic evolution of the morphology, roughness and stiffness of thin PCDTBT fi lms. Based on the identifi cation of several photoproducts formed along the macromolecular chains or released into the gas phase, the main pathways of PCDTBT photochemical evolution are discussed. These processes fi rst involve the scission of the C-N bond between the carbazole group and the tertiary carbon atom bearing the alkyl side-chain. Modifi cations of the chemical structure of PCDTBT, the evolution of its UV-visible absorbance, and its nanomechanical properties initiated by light irradiation are shown to be closely related. 479

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Section: Resultssupporting

confidence: 59%

Section: Resultsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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Impact of UV‐Visible Light on the Morphological and Photochemical Behavior of a Low‐Bandgap Poly(2,7‐Carbazole) Derivative for Use in High‐Performance Solar Cells

Tournebize

Bussière

Wong-Wah-Chung

et al. 2012

Advanced Energy Materials

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“…Few mechanisms like cleavage of the C-N bond in polycarbazole [ 45,46 ] and subsequent chain scission or crosslinking have been studied in detail. Few mechanisms like cleavage of the C-N bond in polycarbazole [ 45,46 ] and subsequent chain scission or crosslinking have been studied in detail.…”

Section: Describing Aging-induced V Oc Losses In Pcdtbt By Increased mentioning

confidence: 99%

Disorder‐Induced Open‐Circuit Voltage Losses in Organic Solar Cells During Photoinduced Burn‐In

Heumueller

Burke

Mateker

et al. 2015

Advanced Energy Materials

156

152

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different effect on device performance depending on the morphology of the active layer. We investigate this infl uence of morphology in the context of two fundamental mechanisms that are able to cause a V oc loss. First, an increased trap-assisted recombination rate that lowers the charge carrier density [ 2,3 ] and second a broadening of the density of states that reduces V oc [ 4,5 ] with the same charge carrier density and unchanged recombination dynamics. Answering this question is important not only for making more stable solar cells, but also for understanding in general how traps reduce the open-circuit voltage in organic solar cells. Aging is a convenient way to add traps into an organic solar cell and see their effect on recombination and V oc without introducing additional materials into the active layer.We illuminate BHJ solar cells of various materials in inert conditions for three days. Using transient photovoltage (TPV), [ 6 ] charge extraction (CE) [ 7 ] and temperature dependent measurements of the opencircuit voltage, we compare the recombination dynamics and charge carrier densities of fresh and aged solar cells and relate them to the observed V oc losses. We find that in degraded solar cells of amorphous materials such as poly[9′hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′benzothiadiazole)] (PCDTBT), the recombination dynamics are basically unchanged. Instead, the observed open-circuit voltage losses appear to result from increased energetic disorder that causes a change in the relevant low-energy portion of the density of states such that for the same charge carrier density a lower quasi Fermi level splitting is obtained. We observe that solar cells made from crystalline materials do not show V oc losses and have a higher charge carrier density than solar cells made from amorphous materials. Apparently crystalline materials are not affected by a moderate increase of energetic disorder, most likely due to a higher charge carrier density.Besides reduced open-circuit voltages, also losses of fi ll factor [ 1,8 ] and short-circuit current [ 9,10 ] are observed upon burnin. Often a convolution of degradation mechanisms at material interfaces and within the bulk of the absorbing layer is present. Recent work suggests that a decrease in fi ll factor during degradation is related to interface defects [ 1,8 ] which are most likely related to injection or extraction barriers at the electrodes. [11][12][13] The photoinduced open-circuit voltage ( V oc ) loss commonly observed in bulk heterojunction organic solar cells made from amorphous polymers is investigated. It is observed that the total charge carrier density and, importantly, the recombination dynamics are unchanged by photoinduced burn-in. Charge extraction is used to monitor changes in the density of states (DOS) during degradation of the solar cells, and a broadening over time is observed. It is proposed that the V oc losses observed during burn-in are caused by a redistribution of charge carriers in a broader DOS. The tempe...

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“…Porous materials such as alumina and silica were the first samples investigated using this technique [33,34]. The use of these materials, has permitted to extrapolate the behavior of different solvents to the study of polymeric and elastomeric systems [31,32,35] since polymeric swollen gels can be compared with the porous volume of inorganic materials. Consequently, it is then expected than thermoporosimetry provides information about distribution of pore sizes confining solvent in swollen crosslinked systems.…”

Section: Network Structure (Thermoporosimetry)mentioning

confidence: 99%

Structural evolution of a constrained epoxy functional polyethylene network crosslinked by a bio-based reactant

Garcia

Keromnes

Goutille

et al. 2014

European Polymer Journal

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Photocrosslinking of poly(N-vinylcarbazole): Implementing a complementary set of techniques to characterize the three-dimensional network formation

Cited by 21 publications

References 20 publications

Impact of UV‐Visible Light on the Morphological and Photochemical Behavior of a Low‐Bandgap Poly(2,7‐Carbazole) Derivative for Use in High‐Performance Solar Cells

Impact of UV‐Visible Light on the Morphological and Photochemical Behavior of a Low‐Bandgap Poly(2,7‐Carbazole) Derivative for Use in High‐Performance Solar Cells

Disorder‐Induced Open‐Circuit Voltage Losses in Organic Solar Cells During Photoinduced Burn‐In

Structural evolution of a constrained epoxy functional polyethylene network crosslinked by a bio-based reactant

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