Phase behavior of blends of PCBM with amorphous polymers with different aromaticity

Bernardo, Gabriel; Deb, Nabankur; King, Stephen M.; Bucknall, David G.

doi:10.1002/polb.24002

Cited by 18 publications

(17 citation statements)

References 27 publications

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“…The calculation of the error bars in b and e is described in the text. All data in this figure is for ex-situ annealed samples on the order of a few nm to tens of nm 23 , with a recently reported value for a (miscible) blend of around 10%-PCBM in PS (by volume) equal to 60 ± 40 nm 61 . However, the in-plane distances to which off-specular neutron scattering is sensitive are on the order of a few hundred nm to a few microns 51 .…”

Section: Resultsmentioning

confidence: 63%

“…Dispersion forces are expected to predominate in these systems 62 , giving increased mixing for increased chemical similarity between species. This is evidenced experimentally by the report of increased mixing in polymer/fullerene systems (using polymers with non-conjugated backbones mixed with either C 60 or PCBM) as side-groups with increasing aromatic character are incorporated within the polymer 61 . Also, an increase in chemical similarity in conjugated-polymer/fullerene systems (on moving from bis-PCBM to PCBM) is reported to drive increased mixing 20 .…”

Section: Resultsmentioning

confidence: 96%

“…4a). The additional side-chain simplifies the system by inhibiting crystallisation of this fullerene 60 and also affects miscibility with solvents and polymers 20,61,62 . In this system, both bilayer models (with Gaussian interface roughness at the buried interface and surface) and multilayer models (using multiple layers, but with Gaussian roughness at the sample surface only and zero roughness at all internal interfaces) were fitted to the reflectivity data.…”

Section: Resultsmentioning

confidence: 99%

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Interfacial width and phase equilibrium in polymer-fullerene thin-films

et al. 2019

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Domain composition and interfacial structure are critical factors in organic photovoltaic performance. Here, we report neutron reflectivity, grazing-incidence X-ray diffraction and atomic force microscopy measurements of polymer/fullerene thin-films to test a hypothesis that these partially miscible blends rapidly develop composition profiles consisting of coexisting phases in liquid-liquid equilibrium. We study a range of polymer molecular weights between 2 and 300 kg mol −1 , annealing temperatures between 120 and 170 o C, and timescales up to 10 min, yielding over 50 distinct measurement conditions. Model bilayers of fullerene-derivatives and polystyrene enable a rigorous examination of theoretical predictions of the effect of polymer mass and interaction parameter on the compositions, ϕ, and interfacial width, w, of the coexistent phases. We independently measure ϕ and w and find that both Flory-Huggins mean-field-theory and key aspects of self-consistent-field-theory are remarkably consistent with experiment. Our findings pave the way for predictive composition and interface design in organic photovoltaics based on simple experimental measurements and equilibrium thermodynamic theory.

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Section: Resultsmentioning

confidence: 63%

Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

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Interfacial width and phase equilibrium in polymer-fullerene thin-films

et al. 2019

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“…This result is not unexpected as 85 °C is below the glass transition temperature of the polymer matrix ( T g (PS) ≈ 100 °C), which is not expected to be significantly affected by addition of fullerenes . While photoexcitations with energy greater than the bandgap can relax to the band edge, potentially releasing excess energy as a phonon, and in turn cause local temperature hot spots, such photo‐induced local heating effects, if present, are modest and do not result in morphological instability, even in the vicinity of T g (PS).…”

Section: Resultsmentioning

confidence: 76%

Stability of Polymer:PCBM Thin Films under Competitive Illumination and Thermal Stress

Pont

Foglia

Higgins

et al. 2018

Adv Funct Materials

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The combined effects of illumination and thermal annealing on the morphological stability and photodimerization in polymer/fullerene thin films are examined. While illumination is known to cause fullerene dimerization and thermal stress their dedimerization, the operation of solar cells involves exposure to both. The competitive outcome of these factors with blends of phenyl-C61-butyric acid methyl ester (PCBM) and polystyrene (PS), supported on PEDOT:PSS is quantified. UV-vis spectroscopy is employed to quantify dimerization, time-resolved neutron reflectivity to resolve the vertical composition stratification, and atomic force microscopy for demixing and coarsening in thin films. At the conventional thermal stress test temperature of 85 °C (and even up to the PS glass transition), photodimerization dominates, resulting in relative morphological stability. Prior illumination is found to result in improved stability upon high temperature annealing, compatible with the need for dedimerization to occur prior to structural relaxation. Modeling of the PCBM surface segregation data suggests that only PCBM monomers are able to diffuse and that illumination provides an effective means to control dimer population, and thus immobile fullerene fraction, in the timescales probed. The results provide a framework for understanding of the stability of organic solar cells under operating conditions.

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“…Additionally, the structural and energetic disorder that results from the presence of different At this point, we note that fullerene functionalization can affect the efficiency of OPVs in different ways. Besides changing the HOMO/LUMO levels, different functional groups appended to the fulleropyrrolidines also affect the polymer-fullerene interactions and consequently the degree of fullerene dispersion in the polymer [64][65][66]. As a result, fullerenes with similar µ e values in their pure state may originate BHJs with very different µ e values due to different nanoscale morphologies [67,68].…”

Section: Resultsmentioning

confidence: 99%

PffBT4T-2OD Based Solar Cells with Aryl-Substituted N-Methyl-Fulleropyrrolidine Acceptors

et al. 2019

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Novel C60 and C70 N-methyl-fulleropyrrolidine derivatives, containing both electron withdrawing and electron donating substituent groups, were synthesized by the well-known Prato reaction. The corresponding highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy levels were determined by cyclic voltammetry, from the onset oxidation and reduction potentials, respectively. Some of the novel fullerenes have higher LUMO levels than the standards PC61BM and PC71BM. When tested in PffBT4T-2OD based polymer solar cells, with the standard architecture ITO/PEDOT:PSS/Active-Layer/Ca/Al, these fullerenes do not bring about any efficiency improvements compared to the standard PC71BM system, however they show how the electronic nature of the different substituents strongly affects the efficiency of the corresponding organic photovoltaic (OPV) devices. The functionalization of C70 yields a mixture of regioisomers and density functional theory (DFT) calculations show that these have systematically different electronic properties. This electronic inhomogeneity is likely responsible for the lower performance observed in devices containing C70 derivatives. These results help to understand how new fullerene acceptors can affect the performance of OPV devices.

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Phase behavior of blends of PCBM with amorphous polymers with different aromaticity

Cited by 18 publications

References 27 publications

Interfacial width and phase equilibrium in polymer-fullerene thin-films

Interfacial width and phase equilibrium in polymer-fullerene thin-films

Stability of Polymer:PCBM Thin Films under Competitive Illumination and Thermal Stress

PffBT4T-2OD Based Solar Cells with Aryl-Substituted N-Methyl-Fulleropyrrolidine Acceptors

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